“Although the current overall capacity for society to perturb the carbon cycle is comparable to that of the PETM [the Paleocene-Eocene Thermal Maximum, 55 million years ago], the rate at which we are imposing the current perturbation on the Earth system may be unprecedented.” Ying Cui et al. 
“The last deglacial transition, although characterized by temperature and CO2-increase, is two orders of magnitude slower than the current anthropogenic change. It is also thought to largely represent a redistribution of carbon within the ocean and to the atmosphere and terrestrial biosphere and hence did not have as potent or globally uniform an acidification effect as an input from geological reserves.” B. Honisch et al .
At a party a few weeks ago a friend identified himself as a moderate claiming to listen to both sides of arguments. I suggested that an issue like illegal immigration has no basis in the hard sciences and therefore on that issue at least a moderate view might make sense but that opinions on either side are likely ideological. I suppose there is a body of historic data or economic analysis but these are subject to cherry picking. Economic analysis is famous for being capable of deriving any desired result and history is a soft science. But the issue of anthropogenic global warming is different. Global warming is founded on hard science by experimentation, observation and analysis and has been developed using the scientific method and is therefore quite rigorous. Thus the truth is knowable with reasonably good approximation. I reminded my friend of Nobel Laureate Physicist Richard Feynman’s advice that science is what humans do to keep from lying to ourselves.
To deny global warming is to deny science itself and thus reality and consequently to slide down a slippery slope into a mind space where any inconvenient reality can be denied and all self-deception can be rationalized. Since AGW is an existential issue for the human race denial is a rather big lie and one cannot reasonably assume a denier isn’t also lying about everything else. And reality has to inform the moderate view else it isn’t moderate.
My friend said  “Wait a minute, Tony, there are compelling arguments. After all, the climate has changed in the past without human influence. Consider the ice ages.”
Like all denier arguments, this one is curiously nonsensical. This is easy to appreciate by using the same argument in a different the context. A cigarette smoker informs you that there is no reason for him not to smoke in bed because houses burn down from natural causes. Sure they do but the number one cause of fatal fires is still careless smoking . The possibility of one does not rule out the possibility of the other. In fact, the study of natural house fires reveals just how flammable houses are and how sensitive they are to careless smoking and other human misbehavior. Another salient point is that the scientists, who study one cause, are the same ones who study the other. It is not the case that deniers study natural causes and climate scientists study only human causes. Climate scientists study both while deniers simply make stuff up.
I replied, “Seriously, John? That argument doesn’t make any sense even if you don’t know the science. But the science is that the transition from the depths of the ice age with ice a mile deep over New York to the mild Holocene when humans discovered agriculture and built cities was two orders of magnitude slower than what humans are doing to the climate now; two orders of magnitude slower.”
He looked back at me stunned so I repeated, filling the void, “Two orders of magnitude slower and yet the impact was that dramatic. Did your source forget to mention that not insignificant detail?”
The figure below is from a recent paper by Andrea Burke and Laura Robinson published in the journal Science . The purple curve is a reconstruction of atmospheric carbon dioxide from ice core data stretching back from the last glacial maximum (LGM), 20,000 years ago through the Holocene to the pre-industrial era. I superimposed a box circumscribing the part of the curve which shows the fastest rise in atmospheric carbon dioxide during this time. Atmospheric carbon dioxide increased 30 parts per million by Volume (ppmV) from 17,300 years ago until 16,000 years ago or over a period of 1300 years at the beginning of the shaded Heinrich stadial 1 (HS1). This is equivalent to an average rise of 0.023 ppmV/year over the period of fastest increase. The increase during the Younger Dryas (YD) is almost as steep. Currently, human emissions are increasing atmospheric carbon dioxide by about 2.4 ppmV or one hundred times faster than the most rapid increase during the last deglaciation.
Likewise the global temperature increased about 5 degree Celsius over thousands of years or by the same amount as the projections based on a business-as-usual path for human emissions for just this century . I wanted to ask my friend who he thought was studying paleoclimate if not actual credible climate scientists. Did he think deniers were generating this science? In fact the study of past climate change, paleoclimatology, is of great interest to climate scientists who are desperately looking for analogous events to the current situation. This study will be a significant part of the next Intergovernmental Panel on Climate Change report .
