I wrote today about global warming stalling out the last 15 years or so (the hook was this Economist piece Wesley mentioned in here the other day), and how it hasn’t yet made an impression on the “deniers,” i.e. all those advocates of limits on carbon emissions who are so certain of the science that they have no interest in the latest evidence. Now, the warming trend could start again at any time, but the current cessation suggest how little we really know about the global climate.
As for the science being “settled,” consider James Hansen. In 2009, he warned of new coal-fired plants in the most apocalyptic terms (emphasis added in all quotes):
Over a year ago I wrote to Prime Minister Brown asking him to place a moratorium on new coal-fired power plants in Britain. I have asked the same of Angela Merkel, Barack Obama, Kevin Rudd and other world leaders. The reason is this — coal is the single greatest threat to civilization and all life on our planet…
The trains carrying coal to power plants are death trains. Coal-fired power plants are factories of death. When I testified against the proposed Kingsnorth power plant, I estimated that in its lifetime it would be responsible for extermination of about 400 species — its proportionate contribution to the number that would be committed to extinction if carbon dioxide rose another 100 ppm. Of course, we cannot say which specific species should be blamed on Kingsnorth, but who are we to say that any species are worthless?
Now, just four years later, he is arguing that all the new coal-fired plants have saved the planet from more global warming, by “fertilizing” the biosphere and creating aerosols that are a global coolant (these quotes are from the synopsis in the Huffington Post):
We suggest that the surge of fossil fuel use, mainly coal, since 2000 is a basic cause of the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks. One mechanism by which fossil fuel emissions increase carbon uptake is by fertilizing the biosphere via provision of nutrients essential for tissue building, especially nitrogen, which plays a critical role in controlling net primary productivity and is limited in many ecosystems…
Independent of a possible aerosol effect on the carbon cycle, it is known that aerosols are an important climate forcing. IPCC17 concludes that aerosols are a negative (cooling) forcing, probably between -0.5 and -2.5 W/m2. Hansen et al., based mainly on analysis of Earth’s energy imbalance, derive an aerosol forcing -1.6 ± 0.3 W/m2, consistent with an analysis of Murphy et al. that suggests an aerosol forcing about -1.5 W/m2. This large negative aerosol forcing reduces the net climate forcing of the past century by about half.
The threat now is that we will eventually stop building coal-fired plants, and thus unloose all the suppressed warming. From the paper itself:
Reduction of the net human-made climate forcing by aerosols has been described as a ‘Faustian bargain’ (Hansen and Lacis 1990, Hansen 2009), because the aerosols constitute deleterious particulate air pollution. Reduction of the net climate forcing by half will continue only if we allow air pollution to built up to greater and greater amounts. More likely, humanity will demand and achieve a reduction of particulate air pollution, whereupon, because the CO2 from fossil fuel burning remains in the surface climate system for millennia, the ‘devil’s payment’ will be extracted from humanity via increased global warming.
Now, for all I know, the latest Hansen view is correct. But it doesn’t seem very settled. His paper includes this passage lamenting all that we don’t know about the effect of aerosols on the climate:
Natural forcings, by changing solar irradiance and volcanic aerosols, are well-measured since the late 1970s and included in most IPCC (2007) climate simulations. The difficulty is human-made aerosols. Aerosols are readily detected in satellite observations, but determination of their climate forcing requires accurate knowledge of changes in aerosol amount, size distribution, absorption and vertical distribution on a global basis–as well as simultaneous data on changes in cloud properties to allow inference of the indirect aerosol forcing via induced cloud changes. Unfortunately, the first satellite mission capable of measuring the needed aerosol characteristics (Aerosol Polarimetry Sensor on the Glory satellite, (Mischenko et al 2007)) suffered a launch failure and as yet there are no concrete plans for a replacement mission.
Over at Powerline, Steve Hayward had a good post on the big-picture implications of the absence of new warming.