During the past week I have gotten several emails from folks who said they had absolute proof that human-induced global warming is nonsense.

The argument they offer:  volcanoes put out way more CO2 than human activities. So it doesn’t matter what we do!

Since I have heard this claim at least a dozen times during the past few months, I thought I should just give the facts:  HUMANS EJECT WAY MORE CO2 INTO THE ATMOSPHERE EVEN DURING MAJOR VOLCANO YEARS.

A number of studies have shown that global volcanic activity injects about 0.15 to 0.26 gigatons per year of CO2.  Anthropogenic CO2 emissions produced by mankind provide about 35 gigatons of CO2 in 2010.   Way more.

To put it another way:  current volcanic activity puts out about as much annually as our states of Florida, Michigan, and Ohio.  We have a lot more states and then there is the rest of the world!

The following figure (from a very nice article in EOS by Terry Gerlach of the Cascades Volcanic Observatory in Vancouver, 14 June 2011, volume 92, No. 24, pg 201-202): shows the ratio (the ACM) between human and volcanic CO2 emissions (shown by the dots).  The range of uncertainty (based on the uncertainty in volcanic emissions) is show by the brackets.  What one should conclude is that  human emissions dwarf volcanoes and the ratio is increasing.  Today we put out well OVER A HUNDRED TIMES more than volcanoes.