Day Four: Everything You Need to Know About Global Warming in Thirteen Days

"4) The uncertainties arise when it comes to the interaction between greenhouse gases and other factors in the complicated climate system. It is impossible to be sure exactly how quickly or how much the temperature will rise. But, the past can be measured. The temperature has indeed steadily risen over the past century while greenhouse gas levels have increased. But the forecasts still range very widely for what will happen in the future, ranging from a small but still potentially harmful rise of 1 to 2 degrees Fahrenheit to a potentially disastrous level of +6 to +10 degrees Fahrenheit within this century.

A warmer atmosphere melts glaciers and ice sheets, and causes global sea levels to rise. A warmer atmosphere also contains more energy and holds more water, changing the global occurrences of storms, floods, and other extreme weather events."

Most of the scientists now agree that the low end of the range Mr. Grantham suggests here is unlikely and that the high end is more likely.  The biggest question mark is not the physics and chemistry, though: it's sociology.  So much depends on if we humans can slow emissions enough to stop concentrations at 450 ppm or 560 ppm (double pre-industrial levels) or if we end up with concentrations closer to 1000 ppm.  Right now, the odds of slowing and reversing emissions fast enough or significantly enough seems small.  The human factor, then, is the most important variable that will effect the eventual amount of climate change humans will experience--not the science.  The science, in  fact, keeps getting more and more dire.

[This one of a series of daily posts I am drawing from Jeremy Grantham's Summer 2010 Investment letter.  Mr. Grantham is on the Board of Directors of GMO LLC, a global investment firm with over $100 billion under management.  Mr. Grantham takes a large, worldview perspective on investments--with an eye toward long-term trends.  He is right-on about the impact of global warming.]