Dr. Pierrehumbert is the Louis Block Professor in Geophysical Sciences at the University of Chicago. He was a lead author of the IPCC Third Assessment Report, and a co-author of the National Research Council study on abrupt climate change
The following quote is from Principles of Planetary Climate by Raymond T. Pierrehumbert ( http://geosci.uchicago.edu/~rtp1/ ). This is a scientific proof, just take your time reading it.
“In the year 2005, over 8 gigatonnes (8·10^12kg) of carbon were released by fossil fuel burning, and annual emissions continue to grow rapidly.
There are several ways to see that this is a very big number – a major upset to the natural carbon cycle:
First, the pre-industrial atmosphere contained about 600 gigatonnes of carbon, so the 2005 annual emission is fully 1.3% of the undisturbed atmospheric content. If the same amount were released into the atmosphere each year, it would take only 75 years to double the atmospheric CO2 content, provided all the released CO2 stayed in the atmosphere.
Alternately, one could compare the fossil fuel emissions to the volcanic outgassing which in the long term balances silicate weathering and sustains the carbon cycle. Precise estimates of volcanic outgassing are hard to come by, but generally are on the order of 0.1 gigatonnes of carbon per year or less. Thus, fossil fuel carbon emissions are eighty times larger than background volcanic outgassing.In fact, the very largest carbon flux number involved in the whole carbon cycle is the net CO2 carbon fixed into organic carbon each year by worldwide photosynthesis, and fossil fuel emissions even look impressive when compared to this number.
Based on satellite chlorophyll observations, it has been estimated that photosynthesis fixes 100gigatonnes of carbon each year, about half on land and half in the oceans. The year 2005 fossil fuel emissions were fully 8% of this number. In other words, worldwide photosynthetic productivity would have to increase by 8% to take up the fossil fuel CO2 and 100% of that carbon would have to be buried as organic matter without being recycled by respiration. That, of course, would be a completely absurd situation, as virtually all of the photosynthetically fixed carbon is quickly respired back into the atmosphere, largely by bacteria who have had several billion years to become proficient at making use of organic carbon wherever they find it. As an example, land photosynthesis fixes about 50 gigatonnes of carbon each year, but the flux of organic carbon to the oceans in all the world’s rivers is a mere 0.4 gigatonnes per year (one twentieth of fossil fuel carbon emissions). And there is no evidence that much of the remainder of the photosynthetically fixed carbon is remaining on land as soil organic carbon.
To say that humans have become a force of geological proportions vastly understates the case, for by this measure human influences on the carbon cycle overwhelmingly dominate the natural sources.”
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