Showing posts with label Abrupt Climate Change -- ACC. Show all posts

Written by fatih al-farahat in , ,


Anders Levermann: Global warming increases the risk of abrupt monsoon transitions from high-precipitation to dry periods

Monsoon model indicates potential for abrupt transitions

ScienceDaily, October 16, 2009 — A self-amplifying effect presently sustains monsoon winds, but it could also disrupt the circulation over land and sea. The periodical rainfall could stop from one season to another or for months within seasons. High air pollution could lead to the disruption, researchers of the Potsdam Institute for Climate Impact Research report in the Proceedings of the National Academy of Sciences, Online Early Edition. Global warming increases the risk of abrupt monsoon transitions from high-precipitation to dry periods.

"The agricultural food supply for around two billion people in Asia and Africa depends on the eponymous regularity of monsoon rainfall," says the lead author Anders Levermann. The name "monsoon" stems from the Arabic word "mausim" for "season." However, months with extremely scarce precipitation have been observed within monsoon seasons, as in India in 2002, causing economic and humanitarian problems in the affected regions. During the past 11,000 years rainfall in monsoon regions has undergone strong and abrupt changes repeatedly.

The researchers investigated how such irregularities or disruptions of monsoon circulations can come about. "Our analysis shows on the basis of observations that there could be two stable states for monsoon systems and the possibility of abrupt transitions from one to the other," says Levermann.

The driving force of monsoon systems depends on different air temperatures. In spring, the air over land is warmed up more rapidly than the air over the sea. The warmer air rises and moist and cooler air from the ocean flows landwards and yields precipitation, which has two effects: the rainfall cools the land surface, but also releases latent heat, when water vapour condenses to raindrops. The more moist air is transported landwards, the more latent heat is released through rainfall and the more moist air is drawn towards land. This self amplification, named moisture-advection feedback, sustains the temperature difference and the entire circulation. However, the self-amplification is vulnerable and may lead to abrupt changes in response to relatively weak external perturbations, the authors state.

The PIK researchers now present a conceptual model that captures the self-amplification feedback. The basic equations show that there is a critical value of irradiation from the sun for a monsoon circulation to start. If irradiation falls below the critical value, for instance due to high air pollution, no conventional monsoon can develop. Above the critical value, one state with and one state without a monsoon circulation exist.

This allows for an abrupt transition to occur in one of two different ways. First, climatic shifts can push the system across the critical threshold. The transition would occur from one season to the other and last as long as the climatic shift prevails. The second possibility is abrupt transitions between the two stable states, when the system is -- as current monsoon circulations are -- in the bi-stable regime above the critical threshold. Within one rainy season weakening of monsoon winds and latent heat release could decrease the temperature difference between land and sea until the circulation is disrupted.

Using the model and observational data from the past 60 years the researchers computed the critical values for monsoon systems in India, China, Bangladesh, West Africa, North America and Australia. "We are working on more precise assessments of the vulnerabilities of monsoon systems," says co-author Jacob Schewe. Currently, large uncertainties still exist. While global warming would increase precipitation, aerosol emissions, especially in countries like India and China, could reduce monsoon stability. "Oscillations between months with strong and months with extremely weak rainfall could overstrain the people's capacity to adapt," says Schewe. Thus, the researchers want to further investigate the risks for abrupt monsoon transitions in the respective regions. The article "Basic mechanism for abrupt monsoon transitions" will appear in print in a Special Feature of the Proceedings of the National Academy of Sciences. The Special Feature contains analyses of eight potential tipping elements in the Earth System and is edited by Hans Joachim Schellnhuber, director of PIK.

Adapted from materials provided by Potsdam Institute for Climate Impact Research (PIK).

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J. P. Steffensen et al., Science 2008, High-resolution Greenland ice core data show abrupt climate change happens in few years

Science, published online June 19, 2008

High-resolution Greenland ice core data show abrupt climate change happens in few years

J. P. Steffensen et al.


Abstract

The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, are investigated in high temporal resolution from the Greenland NGRIP ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switches mode within 1 to 3 years over these transitions and initiates a more gradual change (50 years) of the Greenland air temperature as recorded by water stable isotopes. The onsets of both abrupt Greenland warmings are slightly preceded by decreasing Greenland dust deposition, reflecting wetting of Asian deserts. A northern shift of the ITCZ could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in 2 to 4K changes in Greenland moisture source temperature from one year to the next.

Link to abstract:  http://www.sciencemag.org/cgi/content/abstract/1157707v1

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Cutting non-CO2 pollutants can delay abrupt climate change, solve “fast half” of climate problem



Cutting non-CO2 pollutants can delay abrupt climate change,
solve “fast half” of climate problem 
           
Washington, D.C., October 12, 2009 – Reducing non-CO2 climate change agents such as black carbon soot, tropospheric ozone, and hydrofluorocarbons (HFCs), as well as expanding bio-sequestration through biochar production, can forestall fast approaching abrupt climate changes, according to Nobel Laureate Dr. Mario Molina and co-authors in a paper published today in the Proceedings of the National Academy of Sciences (PNAS).

The paper’s authors said that pursuing these solutions could change the character of the United Nations climate change conference taking place this December in Copenhagen.

“Cutting HFCs, black carbon, tropospheric ozone, and methane can buy us about 40 years before we approach the dangerous threshold of 2 ˚C warming,” said co-author Professor Veerabhadran Ramanathan, a Distinguished Professor of Climate and Atmospheric Sciences at Scripps Institution of Oceanography at the University of California, San Diego.

“By targeting these short-term climate forcers, we can make a down payment on climate and provide momentum going into the December negotiations in Copenhagen,” said co-author Durwood Zaelke, President of the Institute for Governance & Sustainable Development.  “The Obama Administration and other key governments need to take up the fast-action climate agenda before it is too late.”

HFCs are powerful greenhouse gases originally developed as substitutes for ozone-depleting chemicals.  They are poised to become a larger part of the climate problem over the next few decades. HFCs are used primarily as refrigerants and in making insulating foam, and emissions are expected to grow dramatically due to increased demand for air conditioning in developing countries.  By 2050, HFC emissions could equal up to 19% of global CO2 emissions under business-as-usual scenarios. The good news, the paper points out, is that a binding legal agreement exists that can cut HFCs now—the Montreal Protocol ozone treaty—and that many alternatives to HFCs have already been developed and are on the shelf waiting for the right regulatory incentive from the Montreal Protocol to be deployed.

 “The Montreal Protocol has already delayed climate change by seven to 12 years, and put the ozone layer on the path to recovery later this century,” said Dr. Mario Molina, recipient of the Nobel Prize in chemistry for his path-breaking work in 1974 that sounded the alarm on ozone-depleting CFCs. “The Montreal Protocol is critical for avoiding abrupt climate change.  We have to take advantage of the proven ability of this legally binding treaty to quickly phase down HFCs.”  

The small island nations of Micronesia and Mauritius submitted a joint proposal in April to phase down production and consumption of HFCs under the Montreal Protocol. North American leaders followed suit with their own joint proposal, which builds on the islands’ submission. The Montreal Protocol is an essential strategy for the island nations to achieve fast mitigation to slow sea-level rise that is already starting to destroy their countries. “We must consider all viable strategies that will help protect vulnerable island nations, in particular, those strategies that have a track record of success, such as the Montreal Protocol,” said Ambassador Masao Nakayama, Permanent Representative of the Federated States of Micronesia to the United Nations. Although the Kyoto Protocol currently addresses emissions of HFCs, it does not address production and consumption.

A neglected fast-action strategy presented in the paper is reducing black carbon soot, an aerosol produced largely from the incomplete combustion of diesel fuels and biofuels, and from biomass burning.  It is now considered to be the second or third largest contributor to climate change.  Black carbon is responsible for almost 50% of the 1.9˚C increase in warming of the Arctic since 1890, as well as significant melting of the Himalaya-Tibetan glaciers that feed the major rivers of Asia, providing fresh water to billions of people. 

