Dr. Roy Spencer presents the latest measurements of lower troposphere temperature as measured by two sets of satellites. See his post here. He presents a graph showing measured temperatures versus model predictions.
You can see that actual global temperatures have flattened out since about 1998. The “spaghetti” on the graph represents predictions of 44 models and the black line is the average of model predictions.
Spencer presents three possible explanations for the divergence:
“1) the real climate system is not as sensitive to increasing CO2 as the models are programmed to be.” (His preferred explanation).
“2) the extra surface heating from more CO2 has been diluted more than expected by increased mixing with cooler, deeper ocean waters (Trenberth’s explanation)”
The oceans have a high heat capacity and can absorb great quantities of heat. But have they? The subject is controversial. Anthony Watts discusses the problem here. He notes a recent study which says that between 1955 and 2010, the temperature of the global ocean, between the surface and a depth of 2,000 meters increased in temperature by 0.09 C. That’s not much and Watts wonders if we can even measure to that precision.
“3) increased manmade aerosol pollution is causing a cooling influence, partly mitigating the manmade CO2 warming.”
However, a 2007 satellite-based NASA study shows that aerosols have been decreasing steadily since 1992. In particular, sulfate aerosols have been greatly decreasing since establishment of the 1970 Clean Air Act in the U.S. and similar measures in Europe.
Explanations #2 and #3 seem to have problems. That leaves #1: the climate is not very sensitive to carbon dioxide and is much less sensitive than models assume. The forcing effect of carbon dioxide, if any, is apparently easily overcome by stronger natural forces.
If Spencer’s first explanation is correct, the political war on fossil fuel emissions is futile and will have little or no effect on global temperatures, but that war will cost us dearly by raising energy prices and making our electric grid less reliable.