Via John Whitehead, I was led to this discussion of climate change by the EPA. The EPA repeats the following claim from the IPCC:
The average surface temperature of the Earth is likely to increase by 2 to 11.5°F (1.1-6.4°C) by the end of the 21st century, relative to 1980-1990, with a best estimate of 3.2 to 7.2°F (1.8-4.0°C) (see Figure 1). The average rate of warming over each inhabited continent is very likely to be at least twice as large as that experienced during the 20th century.
Does the standard error on this century-long forecast seem small to anyone else? (I’m not being facetious, I’m genuinely asking in the hopes that those will greater knowledge of the issue will answer.)
The Everyday Economist 
IPCC says that the 20th century temperature rise was 0.7 degrees C. That included a large rise 1900-1930 followed by 40 years of falling global temperatures between 1940-1970. The range of their projection is 1.1 to 6.4 degrees. All of this is based on climate models that have (so far) greatly exaggerated the 1990-2010 temp. rise. So we have unverified models being used to generate projections 100-years out. I think the true error bars are vast.
Also, the geologic name for now is an “inter-glacial” period. The last million years have seen eight or nine periods of glaciation (about 80000 years long) followed by 10-20000 years of warming. We are near the end of one of those short warm periods. The most likely future for Earth is cold, not warm!