The most recent drafts of the IPCC’s Assessment Report and Summary for Policy Makers are going through final review before release near the end of September. These drafts have been leaked and the final versions, which very well could be different than the drafts, will be as controversial as the Fourth Assessment Report. The debate over how much humans contribute to warming remains unresolved, although assertions that most of the warming is due to human activities is getting harder to defend.
According to some sources, IPCC scientists will assert that they are convinced more than ever that global warming is caused by humans. By itself this is a meaningless statement because no one or very few argue that humans do not contribute to global warning. The debate is about how much.
The IPCC will assert that it is 95% certain that our use of fossil fuels is the main reason behind the global rise in temperatures since the 1950s. In the previous report, it claimed to be 90% certain. The use of probability estimates is misleading in that they are estimates based on opinion, not empirical evidence and quantitative analysis.
The recent slowing of the temperature trend is currently a key issue, yet it has not been adequately addressed in the SPM, according to an official paper that includes all governmental comments on the draft report. The U.S. has requested that information on recent hiatus in global mean air temperature trend be added.
According to reports, the IPCC will attribute it to natural meteorological variations and other factors that could include greater absorption of heat into the deep oceans – and the possibility that the climate is less sensitive to carbon dioxide than had previously been believed.
Attempting to adequately address the recent trend is important because so called “skeptics” of man’s influence on warming use the slowing pace of temperature increase as evidence that IPCC scientists have exaggerated the impact of manmade greenhouse gases. The slowing supports the view that there’s less need for expensive carbon suppressing policies.
The draft SPM notes that the rate of warming over the past 15 years “is smaller than the trend since 1951”, citing a rate of about 0.05 degrees C per decade in the years 1998 through 2012 compared to a rate was about 0.12 degrees per decade from 1951 through 2012.
The IPCC will claim that 15-years of observation is not sufficient to give a qualified analysis of the global surface temperature trend in an assessment of climate change. Germany said. It also said the use of the word “hiatus” is “strongly misleading” because “there is not a pause or interruption, but a decrease in the warming trend.” It is ironic that 15 years of essentially no warming is inconclusive when a similar period was used in the late 80s as definitive evidence of runaway warming. Dr. Roy Spencer has conducted research that suggests that the Pacifical Decadal Oscillation cycle has had a major influence in the warming from the mid-70s and the cooling since 1998.
Some scientists have suggested that the slowdown means that climate sensitivity is lower than assumed by the IPCC. The draft report includes possible reasons for the slowing rate, including natural variability, volcanic eruptions and a drop in solar energy reaching the Earth. But, these reasons are not one-time events, they occur regularly and are consistent with a lower sensitivity.
One thing seems certain. The IPCC will not admit to past errors in its assessments or to the inadequacy of the models on which it has relied on to support its preconceived judgments. Hence, there will be a lot of spin and the debate will continue.
This article appeared on the FuelFix weblog at http://fuelfix.com/blog/2013/09/04/the-next-ipcc-report-leaks-spin-and-efforts-not-be-embarrassed/