Let’s look at two sets of data (a graph and a map) that support the first point in the letter.
The graph “Global Land-Ocean Temperature Index” from 1880 to 2011 is compelling. It clearly shows the long-term, steady increase in global temperatures.
The map titled “Winters are Warming Across the U.S., Trends in Average Winter Temperatures, 1970 – 2012” shows the temperature changes across the lower 48 states. The largest temperature increases are across the northern and northeastern states.
The second point in the letter refers to human activities and the combustion of fossil fuels that releases large amounts of carbon dioxide into the atmosphere.
The third illustration here, “2012 Global Carbon Emissions,” details the amounts of this gas released into the atmosphere in gigatons (billions of metric tons). The 2012 amounts are about 50 percent higher than in 1990 and higher than 2011 as well. Indeed, overall emissions are increasing faster in developing countries such as India and China.
OK, let’s move on to points four and five in the academy letter. Insurance companies follow closely the costs incurred by extreme weather events and the information here is also compelling. The table “Billion-dollar extreme weather events by category, 2011-2012” lists 25 weather events in the United States, by category, costing a billion dollars or more and includes fatalities, economic damages and so on.
These events impacted more than 50 percent of the land mass and a significant percentage of the population of the lower 48 states. The most expensive will be Superstorm Sandy in October 2012, whose costs are now estimated at more than $60 billion.
We must also remember the record-setting floods around Lake Champlain in May 2011, and Tropical Storm Irene, September 2011, which caused tremendous damage to property and infrastructure in Vermont, New York and elsewhere.
Scientists, in a paper published in the Proceedings of the National Academy of Sciences on Feb. 25, 2013, have now identified a physical mechanism behind extreme weather that is tied to climate change.