Several estimates of aggregate net economic costs of projected damages from climate change across the globe are now available. These are often expressed in terms of the social cost of carbon (SCC), the aggregate of future net benefits and costs, due to global warming from carbon dioxide emissions that are discounted to the present. Peer-reviewed estimates of the SCC for 2005 have an average value of US$43 per tonne of carbon (tC) (i.e., US$12 per tonne of carbon dioxide, tCO2) but the range around this mean is large. For example, in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon (US$-3 per tonne of carbon dioxide) up to US$350/tC (US$95 per tonne of carbon dioxide.) In a 2004 remark on the economic effect of global warming in Copenhagen Consensus, Professor Robert O. Mendelsohn of Yale School of Forestry and Environmental Studies, stated that.
A series of studies on the impacts of climate change have analytically shown that the older literature overestimated climate damages by failing to allow for adaptation and for climate benefits. Countries in the polar region are likely to receive large benefits from warming, countries in the mid-latitudes will at first profit and only begin to be debilitated if temperatures rise above 2.5C. Only countries in the hot and subtropical regions are probable to be harmed right away by warming and be subject to the magnitudes of impacts first thought likely. Summing these regional impacts across the globe implies that warming benefits and damages will likely offset each other until warming passes 2.5C and even then it will be far smaller on net than originally thought (Mendelsohn and Williams 2004).” McKibbin and Wilcoxen (2002) cite the United Nations IPCC as concluding with 33 to 67 percent self-belief that the aggregate market sector effect of a small increase in global temperatures could be “plus or minus a few percent of world GDP”. Developed countries are more likely to experience positive effects and developing countries are more likely to experience negative effects. Larger temperature increase would be more adverse across the board. McKibbin and Wilcoxen do not endorse GDP as a welfare measure.