Researchers consider black carbon an ideal target for achieving quick mitigation because it only remains in the atmosphere a few days to a few weeks and can be reduced by expanding the use of diesel particulate filters for vehicles and clean-burning or solar cookstoves to replace those burning dung and wood. With indoor air pollution killing 1.6 million people a year, global action to cut soot emissions would reap major benefits for both public health and climate.

 “If we reduce black carbon emissions worldwide by 50% by fully deploying all available emissions-control technologies, we could delay the warming effects of CO2 by one to two decades and at the same time greatly improve the health of those living in heavily polluted regions,” said Dr. Ramanathan.

Like black carbon, ground level or tropospheric ozone doubles as a major climate forcer and health hazard. It also lowers crop yields. A recent study reported that ozone’s damage to crop yields in 2000 resulted in an economic loss of up to $26 billion annually. It is formed by “ozone precursor” gases such as carbon monoxide, nitrogen oxides, methane, and other hydrocarbons, many of which can be reduced by improving the efficiency of industrial combustion processes. Reducing tropospheric ozone by 50% could buy another decade’s worth of time for countries to start making substantial cuts in CO2.

Biochar is one of the few promising “carbon-negative” strategies that can drawdown existing concentrations of CO2. The fine-grained charcoal product is a stable form of carbon that can be plowed into soil where it remains for hundreds to thousands of years, also serving as a natural fertilizer. Biochar comes from cooking biomass waste at low temperatures with minimal oxygen—a process called pyrolisis. “The other fast-action strategies can quickly mitigate emissions, but to back away from the cliff of abrupt climate change, we need biochar,” said Zaelke.

Although most of the world is focused on CO2 in the months leading up to Copenhagen, the authors of the paper hope that policymakers will recognize the advantages of implementing these fast-action strategies to complement reductions in CO2. “These fast-action strategies will support the long-term CO2 solution by stopping near-term climate change with non-CO2 solutions,” said Dr. Stephen Andersen. “This will bring momentum to those negotiating the international agreement and the U.S. legislation.”

The paper is part of a “Tipping elements in Earth systems” special feature to be published in PNAS later this year. 

“Cutting CO2 emissions is essential, but it won’t produce cooling fast enough to avoid passing tipping points for abrupt climate change,” said Zaelke. “With the world already committed to more than 2˚C of warming, we need these fast-action strategies to put the brakes on climate change, and in the case of biochar, put us in reverse by reducing existing atmospheric concentrations of CO2.”

“We intend our paper as a call to action,” said co-author K. Madhava Sarma of the Montreal Protocol’s Technology and Economic Assessment Panel.

###

Title: Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

Authors:  Mario Molina, Durwood Zaelke, K. Madhava Sarma, Stephen O. Andersen,
Veerabhadran Ramanathan and Donald Kaniaru

Available online: http://www.pnas.org/content/early/2009/10/09/0902568106.full.pdf+html
 

For further information on the Montreal Protocol and its contribution to climate protection:

IGSD background note on Montreal protocol: http://www.igsd.org/documents/OzoneDayPR15Sept1055am.pdf

IGSD press release on “North American leaders submit joint proposal to phase down HFCs under Montreal Protocol”: http://www.igsd.org/documents/PR_NAHFCproposal1245pm.pdf

Contact: Alex Viets, IGSD: +1.213.321.0911 or +1.202.498.2457, aviets@igsd.org

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M. Molina et al., PNAS, Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

Proceedings of the National Academy of Sciences, published online before print October 12, 2009; doi: 10.1073/pnas.0902568106

Reducing abrupt climate change risk using the Montreal Protocol and other regulatory actions to complement cuts in CO2 emissions

Mario Molina, Durwood Zaelke*, K. Madhava Sarma, Stephen O. Andersen, Veerabhadran Ramanathan and Donald Kaniaru

Edited by Hans Joachim Schellnhuber, Environmental Change Institute, Oxford, U.K., and approved August 31, 2009 (received for review March 9, 2009).

Abstract

Current emissions of anthropogenic greenhouse gases (GHGs) have already committed the planet to an increase in average surface temperature by the end of the century that may be above the critical threshold for tipping elements of the climate system into abrupt change with potentially irreversible and unmanageable consequences. This would mean that the climate system is close to entering if not already within the zone of “dangerous anthropogenic interference” (DAI). Scientific and policy literature refers to the need for “early,” “urgent,” “rapid,” and “fast-action” mitigation to help avoid DAI and abrupt climate changes. We define “fast-action” to include regulatory measures that can begin within 2–3 years, be substantially implemented in 5–10 years, and produce a climate response within decades. We discuss strategies for short-lived non-CO2 GHGs and particles, where existing agreements can be used to accomplish mitigation objectives. Policy makers can amend the Montreal Protocol to phase down the production and consumption of hydrofluorocarbons (HFCs) with high global warming potential. Other fast-action strategies can reduce emissions of black carbon particles and precursor gases that lead to ozone formation in the lower atmosphere, and increase biosequestration, including through biochar. These and other fast-action strategies may reduce the risk of abrupt climate change in the next few decades by complementing cuts in CO2 emissions. 

*Correspondence; e-mail: dzaelke@igsd.org or zaelke@inece.org

Link to abstract:  http://www.pnas.org/content/early/2009/10/09/0902568106.abstract

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Crossing planetary boundaries (irreversible tipping points, or points of no return as James Hansen calls them), Nature study by Rockstrom et al.

23 Sep 2009: Analysis

Provocative New Study Warns of Crossing Planetary Boundaries

The Earth has nine biophysical thresholds beyond which it cannot be pushed without disastrous consequences, the authors of a new paper in the journal Nature report. Ominously, these scientists say, we have already moved past three of these tipping points.

by Carl Zimmer, environment360, September 23, 2009

Human civilization has had a stable childhood. Over the past 10,000 years, as our ancestors invented agriculture and built cities, the Earth remained relatively stable. The average global temperature fluttered slightly, never lurching towards a greenhouse climate or chilling enough to enter a new Ice Age. The pH of the oceans remained steady, providing the right chemical conditions for coral reefs to grow and invertebrates to build shells. Those species, in turn, helped support a stable food web that provided plenty of fish for us humans to catch. The overall stability of the past 10,000 years may have played a big part in humanity’s explosion.

Now, ironically, civilization has become so powerful that it can reshape the planet itself. “We have become a force to contend with at the global level,” as Johan Rockstrom of the Stockholm Resilience Center in Sweden, puts it. Humans have changed the chemistry of Earth’s oceans, turning them acidic. We are shifting the composition of the atmosphere, raising levels of carbon dioxide higher than they’ve been in at least the past 800,000 years."

A number of scientists have warned in recent years that if we keep pushing the planet this way, we will cause sudden, irreversible damage to the systems that made human civilization possible in the first place. Typically, they’ve just focused on one of these tipping points at a time. But in today’s issue of the journal Nature, Rockstrom and 27 of his fellow environmental scientists argue that we have to conceive of many tipping points at once. They propose that humans must keep the planet in what they call a “safe operating space,” inside of which we can thrive. If we push past the boundaries of that space — by wiping out biodiversity, for example, or diverting too much of the world’s freshwater — we risk catastrophe.

Unfortunately, the authors of the Nature paper maintain, we’ve already started pushing out beyond these boundaries without knowing where they actually are. “We’re sitting on top of a mesa right now, and we’re driving

Nature
Nature
CLICK TO ENLARGE: Overstepping the world’s “planetary boundaries”
around, but we don’t have our lights on and we don’t even have a map,” says Jonathan Foley, a co-author of the new study and the director of the University of Minnesota’s Institute on the Environment. “That’s a dangerous way to move around.”

In their new study, Foley and his colleagues put down stakes to mark where they believe seven of these boundaries lie. By their estimate, we have already pushed beyond three of these boundaries, and are moving quickly toward the other four. “We’re running out of time,” says Rockstrom.

