There is an interesting presentation on the weblog Real Climate that illustrates their perspective.
The post is What do climate scientists think? by Gavin Schmidt and Eric Steig .It includes the text
“….For decades, one of the main tools in the arsenal of those seeking to prevent actions to reduce emissions has been to declare the that the science is too uncertain to justify anything. To that end, folks like Fred Singer, Art Robinson, the Cato Institute and the ‘Friends’ of Science have periodically organised letters and petitions to indicate (or imply) that ‘very important scientists’ disagree with Kyoto, or the Earth Summit or Copenhagen or the IPCC etc. These are clearly attempts at ‘arguments from authority’, and like most such attempts, are fallacious and, indeed, misleading.
They are misleading because as anyone with any familiarity with the field knows, the basic consensus is almost universally accepted. That is, the planet is warming, that human activities are contributing to the greenhouse gases in the atmosphere (chiefly, but not exclusively CO2), that these changes are playing a big role in the current warming, and thus, further increases in the levels of GHGs in the atmosphere are very likely to cause further warming which could have serious impacts. You can go to any standard meeting or workshop, browse the abstracts, look at any assessment, ask any of the National Academies etc. and receive the same answer. There are certainly disputes about more detailed or specific issues (as there is in any scientific field), and lots of research continues to improve our quantitative understanding of the system, but the basic issues (as outlined above) are very widely (though not universally) accepted.
The substance of their text involves the statements
- the planet is warming
- that human activities are contributing to the greenhouse gases in the atmosphere
- that human activities are contributing to the greenhouse gases in the atmosphere (chiefly, but not exclusively CO2)
- that these changes are playing a big role in the current warming
- further increases in the levels of GHGs in the atmosphere are very likely to cause further warming which could have serious impacts
The first item, the climate system warmed during the 20th century is certainly true, although this warming has stalled in the last few years, as documented, for example, on my weblog (e.g. see).
On the second item, this is universally accepted by all in the climate science community. The largest of these human greenhouse gas inputs are from CO2. There is also agreement by most (including myself) that added CO2 is a warming climate forcing and that it is a significant effect (e.g. see my slide 12 ). If the levels of the GHGs become large enough, of course, they exert a larger radiative warming, and this could have negative effects on society and the environment.
Thus, the statements by Gavin and Eric do not address the crux of the disagreement with a number of their colleagues. We agree that added CO2 is AN important (i.e. first order) human climate forcing. However, it is not THE only first order human climate forcing. Moreover, natural climate forcings have become better recognized in the last few years as having significantly larger effect on the climate system than is represented in the IPCC global models (e.g. see and see).
We published our paper
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union
to document where the actual disagreements with colleagues such as Eric Steig ,and particularly Gavin Schmidt, exist (e.g. see also).
We conclude that
“..policies focused on controlling the emissions of greenhouse gases must necessarily be supported by complementary policies focused on other first-order climate forcings.”
These other first order human climate forcings, as we report in our paper, are
“In addition to greenhouse gas emissions, other first-order human climate forcings are
important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role ofchanges in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005]. As with CO2, the lengths of time that they affect the climate are estimated to be on multidecadal time scales and longer.”
Until, and unless, Real Climate can successfully argue why we need to be primarily concerned with CO2, and why the perspective that we present above is incorrect, they are not presenting a “basic consensus is almost universally accepted”.