Stuart Gaffin is a climate researcher at Columbia University and a regular contributor with his blog “Exhausted Earth”; this is a reply to a blog by Holman Jenkins, a Wall Street Journal columnist and member of the WSJ editorial board. Thomson Reuters is not responsible for the content -- the views are the author’s alone.

Mr. Jenkins replies that the clarification of his perplexing column is a reiteration of his original sentence “…We don’t really have the slightest idea how an increase in the atmosphere’s component of CO2 is impacting our climate, though the most plausible indication is that the impact is too small to untangle from natural variability…”

He still doesn’t say where his ‘most plausible indication’ comes from except for his reference to some unnamed “…many scientists who have pursued empirical results [that] show the human contribution [has] been …maddeningly elusive or indeterminate.”

By contrast, I have no hesitation to say I was referring to IPCC when quoting the 90% confidence attribution of warming to human activities.

With regard to the first part of his dismissal of the present impact of CO2 on our climate, this has been the focus of core IPCC studies for many years and is called the ‘radiative forcing’ of the atmosphere compared to pre-industrial times (e.g., 1750). This is the energy imbalance created in the atmosphere by a factor such as greenhouse gases, aerosols, solar energy, clouds, and land use. The resulting bar chart (see figure below) is famous. CO2 dominates the chart and is estimated in 2005 to be contributing a +1.66 W/sq. meter positive imbalance, greater than any other forcing, including solar by five times.

The point is Mr. Jenkins says I misread his statement about science not knowing “…how an increase in the atmosphere’s component of CO2 is impacting our climate …” But I responded directly to this claim when I wrote that he is effectively saying we know nothing about how “CO2 affects … Earth’s energy balance” — I was referring to the energy imbalance chart shown above and the +1.66 Watts/square meter forcing.

Also, current warming from CO2 isn’t the only thing we ‘actually care’ about.

Here are at least three other scientific issues and facts about CO2 that will have major implications for society and the environment, even if Mr. Jenkins does not care about them:

(i) How high will CO2 levels go if Mr. Jenkins had his way? 700 ppm? 1000 ppm?

(ii) The atmospheric CO2 excess we are creating will last 100s to 1000s of years into the future

(iii) As excess CO2 dissolves in the oceans. it is acidifying them and will adversely impact marine life worldwide

Since Mr. Jenkins raises the ‘global warming has stopped’ claim, 2008 was the 9th warmest year on record since 1880, and the 10 warmest years on record have occurred between 1997-2008.

Moreover, right now, we are in a cool phase of both the 11-year sunspot cycle and also the cool phase of the powerful oceanic El Nino cycle, so it’s not surprising that the last few years haven’t broken all-time records. The sunspot and El Nino cycles will turn around and warm again.

Meanwhile, CO2 and other greenhouse gases continue to grow unabated.

Mr. Jenkins seems strangely unaware that the warming of the 20th century has coincided with 20th century increases in CO2. Also, the current rates of increases of CO2 and other greenhouse gases are extraordinarily unprecedented during the last 2000 years of human civilization (see figure below), which is no doubt the most important period to consider for modern society.

I called attention to Mr. Jenkins' use of “contribution” because it is a peculiar word to use to describe something that is wholly due to human activities, unless you want to leave the door open in readers' minds that natural emissions are playing a significant role in the observed increases. Skeptics try to confuse the public about this by saying that since natural fluxes of CO2 from the ocean and biosphere are larger than human emissions, our emissions can’t be significant. But these fluxes have been tightly in balance over the last few thousand years, as seen from ice core data for example (below). More importantly, Mr. Jenkins still doesn’t fully acknowledge this fact about the cause of today’s CO2 rise.

Link to article: http://blogs.reuters.com/environment/2009/03/06/wall-street-journal-of-atmospheric-sciences-reply-to-jenkins/