The new paper has already drawn strong reactions from other scientists, some glowing, some harsh. “This kind of work is critically important,” says Christopher Field, the director of the Department of Global Ecology at the Carnegie Institution at Stanford University. “Overall, this is an impressive attempt to define a safety zone.”

But other scientists wonder whether a planetary safety zone is a concept worth bothering with. “I don’t think this is in any way a useful way of thinking about things,” says Stuart Pimm, a conservation biologist at Duke University.

Rockstrom and his colleagues developed the concept of planetary boundaries from earlier work on how natural systems change. Those changes are sometimes gradual, but they can also come in jolts. A lake, for example, can absorb a fair amount of phosphorus from fertilizer runoff
In five areas, the scientists found, the world has not yet reached the danger threshold.
without any sign of change. “You add a little, not much happens,” says Shahid Naeem of Columbia University, who was not involved in the Nature paper. “Add a little more, not much happens. Add a little... then, all of sudden, you add a little more and — boom! — phytoplankton bloom, oxygen depletion, fish die-off, smelliness. Remove the little phosphorus that caused the tipping of the system, and it does not reverse. In fact, you have to go back to much cleaner water than you would have imagined.”

In recent years, some scientists have argued that the entire planet behaves in a similar way. Adding extra greenhouse gases can raise the planet’s temperature in a steady, proportional rate. But there may come a point when the climate will get pushed into a drastically new state. Some climate scientists have argued, for example, that global warming may trigger the runaway collapse of ice sheets in Greenland and Antarctica. Even if we then immediately stopped emitting greenhouse gases, the ice sheets would keep collapsing into the sea. And then we couldn’t do anything to reverse the change. “We don’t know how to refreeze the Greenland ice sheet,” says Rockstrom.

Rockstrom helped organize a workshop in Stockholm in April 2008 where environmental scientists talked about the other possible thresholds that might exist on a global scale. They concluded that there was good evidence for nine kinds of thresholds: climate change, ocean acidity, the ozone layer, freshwater use, the movement of nitrogen and phosphorus, the amount of land used for crops, aerosols (haze and other particles), biodiversity, and chemical pollution.

The scientists then reviewed each of those factors to mark boundaries that the world should not push beyond. “The idea is to say, ‘Let’s put up some guard rails,’” says Robert Costanza of the University of New Hampshire. “Maybe the guard rails are for a slope we could have taken and survived, but maybe not. We owe it to human civilization to be more careful.”

Ultimately, the scientists felt confident in estimating seven boundaries, three of which we have already pushed past. For one thing, they argue, we’ve already put too much carbon dioxide in the atmosphere. James Hansen, a NASA climate scientist and co-author of the Nature paper, has argued that to avoid catastrophic melting of ice sheets, we should keep carbon dioxide levels no higher than 350 parts per million. Before the Industrial Revolution, the concentration was at about 280 parts per million, but today we’re up to 387. In other words, we’ve moved out of the safe operating space — and into risky territory.

The scientists also argue that as we spread fertilizer on farmland and burn coal, we are pumping far too much nitrogen into the environment. Human activity releases 121 million tons of nitrogen, much of which ends up polluting rivers, lakes and oceans and potentially pushing their ecosystems into irreversible changes. At most, the scientists argue, less than 35 million tons of nitrogen would be a safe boundary.

The rate at which species are becoming extinct is also far beyond a safe boundary, according to the scientists. During most of the history of life, species have become extinct at a slow, fairly regular pace. And as old
The concept of boundaries is provocative because it highlights how much scientists don’t yet understand.
species have become extinct, new ones have been evolving. There have been times when many species have become extinct at a much faster rate, and these pulses have sometimes ushered in a global collapse of ecosystems. The authors of the new Nature paper propose that to avoid collapse, the extinction rate cannot rise above 10 times the long-term background rate. Today, however, scientists estimate that the extinction rate is 100 to 1,000 times higher.

In five other areas, the scientists found, we have not yet crossed the boundary into the danger zone. As we release carbon dioxide, for example, some of it goes into the oceans and makes it more acidic. In acidic seawater, coral reefs have a harder time building skeletons, because the minerals they produce for their skeletons quickly dissolve. Invertebrates have the same trouble making shells. According to recent surveys, the ocean is now acidifying 100 times faster than at any time during the past 20 million years. Yet the Nature co-authors estimate that we have not yet reached the point where acidity may cause ecological collapse. But we are close.

While the paper makes for a sobering read, its authors think we should also find some cause for optimism in it. Humanity nearly crossed another threshold by destroying the ozone layer with chlorofluorocarbons. But we recognized the crisis in time and banned chlorofluorocarbons, allowing the ozone layer to slowly recover. If we had waited much longer we might have been too late to do anything. “We were able to avoid a global disaster,” says Rockstrom. He hopes we can do the same again, and keep human civilization from falling off the environmental mesa.

“The authors make a strong case for their selection of key boundaries,” says the Carnegie Institution’s Christopher Field, “and the proposed locations for the boundaries are conceptually reasonable.” Field said he would not be surprised if other researchers argue for shifting the boundaries based on further research. “But most would agree with the general theme that we are pushing very hard on the Earth system, so hard that we should not be surprised if key parts begin to break.”

More from Yale e360

As Climate Warms, Species May Need to Migrate or Perish
With global warming pushing some animals and plants to the brink of extinction, Carl Zimmer writes that conservation biologists are now saying that the only way to save some species may be to move them.

With Temperatures Rising,
Here Comes ‘Global Weirding’
They’re calling it “global weirding” — the way in which rising temperatures are causing species to change their ranges, the timing of their migrations, and the way they interact with other living things. And the implications of all this are only beginning to be understood.
Other researchers agree with the basic concept of the new paper, but question whether we should be trying to pin down planetary boundaries. Michael Mann, a climate scientist at Penn State University, agrees that there probably is a dangerous threshold for climate change, but he thinks that 350 ppm might be too strict a limit. And on a practical level, Mann points out that the policies being considered by the U.S. Congress probably won’t even be able to keep carbon dioxide levels down to 550 ppm in 2100. “I sometimes worry that there is the danger that if we dramatically move the goalposts and argue that 350 ppm must be the stabilization target, policymakers will just throw their hands up in futility,” says Mann, or reach instead for a quick-fix geoengineering scheme, “which frankly terrifies me.”

But some critics question the basic concept itself. “The notion of a single boundary is just devoid of serious content,” says Stuart Pimm. “In what way is an extinction rate 10 times the background rate acceptable?”

One reason that the concept of planetary boundaries is so provocative is that it highlights how much scientists don’t yet understand about the thresholds built into our planet. “I think this is interesting and I’m glad the paper is coming out,” says Naeem, “but it could lead to the false sense that we understand the biosphere better than we do.”

Link:  http://www.e360.yale.edu/content/feature.msp?id=2192

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Gavin Schmidt, Real Climate: PETM Weirdness

PETM Weirdness

Real Climate — Gavin Schmidt, 10 August 2009

The Paleocene-Eocene Thermal Maximum (PETM) was a very weird period around 55 million years ago. However, the press coverage and discussion of a recent paper on the subject was weirder still.

For those of you not familiar with this period in Earth’s history, the PETM is a very singular event in the Cenozoic (last 65 million years). It was the largest and most abrupt perturbation to the carbon cycle over that whole period, defined by an absolutely huge negative isotope spike (> 3 permil in 13C). Although there are smaller analogs later in the Eocene, the size of the carbon flux that must have been brought into the ocean/atmosphere carbon cycle in that one event, is on a par with the entire reserve of conventional fossil fuels at present. A really big number – but exactly how big?

The story starts off innocently enough with a new paper by Richard Zeebe and colleagues in Nature Geoscience to tackle exactly this question. They use a carbon cycle model, tuned to conditions in the Paleocene, to constrain the amount of carbon that must have come into the system to cause both the sharp isotopic spike and a very clear change in the “carbonate compensation depth” (CCD) – this is the depth at which carbonates dissolve in sea water (a function of the pH, pressure, total carbon amount, etc.). There is strong evidence that the the CCD rose hundreds of meters over the PETM – causing clear dissolution events in shallower ocean sediment cores. What Zeebe et al. come up with is that around 3000 Gt carbon must have been added to the system – a significant increase on the original estimates of about half that much made a decade or so ago, though less than some high end speculations.

