Climate change (6)

It took me five posts to cover just two topics within the AGW theory – the instrumental temperature record and climate sensitivity. For a more comprehensive summary of the issue, written from the skeptical side, you may want to check out the linked article by Professor Bob Carter:

http://www.aitse.org/global-warming-anthropogenic-or-not/

For an opposing view go to:

http://www.aitse.org/climate-change-anthropogenic-or-not/

Dr Hayhoe’s write-up is a bit short on numbers but it brings up a wide spectrum of arguments advanced by the AGW proponents.

Now, for what it is worth, my personal opinion on the issue of AGW. I accept that the instrumental record, imperfect as it is, appears to show a general warming trend in the global temperatures. I agree that the level of CO2 in the atmosphere is rising, largely as a result of anthropogenic emissions. I have no problem with the physical fundamentals of the greenhouse effect, which assert that the increased levels of CO2 drive climate warming. But this is where my acceptance of the AGW orthodoxy ends. Based mainly on the historical instrumental record I believe that the climate sensitivity to CO2 increase is much lower that assumed in the studies relied on by IPCC. Consequently, I do not consider the warming resulting from the projected increase in CO2 level by 2100 to be dangerous – it may in fact be beneficial. In my opinion the computer models, including the advanced GCM’s, do not contribute much to the debate because they merely process the input data on various feedbacks and this data is of dubious quality. This phenomenon is known in the skeptical circles as GIGO – garbage in, garbage out.

One other argument I am finding very convincing refers to the paleoclimate record – the information on Earth climate in the deep past, long before the instrumental record began. The paleoclimatic data is extracted from ice cores, lake sediments, tree rings and other indirect indicators known as climate proxies.

All_palaeotemps

The above graph shows that the Earth climate went through some wild swings in the pre-historic times. For long periods of time the temperature appears to have been higher than at present. Pleistocene was marked by repeated glacial cycles the cause of which is largely unknown. I also understand that approximately 150 million years ago the level of CO2 in the atmosphere was 5-10 times, and 500 million years ago possibly up to 50 times the current readings of around 380 parts per million.

Phanerozoic_Carbon_Dioxide

This shows that the theory of a stable Earth climate is a myth but the argument which has struck a chord with me goes deeper. The scenario feared by the AGW proponents is that of a runaway warming where an initial warming triggers various positive feedbacks which leads to even more warming and so on. This is, apparently, how Venus became a desert wasteland. But a brief analysis of the paleoclimate records is telling me that if the Earth atmosphere had featured massive positive feedbacks we would have ended up like Venus long time ago. If the levels of CO2 were 5-10 times the current readings for 200 million years in Mesozoic how come the positive feedbacks never kicked in? It is suggested that at one point approx. 250 million years ago up to 3 trillion tons of coal beds burnt off, lit up by volcanism. This event bumped up the global temperature by a few degrees but did not trigger runaway warming.  A number of similar events – far more dramatic than the anthropogenic CO2 emissions – occurred in the pre-historic times and after every single one of them the Earth climate stabilised. This is telling me that the Earth has a built-in thermostat in the form of negative feedbacks.

Among the many angles my climate change series of posts has left unexplored are the politics of AGW, the role of environmental activism, linking  global warming with local pollution, IPCC etc. If you are interested in any of them please let me know through the comments.

THE END

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