Dr. James Hansen is publishing a paper next week that warns of future warming at a much faster pace than the official IPCC forecasts. He has summarized his scientific paper In multiple recent communications, explaining the differences between his forecasts and those of the Intergovernmental Panel on Climate Change, IPCC. The recent spike in global temperatures, coupled with rapidly declining reflected solar radiation and Antarctic sea ice extent support Hansen’s views.
The IPCC has based its forecasts of warming solely on climate models. Dr. Hansen has taken a three pronged approach of forecasting using models, climate history going back into the geologic past, and ongoing observations. Because many of the changes observed in the geologic record were slow, IPCC scientists have not included those slow processes in their models. Scientists will continue to debate how to use paleoclimatology to improve models and predictions. What is clear from paleoclimatology is that sudden changes happen and our climate models may not be able to forecast those sudden changes.
Recent observations support Hansen’s warning that the earth is heating up at a rate well above IPPC forecasts. Hansen hypothesized for the past decade that IPCC models underestimated the sensitivity of the climate to greenhouse gases because they underestimated the cooling effects of pollution. In particular, sulfurous gasses produced by burning fossil fuels act as a powerful reflector when they interact with water. Atmospheric sulfur pollution bonds with water to form tiny droplets, smaller and more reflective than normal cloud droplets. These clouds are powerful at cooling the climate.
The clouds that have the most impact at cooling the climate are polluted low stratus clouds, the type of clouds that frequent the west coasts of California and Africa, plus the northern Indian ocean in the cool season. These waters, and the vast trade wind belts in the eastern Atlantic and eastern Pacific that stratus clouds cool are also global shipping routes. The reason that these clouds are so effective at cooling is that at night they radiate out heat just a little less than the ocean below would, while they reflect back far more solar energy during the day than the ocean would. Over the past decade, sulfur pollution limits have been imposed on shipping, greatly reducing sulfur aerosols over the northern hemisphere’s region where stratus clouds proliferate. One indication that Hansen’s warning about IPCC models underestimating the cooling effects of sulfur pollution would be a sudden recent heating over the stratus belts of the north Pacific and north Atlantic. That’s exactly what his figure 7 above shows. There has been a rapid increase of solar energy uptake of the north Pacific and north Atlantic.
And in the southern hemisphere where there’s far less pollution an increase in the welling up of relatively warm intermediate water in the southern ocean has led to a collapse in the sea ice extent around Antarctica. The loss of reflective sea ice means that the ocean is taking up more solar energy there and that the formation of the earth’s coldest deep water is in rapid decline. Dr. Hansen has been warning us of the developing decline of this ocean circulation for over a decade.
James Hansen's latest letter is here.
Global Warming in the Pipeline will be published in Oxford Open Climate Change of Oxford University Press next week.
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