Temperature changes at the same time as this huge carbon spike were large, too. Note that this is happening on a Paleocene background climate that we don’t fully understand either – the polar amplification in very warm paleo-climates is much larger than we’ve been able to explain using standard models. Estimates range from 5 to 9 °C warming (with some additional uncertainty due to potential problems with the proxy data) – smaller in the tropics than at higher latitudes.

Putting these two bits of evidence together is where it starts to get tricky.

First of all, how much does atmospheric CO2 rise if you add 3000 GtC to the system in a (geologically) short period of time? Zeebe et al. did this calculation and the answer is about 700 ppmv – quite a lot eh? However, that is a perturbation to the Paleocene carbon cycle – which they assume has a base CO2 level of 1000 ppm, and so you only get a 70% increase – i.e., not even a doubling of CO2. And since the forcing that goes along with an increase in CO2 is logarithmic, it is the percent change in CO2 that matters rather than the absolute increase. The radiative forcing associated with that is about 2.6 W/m². Unfortunately, we don’t (yet) have very good estimates of background CO2 levels in Paleocene. The proxies we do have suggest significantly higher values than today, but they aren’t precise. Levels could have been less than 1000 ppm, or even significantly more.

If (and this is a key assumption that we’ll get to later) this was the only forcing associated with the PETM event, how much warmer would we expect the planet to get? One might be tempted to use the standard ‘Charney’ climate sensitivity (2-4.5 ºC per doubling of CO2) that is discussed so much in the IPCC reports. That would give you a mere 1.5-3 ºC warming, which appears inadequate. However, this is inappropriate for at least two reasons. First, the Charney sensitivity is a quite carefully defined metric that is used to compare a certain class of atmospheric models. It assumes that there are no other changes in atmospheric composition (aerosols, methane, ozone) and no changes in vegetation, ice sheets or ocean circulation. It is not the warming we expect if we just increase CO2 and let everything else adjust.

In fact, the concept we should be looking at is the Earth System Sensitivity (a usage I am trying to get more widely adopted) as we mentioned last year in our discussion of ‘Target CO2‘. The point is that all of those factors left out of the Charney sensitivity are going to change, and we are interested in the response of the whole Earth System – not just an idealised little piece of it that happens to fit with what was included in GCMs in 1979.

Now for the Paleocene, it is unlikely that changes in ice sheets were very relevant (there weren’t any to speak of). But changes in vegetation, ozone, methane and aerosols (of various sorts) would certainly be expected. Estimates of the ESS taken from the Pliocene, or from the changes over the whole Cenozoic, imply that the ESS is likely to be larger than the Charney sensitivity since vegetation, ozone and methane feedbacks are all amplifying. I’m on an upcoming paper that suggests a value about 50% bigger, while Jim Hansen has suggested a value about twice as big as Charney. That would give you an expected range of temperature increases of 2-5 ºC (our estimate) or 3-6 ºC (Hansen) (note that uncertainty bands are increasing here, but the ranges are starting to overlap with the observations). All of this assumes that there are no huge non-linearities in climate sensitivity in radically different climates – something we aren’t at all sure about either.

But let’s go back to the first key assumption – that CO2 forcing is the only direct impact of the PETM event. The source of all this carbon has to satisfy two key constraints – it must be from a very depleted biogenic source and it needs to be relatively accessible. The leading candidate for this is methane hydrate – a kind of methane ice that is found in cold conditions and under pressure on continental margins – often capping large deposits of methane gas itself. Our information about such deposits in the Paleocene is sketchy to say the least, but there are plenty of ideas as to why a large outgassing of these deposits might have occurred (tectonic uplift in the proto-Indian ocean, volcanic activity in the North Atlantic, switches in deep ocean temperature due to the closure of key gateways into the Arctic, etc.).

Putting aside the issue of the trigger though, we have the fascinating question of what happens to the methane that would be released in such a scenario. The standard assumption (used in the Zeebe et al. paper) is that the methane would oxidise (to CO2) relatively quickly, and so you don’t need to worry about the details. But work that Drew Shindell and I did a few years ago suggested that this might not quite be true. We found that atmospheric chemistry feedbacks in such a circumstance could increase the impact of methane releases by a factor of 4 or so. While this isn’t enough to sustain a high methane concentration for tens of thousands of years following an initial pulse, it might be enough to enhance the peak radiative forcing if the methane was being released continuously over a few thousand years. The increase in the case of a 3000-GtC pulse would be on the order of a couple of W/m2 – for as long as the methane was being released. That would be a significant boost to the CO2-only forcing given above – and enough (at least for relatively short parts of the PETM) to bring the temperature and forcing estimates into line.

Of course, much of this is speculative given the difficulty in working out what actually happened 55 million years ago. The press response to the Zeebe et al. paper was, however, very predictable.

The problems probably started with the title of the paper “Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming” which on its own might have been unproblematic. However, it was paired with a press release from Rice University that was titled “Global warming: Our best guess is likely wrong,” containing the statement from Jerry Dickens that “There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models.”

Since the know-nothings agree one hundred per cent with these two last statements, it took no time at all for the press release to get passed along by Marc Morano, posted on Drudge, and declared the final nail in the coffin for ‘alarmist’ global warming science on WUWT (Andrew Freedman at WaPo has a good discussion of this). The fact that what was really being said was that climate sensitivity is probably larger than produced in standard climate models seemed to pass almost all of these people by (though a few of their more astute commenters did pick up on it). Regardless, the message went out that ‘climate models are wrong’ with the implicit sub-text that current global warming is nothing to worry about. Almost the exact opposite point that the authors wanted to make (another press release from U. Hawaii was much better in that respect).

What might have been done differently?

First off, headlines and titles that simply confirm someone’s prior belief (even if that belief is completely at odds with the substance of the paper) are a really bad idea. Many people do not go beyond the headline – they read it, they agree with it, they move on. Also one should avoid truisms. All ‘models’ are indeed wrong – they are models, not perfect representations of the real world. The real question is whether they are useful – what do they underestimate? overestimate? and are they sufficiently complete? Thus a much better title for the press release would have been more specific “”Global warming: Our best guess is likely too small” – and much less misinterpretable!

Secondly, a lot of the confusion is related to the use of the word ‘model’ itself. When people hear ‘climate model,’ they generally think of the big ocean-atmosphere models run by GISS, NCAR or Hadley Centre, etc., for the 20th Century climate and for future scenarios. The model used in Zeebe et al. was not one of these, instead it was a relatively sophisticated carbon cycle model that tracks the different elements of the carbon cycle, but not the changes in climate. The conclusions of the study related to the sensitivity of the climate used the standard range of sensitivities from IPCC TAR (1.5-4.5 ºC for a doubling of CO2), which have been constrained – not by climate models – but by observed climate changes. Thus nothing in the paper related to the commonly accepted ‘climate models’ at all, yet most of the commentary made the incorrect association.

To summarise, there is still a great deal of mystery about the PETM – the trigger, where the carbon came from and what happened to it – and the latest research hasn’t tied up all the many loose ends. Whether the solution lies in something ‘fundamental’ as Dickens surmises (possibly related to our basic inability to explain the latitudinal gradients in any of the very warm climates), or whether it’s a combination of a different forcing function combined with more inclusive ideas about climate sensitivity, is yet to be determined. However, we can all agree that it remains a tantalisingly relevant episode of Earth history.

Comments (pop-up) (71)

Link: http://www.realclimate.org/index.php/archives/2009/08/petm-weirdness/

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Kingsford & Brierley: Man-made carbon emissions impacting ocean ecosystems and threatening human food security

Humans 'damaging the oceans' in profound ways

ScienceDaily, August 11, 2009 — There is mounting evidence that human activity is changing the world’s oceans in profound and damaging ways.