A good recent example is a paper by Barbel Honisch and colleagues  which reviews climate change events of the past 300 million years and concludes that “Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry – a consequence of the unprecedented rapidity of CO2 release currently taking place.” In fact the Permian Triassic extinction event, 252 million years ago may be the closest analogue but it was accompanied by an estimated annual carbon release of between 0.1 and 1 Gigatons per year compared with current human emissions which are 10 Gigatons per year. Yet the End Permian was the most severe of all mass extinction events, extirpating between 90 and 96 percent of all species . We are emitting carbon ten times faster and combining that with a large variety of additional coherent misbehavior such as over fishing, mountaintop removal mining and over fertilization.
Meanwhile about global warming Senator Inhofe said on MSNBC last week in an interview with Rachel Maddow : “I was actually on your side of this issue when I was chairing that committee and I first heard about this. I thought it must be true until I found out what it cost.” In other words, Inhofe decided to deny physical reality because it conflicted with his very bad economics. Demonstrating that he has gone well off the deep end, Inhofe has also said : “The arrogance of people to think that we, human beings, would be able to change what He is doing in the climate is to me outrageous.” Obviously only God can change the climate and start house fires. So according to Inhofe we are all off the hook; liars, murderers, rapists, careless smokers, strip miners, coal companies, Wall Street bankers, corrupt senators, everybody because only God can do anything and if you think your activity has any significance at all, you are just too bloody arrogant. Some theology.
I find it curious that my friend, who is intelligent, would be skeptical of legitimate science while accepting unquestioningly utter nonsense from utterly unreliable people (I assume his source is the main-stream media). Why Inhofe rejects science in favor of nonsense is not nearly as mysterious when we consider that he has received over $1.3 million in campaign contributions from the fossil fuels industry . Money talks and only God can take a bribe.
I’ve pointed out before that the Republican Party institutionally denies climate physics and therefore cannot be trusted on any issue, but heck don’t take my word for it. Ann Coulter  recently said: “I think our party and particularly our movement, the conservative movement, does have more of a problem with con men and charlatans than the Democratic Party.” Dishonesty attracts them like flies.
Dear reader, the climate has indeed changed in the past in ways which have been quite dramatic and on a few occasions even resulting in mass extinctions. And yet the perturbations to the earth system, the forcing functions, have been one or more orders of magnitude slower than what we are doing now in many respects but we are also doing additional things which are unprecedented. What do you think the outcome is going to be? You may want to ask yourselves while looking at your kids and grandkids if Homo sapiens could survive a major mass extinction event, regardless of whether it was caused by God or by our own misbehavior.
And a moderate does not take counsel from con men and charlatans.
 Ying Cui, Lee R. Kump, Andy J. Ridgwell, Adam J. Charles, Christopher K. Junium, Aaron F. Diefendorf, Katherine H. Freeman, Nathan M. Urban and Ian C. Harding, Slow release of fossil carbon during the Palaeocene–Eocene Thermal Maximum, Nature Geoscience, 5 June 2011 | DOI: 10.1038/NGEO1179
 B. Honisch, et al., The Geological Record of Ocean Acidification, Science, vol 335, 2 March, 2012.
 It would not have mattered if my friend had chosen any other denier argument as they are all pretty ludicrous. For a complete list with applicable debunking see http://www.skepticalscience.com/
 Andrea Burke and Laura Robinson, The Southern Ocean’s Role in Carbon Exchange During the Last Deglaciation, Science, vol 335, 3 February 2012. See also Michael Kaplan, et al., Glacier retreat in New Zealand during the Younger Dryas stadial, Vol 467| 9 September 2010| doi:10.1038/nature09313
 James E. Hansen and Makiko Sato, Paleoclimate Implications for Human-Made Climate Change, NASA Goddard Institute for Space Studies and Columbia University Earth Institute, New York. See also the MIT study Sokolov, A. P., and Coauthors, 2009: Probabilistic Forecast for Twenty-First-Century Climate Based on Uncertainties in Emissions (Without Policy) and Climate Parameters. J. Climate, 22, 5175–5204. doi: http://dx.doi.org/10.1175/2009JCLI2863.1 see also http://globalchange.mit.edu/pubs/abstract.php?publication_id=990
 J. Tollefson, “Forecasters look back in time”, Nature, vol 483, 15 March, 2012, also P. Valdes, Built for Stability, Nature Geoscience, vol 4, July 2011, and R. Zeebe, Where are you heading Earth?, in the same issue.
 Michael Benton, When Life Nearly Died, Thames and Hudson 2003, also Douglas Erwin, Extinction, Princeton, 2006.