If man-made greenhouse gas emissions are going to cause more droughts and storm surges on a persistent basis, why did it take so long? And why is it only a concern in the last 25 years, rather than in the 1930s, when things were really hot?
A new estimate claims it's because the natural atmosphere already contained carbon dioxide that human-induced changes were relatively small. Had these natural concentrations been lower, the effects of the emission of harmful greenhouse gases would have been felt much earlier.
Writing in Climatic Change, David Archer of the University of Chicago notes that The concentration of carbon dioxide molecules in the atmosphere is measured as parts per million of dry air, or ppm. In the recent climatic past and earlier glacial periods, this level fluctuated between 180 ppm and 260 ppm while in the more distant past is was far higher. But measurements taken of Antarctic sheet ice show that the concentration of naturally occurring carbon dioxide in the atmosphere was already 278 ppm in the 1750s, before the Industrial Revolution.
Had that concentration been half what it really was, which isn't really possible - we'd be dead with so little CO2 - the climate change that estimates are projecting for 2050 would have already been here. And if the CO2 were only 10 percent of what it was, climate change would have happened by 1900, except there would have been no Industrial Revolution because we'd be dead and whatever species dominated were unlikely to produce CO2.
So Archer believes climate change is only moderate because of so much natural CO2. It's a kind of ecological harmony mythology for the atmosphere. And society would not have been mature enough to deal with it had it occurred sooner.