Man-made carbon emissions “are affecting marine biological processes from genes to ecosystems over scales from rock pools to ocean basins, impacting ecosystem services and threatening human food security,” the study by Professor Mike Kingsford of the ARC Centre of Excellence for Coral Reef Studies and James Cook University and colleague Dr Andrew Brierley of St Andrews University, Scotland, warns.

A new review, published in the latest issue of the journal Current Biology, says that rates of physical change in the oceans are unprecedented in some cases, and change in ocean life is likely to be equally quick.

These include changes in the areas fish and other sea species can inhabit, invasions, extinctions and major shifts in marine ecosystems.

“In the past, the boundaries between geological ages are marked by sudden losses of species. We may now be entering a new age in which climate change and other human-caused factors such as fishing are the major threats for the oceans and their life,” Andrew and Mike say.

“Given how essential the oceans are to how our entire planet functions it is vital that we intervene before more tipping points are passed and the oceans go down the sort of spiral of decline we have seen in the world’s tropical forests and rangelands, for example.”

Man-made carbon emissions are now above the ‘worst case’ scenario envisioned by the Intergovernmental Panel on Climate Change (IPCC), causing the most rapid global warming seen since the peak of the last Ice Age. At the same time the carbon is acidifying the oceans, with harmful consequences for certain plankton and shellfish.

“At current emission rates it is possible we will pass the critical level of 450 parts per million CO2 in the atmosphere by 2040. That’s the level when, it is generally agreed, global climate change may become catastrophic and irreversible,” they add. “At that point we can expect to see the loss of most of our coral reefs and the arctic seas.”

“The climate is currently warming faster than the worst case known from the fossil record, about 56 million years ago, when temperatures rose about 6 degrees over 1000 years. If emissions continue it is not unreasonable to expect … warming of 5.5 degrees by the end of this century.”

Scientists expect ocean oxygen levels to decline by about six per cent for every one degree increase in temperature and areas in the sea which are low in oxygen to grow by at least 50 per cent. This has major implications for the world’s most productive fishing waters in the cool temperate regions. The seas provide around one sixth of humanity’s protein food – and any loss in fisheries production will have a direct impact on us, he adds.

Besides the changes induced by carbon emissions, the oceans are also under assault from over-fishing, increased UV exposure, toxic pollution, alien species and disease. The combined effect is to weaken the ability of many species to withstand these multiple stresses.

Another risk is that warming will unlock vast reserves of frozen methane in the seabed, triggering uncontrollable, runaway global warming.

“In the face of such terrifying changes even large scale interventions such as establishment of very large networks of Marine Protected Areas are unlikely to be effective,” Mike cautions. “On a global scale, an immediate reduction in CO2 emissions is essential to minimize future human-induced climate change.”

The oceans can also play a role in the proposed solution of eliminating carbon emissions, by producing clean energy from wind, wave and tide – potentially – by triggering phytoplankton blooms with fertilisers to absorb more carbon from the atmosphere, or using the seabed to store CO2. However these require far more research to be sure.

“It may already be too late to avoid major irreversible changes to many marine ecosystems. As history has shown us, these marine-based changes could have major earth-system consequences,” the scientists conclude.

  1. Andrew S. Brierley & Michael J. Kingsford (2009). Impacts of climate change on marine organisms and ecosystems. Current Biology, DOI: 10.1016/j.cub.2009.05.046

Link: http://www.sciencedaily.com/releases/2009/07/090729092538.htm

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R.E. Zeebe, J.C. Zachos, G.R. Dickens, Nature Geosci.,Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming

Nature Geoscience, published online 13 July 2009; doi:10.1038/ngeo578

Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming

Richard E. Zeebe* (School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawaii at Manoa, 1000 Pope Road, MSB 504, Honolulu, HI 96822, U.SA.), James C. Zachos (Earth and Planetary Sciences Department, University of California, Santa Cruz, CA 95064, U.S.A.) and Gerald R. Dickens (Department of Earth Sciences, Rice University, Houston, TX 77005, U.S.A.)

Abstract

The Palaeocene–Eocene Thermal Maximum (about 55 Myr ago) represents a possible analogue for the future and thus may provide insight into climate system sensitivity and feedbacks1, 2. The key feature of this event is the release of a large mass of 13C-depleted carbon into the carbon reservoirs at the Earth's surface, although the source remains an open issue3, 4. Concurrently, global surface temperatures rose by 5–9 °C within a few thousand years5, 6, 7, 8, 9. Here we use published palaeorecords of deep-sea carbonate dissolution10, 11, 12, 13, 14 and stable carbon isotope composition10, 15, 16, 17 along with a carbon cycle model to constrain the initial carbon pulse to a magnitude of 3,000 Pg C or less, with an isotopic composition lighter than -50permil. As a result, atmospheric carbon dioxide concentrations increased during the main event by less than about 70% compared with pre-event levels. At accepted values for the climate sensitivity to a doubling of the atmospheric CO2 concentration1, this rise in CO2 can explain only between 1 and 3.5 °C of the warming inferred from proxy records. We conclude that in addition to direct CO2 forcing, other processes and/or feedbacks that are hitherto unknown must have caused a substantial portion of the warming during the Palaeocene–Eocene Thermal Maximum. Once these processes have been identified, their potential effect on future climate change needs to be taken into account.

*Correspondence, e-mail: zeebe@soest.hawaii.edu

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James Hrynyshyn: Gaps in climate knowledge! Oh no!

Gaps in climate knowledge! Oh no!

Category: climate
Posted on: July 17, 2009, 7:34 a.m., by James Hrynyshyn, The Island of Doubt blog, scienceblogs.com

ResearchBlogging.orgIf predicting climate trends was as easy as predicting the reaction of global warming pseudoskeptics there wouldn't be any deniers left. When I came across a new study in Nature Geoscience on the cause of the massive shift in the climate 55 million years ago, my first reaction was, "How long will it take before someone completely misrepresents this paper as evidence that undermines anthropogenic global warming?"

Not long. See here, here and here, if you have the time.

In the paper, Richard E. Zeebe of the School of Ocean and Earth Science and Technology at the University of Hawaii and his colleagues use some clever isotopic analysis techniques to determine how much carbon was released during the Paleocene-Eocene thermal maximum (PETM) ... I'll let David J. Beerling of the University of Sheffield explain it, as he does in an accompanying essay in Nature Geoscience:

Global warming 55 million years ago was accompanied by a massive injection of carbon into the ocean-atmosphere system, but the resulting climatic warming was much greater than expected from the modeled rise in atmospheric carbon dioxide alone.

Which means our models, the ones forecasting disastrous rises in global average temperatures as soon as the middle of this century if we don't stop pouring more carbon into the ecosystem, aren't up to the task yet of explaining what happened millions of years ago. Does this mean that the world isn't going to warm as much as we feared? Although pseudoskeptical blogospheric reaction would have you answer in the affirmative, the correct response is no. And here's why.

Anyone who has actually read the paper or the essay would understand that the research in question hasn't produced any evidence that would make us rethink the basic idea that more carbon in the air traps more heat. All it does challenge is the completeness of our models. Zeebe et al.'s analysis still finds that massive amounts of carbon-containing molecules found their way into the atmosphere and oceans, precipitating an extreme increase in temperature -- something like 7 or 9 °C -- in a relatively short timespan.

What we still don't know is where all that carbon came from. The resulting warming was twice what we would have expected from carbon dioxide levels alone. As Zeebe and company write:

The origin of this additional warming is unknown at present. Possible causes of the excess warming include increased production and levels of trace greenhouse gases as a consequence of the climatic warming (CH4) [methane].

