Showing posts with label Little Ice Age. Show all posts

Written by fatih al-farahat in ,


John Cook: A South American hockey stick

A South American hockey stick

by John Cook, Skeptical Science, September 18, 2010
A new paper has just been published employing a new technique for reconstructing past temperatures (Kellerhals 2010). It uses ammonium concentration from an ice core in tropical South America (the eastern Bolivian Andes) as a proxy for temperature. This enables them to build a temperature record going back 1600 years in a region which has had little proxy data available until now. They find a distinguishable Medieval Warm Period and Little Ice Age in the record. Nevertheless, they also find the last few decades show unprecedented warmth over the last 1600 years. 

Figure 1. Reconstructed tropical South American temperature anomalies (normalized to the 1961–1990 AD average) for the last 1600 years (red curve, smoothed with a 39‐year Gaussian filter). The shaded region envelops the ±2 standard deviation uncertainty as derived from the validation period. Poor core quality precluded any chemical analysis for the time interval between 1580 and 1640 AD.
Note that Figure 1 shows only the proxy record from the ice core -- no instrumental data is included. Of course, the usual caveat applies when looking at a single proxy record -- this is a temperature record for a single location.To get a better feel for past climate, you need to look at proxy records from a range of locations.
When we combine all the various temperature records, we find the same result: modern temperatures are significantly warmer than medieval temperatures. This is demonstrated in Moburg's reconstruction of Northern Hemisphere temperature (which happens to bear a striking resemblance to the South American proxy record). 


Figure 2. Northern Hemisphere Temperature Reconstruction by Moburg et al. (2005) shown in blue, Instrumental Northern Hemisphere Temperatures from Hadley shown in Red. Thanks to Robert Way for providing this graph.

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The upcoming ice age has been postponed indefinitely

The upcoming ice age has been postponed indefinitely

by John Cook, Skeptical Science, January 27th, 2010

The 9th most popular skeptic argument is that we're heading into an ice age. The whole premise of the website Ice Age Now is that a new ice age could begin any day. Considering the skeptic aversion towards alarmism, it's surprising that this idea has gained so much traction. In the interest of lowering skeptics' stress levels, its time to put all those ice age fears to rest once and for all.

Just a few centuries ago, the planet experienced a mild ice age, quaintly dubbed the Little Ice Age. Part of the Little Ice Age coincided with a period of low solar activity termed the Maunder Minimum (named after astronomer Edward Maunder). It's believed that a combination of lower solar output and high volcanic activity were a major contributor (Free 1999, Crowley 2001), with changes in ocean circulation also having an effect on European temperatures (Mann 2002). 

Solar Activity - Total Solar Irradiance (TSI) including Maunder Minimum
Figure 1. Total Solar Irradiance (TSI). TSI from 1880 to 1978 from Solanki. TSI from 1979 to 2009 from PMOD.

Could we be heading into another Maunder Minimum? Solar activity is currently showing a long term cooling trend. 2009 saw solar output at its lowest level in over a century. However, predicting future solar activity is problematic. The transition from a period of 'grand maxima' (the situation in the latter 20th century) to a 'grand minima' (e.g., Maunder Minimum conditions) is a chaotic process and difficult to predict (Usoskin, 2007).
Let's say for the sake of argument that the sun does enter another Maunder Minimum over the next century. What effect would this have on Earth's climate? The difference in solar radiative forcing between Maunder Minimum levels and current solar activity is estimated between 0.17 W/m2 (Wang, 2005) to 0.23 W/m2 (Krivova, 2007). In contrast, the radiative forcing of CO2 since pre-industrial times is 1.66 W/m2 (IPCC AR4), far outstripping solar influence. Add to this the extra CO2 emitted in upcoming decades and other greenhouse gases such as methane. The warming from man-made greenhouse gases far outstrips any potential cooling even if the sun was to return to Maunder Minimum levels.

However, our climate has experienced much more dramatic change than the Little Ice Age. Over the past 400,000 years, the planet has experienced ice age conditions, punctuated every 100,000 years or so by brief warm intervals. These warm periods, called interglacials, typically last around 10,000 years. Our current interglacial began around 11,000 years ago. Could we be on the brink of the end of our interglacial?

Temperature of Vostok, Antarctica including interglacials and Milankovitch cycles
Figure 2. Temperature change at Vostok, Antarctica (Barnola, 2003). Interglacial periods are marked in green.

How do ice ages begin? Changes in the earth's orbit cause less sunlight (insolation) to fall on the northern hemisphere during summer. Northern ice sheets melt less during summer and gradually grow over thousands of years. This increases the Earth's albedo which amplifies the cooling, spreading the ice sheets further. This process lasts around 10,000 to 20,000 years, bringing the planet into an ice age.

Not all interglacials last the same amount of time. An ice core from Dome C, Antarctica offered a glimpse of temperatures going back 720,000 years. Climatic conditions 420,000 years ago were similar to current conditions. At that time, the interglacial lasted 28,000 years, suggesting our current interglacial may have lasted a similar period without human intervention (Augustin, 2004).