Beerling, who is better positioned to extrapolate than I, offers "the release of large quantities of methane." What he's talking about are frozen hydrates -- or clathrates -- which are abundant on Earth, largely buried beneath the Arctic permafrost and seabed. If they thaw thanks to global warming, the result would a positive feedback loop in which the carbon from the carbon dioxide initiates the release of more carbon in the form of methane from the clathrates. And then you do see the kind of temperature increase inferred from the isotopic analysis. As Beerling ads:

The total mass of carbon involved in the PETM warming event is uncertain, but some estimates suggest it is roughly equivalent to that stored in fossil fuels (3,000-4,000 Pg C), heightening the relevance of the PETM to present-day climate concerns.

The Zeebe paper is forced to make many assumptions, and some of those assumptions may prove unwarranted. For example, it assumes that the climate response to a doubling of CO2 concentrations is the same regardless of the starting point for CO2 concentrations. Given the role of tipping points, that may be prove to just plain wrong.

Furthermore, this is just one paper, after all. And it hasn't had time to be digested by the entire climatology community. It could be that another few studies will come to opposite conclusions -- that our models do explain what happened 55 million years ago.

But the point is, Zeebe et al. haven't discovered some flaw the basic physics, only a shortcoming in our models' assumptions about the source of carbon-induced warming and the role of positive feedbacks. If anything, what they've found is quite worrisome. If the Beerling's conjecture about feedbacks is correct, then we could be looking at twice the warming hitherto expected this century. (Remember that a global rise of just 2 °C above pre-industrial levels is considered disastrous enough for the world to agree to try to keep things below that.)

Also, just because we don't understand what happened 55 million years ago perfectly, that's no reason to get complacent. The Earth was largely ice-free at the time. CO2 levels were three times higher than today's even before the subsequent spike. So although it's important to understand what happened then, because it's one of the few times the planet has experienced something sort of similar to what's going on now, there are limits to the analogy.

We are going where no one has gone before. The real take-home message from this paper is this: anyone who says the science is settled and we don't need to be spending any more money on such research is just plain wrong.

Zeebe, R., Zachos, J., & Dickens, G. (2009). Carbon dioxide forcing alone insufficient to explain Palaeocene-Eocene Thermal Maximum warming Nature Geoscience, DOI: 10.1038/ngeo578

Link to blog: http://scienceblogs.com/islandofdoubt/2009/07/gaps_in_climate_knowledge_oh_n.php

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Z. Liu et al., Science, 325 (July 17, 2009), Transient simulation of last deglaciation with a new mechanism for Bølling-Allerød Warming

Science (17 July 2009): Vol. 325, No. 5938, pp. 310-314; DOI: 10.1126/science.1171041

Transient simulation of last deglaciation with a new mechanism for Bølling-Allerød Warming

Z. Liu,1,2,3,* B. L. Otto-Bliesner,4 F. He,3 E. C. Brady,4 R. Tomas,4 P. U. Clark,5 A. E. Carlson,6 J. Lynch-Stieglitz,7 W. Curry,8 E. Brook,5 D. Erickson,9 R. Jacob,10 J. Kutzbach,3 and J. Cheng1,3

Abstract

We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO2 forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot.

*Correspondence, e-mail: zliu3@wisc.edu

See link to abstract for authors' affiliations.

Link to abstract: http://www.sciencemag.org/cgi/content/abstract/sci;325/5938/310

Link to full article (subscription required): http://www.sciencemag.org/cgi/content/full/sci;325/5938/273

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Z. Liu & B. Otto-Bliesner: Oak Ridge Supercomputers Provide First Simulation of Abrupt Climate Change

Oak Ridge Supercomputers Provide First Simulation of Abrupt Climate Change

Published on 16 July 2009, 12:04; last update: 17 hour(s) ago by Insciences

OAK RIDGE, Tenn., July 16, 2009 — At the Department of Energy's Oak Ridge National Laboratory (ORNL), the world's fastest supercomputer for unclassified research is simulating abrupt climate change and shedding light on an enigmatic period of natural global warming in Earth's relatively recent history. The work, led by scientists at the University of Wisconsin and the National Center for Atmospheric Research (NCAR), is featured in the July 17, 2009, issue of the journal Science and provides valuable new data about the causes and effects of global climate change.

This research is funded by the Office of Biological and Environmental Research within DOE's Office of Science and by the National Science Foundation through its paleoclimate program and support of NCAR.

In Earth's 4.5-billion-year history, its climate has oscillated between hot and cold. Today our world is relatively cool, resting between ice ages. Variations in planetary orbit, solar output, and volcanic eruptions all change Earth's temperature. Since the Industrial Revolution, however, humans have probably warmed the world faster than nature has. The greenhouse gases we generate by burning fossil fuels and forests will raise the average global temperature 2-12 °F (1-6 °C) this century, the Intergovernmental Panel on Climate Change (IPCC) estimates.

Most natural climate change has taken place over thousands or even millions of years. But an episode of abrupt climate change occurred over centuries—possibly decades—during Earth's most recent period of natural global warming, called the Bolling-Allerod warming. Approximately 19,000 years ago, ice sheets started melting in North America and Eurasia. By 17,000 years ago, the melting glaciers had dumped so much freshwater into the North Atlantic that it stopped the overturning ocean circulation, which is driven by density gradients caused by influxes of freshwater and surface heat. This occurrence led to a cooling in Greenland called the Heinrich event 1. The freshwater flux continued on and off until about 14,500 years ago, when it virtually stopped. Greenland's temperature then rose by 27 °F (15 °C) in several centuries, and the sea level rose about 16 ft. (5 m). The cause of this dramatic Bolling-Allerod warming has remained a mystery and source of intense debate.

"Now we are able to simulate these transient events for the first time," says Zhengyu Liu, a University of Wisconsin professor of atmospheric and oceanic sciences and environmental studies whose team simulated the abrupt climate changes using DOE supercomputers at ORNL. The Oak Ridge Leadership Computing Facility allocated supercomputing time through DOE's Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. "It represents so far the most serious validation test of our model capability for simulating large, abrupt climate changes, and this validation is critical for us to assess the model's projection of abrupt changes in the future," according to Liu.

The Oak Ridge Leadership Computing Facility is funded by the Office of Advanced Scientific Computing Research in DOE's Office of Science.

Liu, director of the University of Wisconsin's Center for Climatic Research, and his collaborator Bette Otto-Bliesner, an atmospheric scientist and climate modeler at NCAR, lead an interdisciplinary, multi-institution research group attempting the world's first continuous simulation of 21,000 years of Earth's climate history, from the last glacial maximum to the present, in a state-of-the-art climate model. The group will also extend the simulation 200 years into the future to forecast climate. The findings could provide great insight into the fate of ocean circulation in light of continued glacial melting in Greenland and Antarctica.

Three parts to abrupt change

Most climate simulations in comprehensive climate models so far are discontinuous, amounting to snapshots of century-sized time slices taken every 1,000 years or so. Such simulations are incapable of simulating abrupt transitions occurring on centennial or millennial timescales. Liu and Otto-Bliesner employ petascale supercomputers, capable of a quadrillion calculations each second, to stitch together a continuous stream of global climate snapshots and recover the virtual history of global climate in a motion picture. They use the Community Climate System Model (CCSM), a global climate model that includes coupled interactions between atmosphere, oceans, lands, and sea ice developed with primary funding from the National Science Foundation (NSF) and DOE.

Based on insights gleaned from their continuous simulation, Liu and his colleagues propose a novel mechanism to explain the Bolling-Allerod warming observed in Greenland ice cores. The three-part mechanism they suggest matches the climate record.

First, one-third of the warming, or 9 °F (5 °C), resulted from a 45 ppm increase in the atmospheric concentration of carbon dioxide, the scientists posit. The cause of the carbon dioxide increase, however, is still a topic of active research, Liu says.

Second, another one-third of the warming was due to recovery of oceanic heat transport. When fresh meltwater flowed off the ice sheet, it stopped the overturning ocean current and in turn the warm surface current from low latitudes, leading to a cooling in the North Atlantic and nearby region. When the melting ice sheet was no longer dumping freshwater into the North Atlantic, the region began to heat up.

The last one-third of the temperature rise resulted from an overshoot of the overturning circulation. "Once the glacial melt stopped, the enormous subsurface heat that had accumulated for 3,000 years erupted like a volcano and popped out over decades," Liu hypothesizes. "This huge heat flux melted the sea ice and warmed up Greenland."

Liu and Otto-Bliesner's collaborators include Feng He, a doctoral student at the University of Wisconsin-Madison who is mainly responsible for the deglaciation modeling, as well as ocean modeler Esther Brady (NCAR), atmospheric scientist Robert Tomas (NCAR), glaciologists Peter Clark (Oregon State University) and Anders Carlson (University of Wisconsin-Madison), paleoceanographers Jean Lynch-Stieglitz (Georgia Institute of Technology) and William Curry (Woods Hole Oceanographic Institution), geochemist Edward Brook (Oregon State University), atmospheric modeler David Erickson (ORNL), computing expert Robert Jacob (Argonne National Laboratory), and climate modelers John Kutzbach (University of Wisconsin-Madison) and Jun Cheng (Nanjing University of Information Science and Technology). "This interdisciplinary team, each member contributing to a different aspect of the project, ranging from a proxy data interpretation to supercomputing coding, has been essential for the success of this project," says Liu.

The 2008 simulations ran on a Cray X1E supercomputer named Phoenix and an even faster Cray XT system called Jaguar. The scientists used nearly a million processor hours in 2008 to run one-third of their simulation, from 21,000 years ago—the most recent glacial maximum—to 14,000 years ago—the planet's most recent major period of natural global warming. With 4 million INCITE processor hours allocated on Jaguar for 2009, 2010, and 2011, they will complete the simulation, capturing climate from 14,000 years ago to the present and projecting it 200 years into the future. "This has been a dream run of both of ours for a long time," says Otto-Bliesner. "This was an opportunity to take advantage of the CCSM, the computing facility at Oak Ridge, and the INCITE call for proposals." No other research group has successfully simulated such a long period in a comprehensive climate model.

Science-based forecasts

More accurately depicting the past means clearer insights into climate's outlook. "The current forecast predicts the ocean overturning current is likely to weaken but not stop over the next century," Liu says. "However, it remains highly uncertain whether abrupt changes will occur in the next century because of our lack of confidence in the model's capability in simulating abrupt changes. Our simulation is an important step in assessing the likelihood of predicted abrupt climate changes in the future because it provides a rigorous test of our model against the major abrupt changes observed in the recent past."

In 2004 and 2005, climate simulations on DOE supercomputers contributed data to a repository that scientists worldwide accessed to write approximately 300 journal articles. The published articles were cited in the Fourth Assessment Report of the IPCC, which concluded that global warming is unequivocal and humans have had a substantial role since the mid-20th century.

Liu and Otto-Bliesner's simulations may soon find their way into IPCC's data repository and reports as other groups succeed in continuous simulation of past abrupt climate changes and demonstrate the results are reproducible. The simulations would thus be a resource for the paleo community at large. Meanwhile, Earth's climate continues to prove that change is an eternal constant. Understanding how we affect the rate of change is a grand challenge of our generation. Petascale computing may accelerate answers that in turn inform our policies and guide our actions.

Contact: Dawn Levy, Communications and External Relations, tel.: (865) 576-6448

Source: Oak Ridge National Laboratory (ORNL)

Link to article: http://insciences.org/article.php?article_id=6175

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Australian Dept. of Climate Change report: Faster Change & More Serious Risks by Will Steffen

Dorothy Cutting, Director, West Coast Climate Equity, sent the link to this 60-page pdf file, which is a report by the Australian Government Department of Climate Change, entitled:


This is what she had to say:

"This is a stunning report. How unnerving it is to see climate data from a different perspective; there are so many slides so new to me. A picture being well worth what it is, I’m stalled on the shocking image of projected temperature anomalies in France, the Ukraine and the Sahel. I’ve seen the numbers, of course, but this slide gives this data so much more impact."

Page 5, Figure 1c shows sea level rise.

Page 6, Figure 2a shows rising CO2 correlated with decreasing sea ice.

Lots of figures showing increasing temperatures and droughts.

Figure 23 shows the projected summer temperatures for various geographic locations, like Europe and the Ukraine -- not pleasant reading at all.

From page 32:

"Some of the most striking advances in climate change science over the past three to four years have been made by taking a systems perspective, in which interactions among components of the climate system and feedback processes that highlight potentially important second-order effects have been elucidated.
An example is research on the links between climate change and the Hadley Circulation, and the
implications of these links for storm tracks, regional precipitation patterns, and modes of natural variability such as the El Ni̱o РSouthern Oscillation (Frierson et al. 2007; Lu et al. 2008; Seidel et al. 2008). Much of this new work points in the same direction Рthat as the 21st century progresses, system-level effects will increasingly amplify rather than dampen the human
perturbation of the climate system."

Page 33, Figure 37 shows the Northern Hemisphere and geographic concentrations of permafrost -- yikes!

Anyway, my words cannot describe all of the very well-portrayed information in the many figures. The report is highly readable -- just takes a bit to download, but well worth it.

This report tells it all, very clearly.

Written by fatih al-farahat in , ,


G. Leduc et al., Nature, 445: Moisture transport across Central America as a positive feedback on abrupt climatic changes

Nature 445, 908-911 (22 February 2007); doi:10.1038/nature05578; received 18 October 2006; accepted 4 January 2007.

Moisture transport across Central America as a positive feedback on abrupt climatic changes

Guillaume Leduc, Laurence Vidal, Kazuyo Tachikawa, Frauke Rostek, Corinne Sonzogni, Luc Beaufort and Edouard Bard (CEREGE, UMR6635, CNRS Université Paul Cézanne Aix-Marseille III, Collège de France, Europôle de l'Arbois, BP 80, 13545 Aix-en-Provence Cedex 04, France)

Abstract

Moisture transport from the Atlantic to the Pacific ocean across Central America leads to relatively high salinities in the North Atlantic Ocean1 and contributes to the formation of North Atlantic Deep Water2. This deep water formation varied strongly between Dansgaard/Oeschger interstadials and Heinrich events—millennial-scale abrupt warm and cold events, respectively, during the last glacial period3. Increases in the moisture transport across Central America have been proposed to coincide with northerly shifts of the Intertropical Convergence Zone and with Dansgaard/Oeschger interstadials, with opposite changes for Heinrich events4. Here we reconstruct sea surface salinities in the eastern equatorial Pacific Ocean over the past 90,000 years by comparing palaeotemperature estimates from alkenones and Mg/Ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity. We detect millennial-scale fluctuations of sea surface salinities in the eastern equatorial Pacific Ocean of up to two to four practical salinity units. High salinities are associated with the southward migration of the tropical Atlantic Intertropical Convergence Zone, coinciding with Heinrich events and with Greenland stadials5. The amplitudes of these salinity variations are significantly larger on the Pacific side of the Panama isthmus, as inferred from a comparison of our data with a palaeoclimate record from the Caribbean basin6. We conclude that millennial-scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes, modulating the North Atlantic freshwater budget and hence North Atlantic Deep Water formation.

Correspondence and requests for materials should be addressed to G.L. (e-mail: leduc@cerege.fr) and E.B. (e-mail: bard@cerege.fr).

Link to abstract: http://www.nature.com/nature/journal/v445/n7130/abs/nature05578.html

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Water vapor transfer at Equator to North Atlantic now going to the Pacific side and thence to the Midwest

UPDATE:

Dear Readers,

I am not a scientist -- my bad!!!!

Dear Cassandra,

I think you misunderstood the point of the Nature paper and of the Sciencedaily report, that indeed properly and fairly relates the essential of the original article.

Guillaume

June 26, 2009 10:39 PM
Tenney said...

Yeah, I think I did misunderstand it -- sorry.

Tenney

btw -- that darned Cassandra name has followed me around via yahoo for more than 10 years -- it has nothing to do with this blog but rather with a family financial matter in 1998.