The similar conditions between now and 400,000 years ago are due to similar configurations in the Earth's orbit. At both times, the forcing from orbital variations showed much less change then in other interglacials. Simulations with the current orbit find that even without CO2 emissions, the current interglacial is expected to last at least 15,000 years (Berger, 2007).

Of course, the question of how long our interglacial lasts without human intervention is moot. We are intervening. So what effect do our CO2 emissions have on any future ice ages? This question is examined in one study that examines the glaciation "trigger" -- the required drop in summer northern insolation to begin the process of growing ice sheets (Archer 2005). The more CO2 there is in the atmosphere, the lower insolation needs to drop to trigger glaciation.

Figure 3 examines the climate response to various CO2 emission scenarios. The green line is the natural response without CO2 emissions. Blue represents an anthropogenic release of 300 gigatonnes of carbon -- we have already passed this mark. Release of 1000 gigatonnes of carbon (orange line) would prevent an ice age for 130,000 years. If anthropogenic carbon release were 5000 gigatonnes or more, glaciation will be avoided for at least half a million years. As things stand now, the combination of relatively weak orbital forcing and the long atmospheric lifetime of carbon dioxide is likely to generate a longer interglacial period than has been seen in the last 2.6 million years.

Future temperature rise based on various CO2 emission scenarios
Figure 3. Effect of fossil fuel CO2 on the future evolution of global mean temperature. Green represents natural evolution, blue represents the results of anthropogenic release of 300 Gton C, orange is 1000 Gton C, and red is 5000 Gton C (Archer, 2005).
 
So we can rest assured, there is no ice age around the corner. To those with lingering doubts that an ice age might be imminent, turn your eyes towards the northern ice sheets. If they're growing, then yes, the 10,000 year process of glaciation may have begun. However, currently the Arctic permafrost is degrading, Arctic sea ice is melting and the Greenland ice sheet is losing mass at an accelerating rate. These are hardly good conditions for an imminent ice age.

Thanks to John Cross for putting me onto a few very relevant papers while preparing this post.

Link:  http://www.skepticalscience.com/upcoming-ice-age-postponed-indefinitely.html

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Michael E. Mann et al., Science 326 (2009), Global signatures and dynamical origins of the Little Ice Age and Medieval Climate Anomaly

Science (27 November 2009), Vol. 326, No. 5957, pp. 1256-1260; DOI: 10.1126/science.1177303

Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly

Michael E. Mann,1,* Zhihua Zhang,1 Scott Rutherford,2 Raymond S. Bradley,3 Malcolm K. Hughes,4 Drew Shindell,5 Caspar Ammann,6 Greg Faluvegi,5 and Fenbiao Ni4 

Abstract

Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña–like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation–Arctic Oscillation.

*Correspondence e-mail: mann@meteo.psu.edu

Link to abstract:  http://www.sciencemag.org/cgi/content/short/326/5957/1256

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M.M. Fauria et al., Climate Dynamics, Unprecedented low twentieth century winter sea ice extent in the Western Nordic Seas since A.D. 1200

Climate Dynamics (June 23, 2009); DOI: 10.1007/s00382-009-0610-z

Unprecedented low twentieth century winter sea ice extent in the Western Nordic Seas since A.D. 1200

M. Macias Fauria1, 2, 5, 10 Contact Information, A. Grinsted4, 3, S. Helama2, J. Moore3, 6, 7, M. Timonen5, T. Martma9, E. Isaksson8 and M. Eronen2

(1) Biogeoscience Institute, University of Calgary, Calgary, AB, Canada
(2) Department of Geology, University of Helsinki, Helsinki, Finland
(3) Arctic Centre, University of Lapland, Rovaniemi, Finland
(4) Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
(5) Rovaniemi Research Station, Finnish Forest Institute, Rovaniemi, Finland
(6) Thule Institute, University of Oulu, Oulu, Finland
(7) College of Global Change and Earth System Science, Beijing Normal University, Beijing, China
(8) Polar Environmental Centre, Norwegian Polar Institute, Tromsø, Norway
(9) Institute of Geology, Tallinn University of Technology, Tallinn, Estonia
(10) Department of Ecology, Faculty of Biology, University of Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain

(Received 1 October 2008, accepted 9 June 2009, published online 23 June 2009.)

Abstract

We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200–1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ18O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864–1997. The significance of the reconstruction statistics (reduction of error, coefficient of efficiency) is computed for the first time against a realistic noise background. The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid-eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Moderate sea ice extent occurred during thirteenth–fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at ~50–120 year. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.

M. Macias Fauria, e-mail: mmaciasf@ucalgary.ca

Link to abstract: http://www.springerlink.com/content/922v30um17650817/

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Sea Ice July 2009

The areal extent of the sea ice was around a half million square kilometers larger this year than it was over the past four years. However that has abruptly changed and it is almost as low now as 2007. Most interesting this year is that Davis Strait is wide open already and it is also way ahead on the Eastern side by Russia.

http://www.socc.ca/cms/en/socc/seaIce/currentSeaIce.aspx

What appears different this year to this observer is that the polar ice seems more intact for the moment. That means to me that the Northwest Passage may stay sealed. No bets yet.