June 27, 2009 9:55 AM


UPDATE: Dear Readers,

I just located the abstract in Nature related to the Science Daily article below, and basically the Science Daily article draws out the wrong info. Please read the abstract in the post above this one.

Dear Readers,

This article focuses on the transfer of water vapor over the Atlantic from the equator during colder climes. Try to read the article from the perspective of hotter climes, thinking of what happens on the Pacific side of Central America. Also note that, this year, the Intertropical Convergence Zone decided not to go north as usual with the solar equator, thus dumping continuous and enormous quantities of rain on northern and northeastern Brazil, flooding some 500,000 people out of their homes. Next, have a look at the water vapor circulation animations at the links below and tell me where the water vapor from the equator is going now. Looks to be leaving the eastern Pacific south of Baja, Mexico, circles over the Midwest, then back down to the equator on the Atlantic side -- not much like the old days, is it?

http://weather.unisys.com/satellite/sat_wv_hem_loop-12.html

http://www.ssec.wisc.edu/data/east/animation/goeseastwv.html

A climate-change amplifying mechanism

ScienceDaily, March 8, 2007 — During the past 90,000 years, there were alternating hot and cold periods lasting several thousand years each which resulted in a modification of global oceanic circulation. With the help of paleoclimatic and paleo-oceanographic indicators, scientists at CEREGE1 have highlighted a feedback mechanism of ocean circulation on the climate which reinforces this heating or cooling. This mechanism relies on a close link between the circulation of the North Atlantic and the tropical hydrology of Central America. This study, published in the February 22, 2007, review edition of Nature, should allow us to better understand and therefore better predict the effects of climate change on oceanic circulation.In the past, major and rapid climatic variations which took place notably during the last glacial period (Heinrich period) disturbed ocean circulation. Climatic archives (marine and lake sediment, polar ice, stalagmites) show the close relationship existing between climatic variations and oceanic circulation. Changes in oceanic circulation in the North Atlantic have influence on a planetary level by affecting, in particular, the water cycle. These changes are accompanied by a shift in the climatic equator which separates the trade wind systems of the two hemispheres: southwards during cold events and northwards during hot ones.

Central America, a narrow continental strip which separates the Atlantic and Pacific oceans, plays a key role in this system. On the Atlantic side surface waters evaporate, which increases salinity. The water vapour is transferred by the trade winds to the Pacific where it is deposited as rain, thus lowering salinity there. This enormous transfer of water (several hundred thousand cubic meters per second) maintains a contrast in salinity between the two oceans. The surface waters of the tropical Atlantic are then transported, via the Gulf Stream, towards the high latitudes where they warm the atmosphere before plunging into the abysses in the convection zones situated in the seas of Norway, Greenland and Labrador. The deep waters formed by this process then flow into the world ocean, purging the North Atlantic of part of its excess salt.

The scientists at CEREGE1 reconstituted the variations in surface water salinity in the area where the water vapour coming from the Atlantic is deposited. To do this they worked on the measurements taken in marine sediments collected in 2002 west of the Isthmus of Panama by the French oceanographic ship, the Marion Dufresne. This study shows that the cold Heinrich periods correspond to increases in salinity in the east Pacific. This is synonymous to a decrease in the transfer of water vapour. By comparing their results to other studies done in the Atlantic sector and in South America, the scientists were able to describe a feedback mechanism which amplified the climatic disturbance. During cold periods the trade winds, loaded with humidity, migrated southwards. Unable to cross the Andes part of the rain, which would normally have lowered the salinity of the East Pacific, fell in the Amazon basin. This feedback had the effect of re-injecting rainwater into the Atlantic, thereby decreasing the ocean's salinity. This water was then transported to the higher latitudes, contributing to the weakening of deep oceanic circulation, thereby reinforcing the cooling above and around the North Atlantic.

Today, the fact that global warming could disturb the water cycle and lead to a slowing down of the North Atlantic circulation is a real subject of concern. Oceanographic data from the last 50 years suggest that hydrographic changes (temperature and salinity), as well as a lessening of the flow of water transported by certain surface and deep-sea marine currents, have already occurred in the North Atlantic. The risk of an even greater variation of oceanic circulation by the end of this century or the beginning of the next needs to be taken seriously and actively studied.

Link to article: http://www.sciencedaily.com/releases/2007/02/070226131713.htm

Written by fatih al-farahat in


Greenland ice core analysis shows drastic climate change near end of last ice age

Greenland ice core analysis shows drastic climate change near end of last ice age

ScienceDaily (June 19, 2008) — Information gleaned from a Greenland ice core by an international science team shows that two huge Northern Hemisphere temperature spikes prior to the close of the last ice age some 11,500 years ago were tied to fundamental shifts in atmospheric circulation.

The ice core showed the Northern Hemisphere briefly emerged from the last ice age some 14,700 years ago with a 22 °F spike in just 50 years, then plunged back into icy conditions before abruptly warming again about 11,700 years ago. Startlingly, the Greenland ice core evidence showed that a massive "reorganization" of atmospheric circulation in the Northern Hemisphere coincided with each temperature spurt, with each reorganization taking just one or two years, said the study authors.

The new findings are expected to help scientists improve existing computer models for predicting future climate change as increasing anthropogenic greenhouse gases in the atmosphere drive up Earth's temperatures globally.

The team used changes in dust levels and stable water isotopes in the annual ice layers of the two-mile-long Greenland ice core, which was hauled from the massive ice sheet between 1998 and 2004, to chart past temperature and precipitation swings. Their paper was published in the June 19, 2008, issue of Science Express, the online version of Science.

The ice cores -- analyzed with powerful microscopes -- were drilled as part of the North Greenland Ice Core Project led by project leader Dorthe Dahl-Jensen of the Centre for Ice and Climate at the Neils Bohr Institute of the University of Copenhagen. The study included 17 co-investigators from Europe, one from Japan and two from the United States -- Jim White and Trevor Popp from the University of Colorado at Boulder.

"We have analyzed the transition from the last glacial period until our present warm interglacial period, and the climate shifts are happening suddenly, as if someone had pushed a button," said Dahl-Jenson.

According to the researchers, the first abrupt warming period beginning at 14,700 years ago lasted until about 12,900 years ago, when deep-freeze conditions returned for about 1,200 years before the onset of the second sharp warming event. The two events indicate a speed in the natural climate change process never before seen in ice cores, said White, director of CU-Boulder's Institute for Arctic and Alpine Research.

"We are beginning to tease apart the sequence of abrupt climate change," said White, whose work was funded by the National Science Foundation's Office of Polar Programs. "Since such rapid climate change would challenge even the most modern societies to successfully adapt, knowing how these massive events start and evolve is one of the most pressing climate questions we need to answer."

Both dramatic warming events were preceded by decreasing Greenland dust deposition, indicating higher tropical temperatures and significantly more rain falling on the deserts of Asia at the time, said White. The team believes the ancient tropical warming caused large, rapid atmospheric changes at the equator, the intensification of the Pacific monsoon, sea-ice loss in the north Atlantic Ocean and more atmospheric heat and moisture over Greenland and much of the rest of the Northern Hemisphere.

"Here we propose a series of events beginning in the lower latitudes and leading to changes in the ocean and atmosphere that reveal for the first time the anatomy of abrupt climate change," the authors wrote. White likened the abrupt shift in the Northern Hemisphere circulation pattern to shifts in the North American jet stream as it steers storms around the continent.

"We know such events are in Earth's future, but we don't know when," said White. "One question is whether we can see the symptoms before big problems occur. Until we answer these questions, we are speeding blindly down a narrow road, hoping there are no curves ahead."

Each yearly record of ice can reveal past temperatures and precipitation levels, the content of ancient atmospheres and even evidence for the timing and magnitude of distant storms, fires and volcanic eruptions, said White. The cores from the site -- located roughly in the middle of Greenland at an elevation of about 9,850 ft. -- are 4-in. diameter cylinders brought to the surface in 11.5-ft. lengths, said White.

Link to article: http://www.sciencedaily.com/releases/2008/06/080619142112.htm