The period of maximum attack on the ice has begun and it will be interesting to see just how much it opens up.

Do recall that it was reported much thinner than expected earlier this spring, so these pictures may be misleading.

I will say however, that it is very vulnerable to wind activity.

I notice that I can sail deep along the north coast of Greenland for the first time and that Lancaster is already wide open until you hit the end of Ellesmere.

The attached report is important because it discounts the extent of sea ice decline during the medieval warm period. That may be because of proxy failure rather than reality. However, the strong warming in the early part of the twentieth century kicked of an ongoing cycle of ice retreat with modest recoveries. Therefore the net loss over each cycle is positive for one century.

Up to this point, I was only comfortable that that held true for the past three decades or so. Our present decade is only slightly cooler than the past decade, but it is apparent that the trend line on ice loss is still positive.

We are set up right now, should weather cooperate, for another sharp decline in ice thickness this year, at a time in which there is much less to work with. Again the remarkable and unexpected thinness this spring is remarked.

I hate to say this, but we are on track for open water around the pole in 2012. Nothing has reversed the established trend, and this item has established that the condition has persisted over a whole century and losses now are quite visible and reflect expectations of final breakup.

The Least Sea Ice In 800 Years

http://www.terradaily.com/reports/The_Least_Sea_Ice_In_800_Years_999.html

by Staff Writers
Copenhagen, Denmark (SPX) Jul 03, 2009

New research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13th century to the present indicates that there has never been so little sea ice as there is now. The research results from the Niels Bohr Institute, among others, are published in the scientific journal, Climate Dynamics.

There are of course neither satellite images nor instrumental records of the climate all the way back to the 13th century, but nature has its own 'archive' of the climate in both ice cores and the annual growth rings of trees and we humans have made records of a great many things over the years - such as observations in the log books of ships and in harbour records. Piece all of the information together and you get a picture of how much sea ice there has been throughout time.

Modern research and historic records

"We have combined information about the climate found in ice cores from an ice cap on Svalbard and from the annual growth rings of trees in Finland and this gave us a curve of the past climate" explains Aslak Grinsted, geophysicist with the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen.

In order to determine how much sea ice there has been, the researchers needed to turn to data from the logbooks of ships, which whalers and fisherman kept of their expeditions to the boundary of the sea ice. The ship logbooks are very precise and go all the way back to the 16th century.

They relate at which geographical position the ice was found. Another source of information about the ice are records from harbours in Iceland, where the severity of the winters have been recorded since the end of the 18th century.

By combining the curve of the climate with the actual historical records of the distribution of the ice, researchers have been able to reconstruct the extent of the sea ice all the way back to the 13th century. Even though the 13th century was a warm period, the calculations show that there has never been so little sea ice as in the 20th century.

In the middle of the 17th century there was also a sharp decline in sea ice, but it lastet only a very brief period. The greatest cover of sea ice was in a period around 1700-1800, which is also called the 'Little Ice Age'.

"There was a sharp change in the ice cover at the start of the 20th century," explains Aslak Grinsted. He explains, that the ice shrank by 300.000 km2 in the space of ten years from 1910-1920. So you can see that there have been sudden changes throughout time, but here during the last few years we have had some record years with very little ice extent.

"We see that the sea ice is shrinking to a level which has not been seen in more than 800 years", concludes Aslak Grinsted.

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Samuli Helama et al., Multicentennial megadrought in northern Europe coincided with a global ENSO drought pattern during the Medieval Climate Anomaly

Geology, February 2009, Vol. 37, No. 2, 175–178; doi:10.1130/G25329A.1
© 2009 Geological Society of America

Multicentennial megadrought in northern Europe coincided with a global El Niño–Southern Oscillation drought pattern during the Medieval Climate Anomaly

Samuli Helama1, Jouko Meriläinen2 and Heikki Tuomenvirta3

1Department of Geology, P. O. Box 64, 00014 University of Helsinki, 00014 Helsinki, Finland
2SAIMA Unit of Savonlinna Department of Teacher Education, University of Joensuu, P. O. Box 86, 57101 Savonlinna, Finland
3Finnish Meteorological Institute, P. O. Box 503, 00101 Helsinki, Finland

Abstract

The El Niño–Southern Oscillation (ENSO) is a pacemaker of global climate, and the accurate prediction of future climate change requires an understanding of the ENSO variability. Recently, much-debated aspects of the ENSO have included its long-term past and future changes and its associations with the North Atlantic and European sectors, potentially in interaction with the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. Here we present the first European dendroclimatic precipitation reconstruction that extends through the alternating climate phases of the Medieval Climate Anomaly and the Little Ice Age. We show that northern Europe underwent a severe precipitation deficit during the Medieval Climate Anomaly, which was synchronous with droughts in various ENSO-sensitive regions worldwide, while the subsequent centuries during the Little Ice Age were markedly wetter. We attribute this drought primarily to an interaction between the ENSO and the North Atlantic Oscillation, and to a lesser (or negligible) degree to an interaction between the ENSO and the Atlantic Multidecadal Oscillation.

Link to abstract: http://geology.gsapubs.org/cgi/content/abstract/37/2/175