Re: [asa] climate change severity

At 12:42 PM 1/4/2007, Charles Carrigan wrote:
>Don,
>
>Human beings began pumping CO2 into the atmosphere well before
>1930. I understand wanting to be skeptical of bandwagons, but the
>data that indicate human impact are pretty strong. Natural warming
>may also be occurring, but the data clearly show a massive
>anthropogenic involvement.
>
>Ice core measurements indicate that in the year ~1800, the
>concentration of CO2 in the atmosphere was down near 275 ppm, but
>steadily rising over the next 100 years to reach ~300 ppm by
>1900. Direct measurement of atomospheric CO2 goes back to the late
>1950s, when the value was up to ~315 ppm; today it is near ~375
>ppm. Although we've certainly done much more in the past 50 years,
>humans did plenty between 1800 and 1930.
>
>To put it in natural context - in the deep geologic record, CO2 has
>fluctuated in the atmosphere between ~180-280 ppm over the last at
>least 400,000 years, and I believe the record now goes back even
>further to the past 650 ka; at no point in that history has CO2
>reached the levels it is at today, or even the levels it was at in
>1950. The concentration of CO2 in past atmospheres is measured by
>trapped gas bubbles in deep ice cores from Antarctica. There is a
>tremendous inverse correlation between times of low CO2 (~180 ppm)
>and large amounts of continental ice as interpreted by delta18O data
>(stable isotopes of H2O), and also the reverse - times of high CO2
>(~280 ppm) correlate with times of low continental ice. This
>obviously fits with the notion that CO2 is a greenhouse gas.
>
>A couple of references:
>Petit, J.R., et al., 1999, Climate and Atmospheric History of the
>Past 420,000 Years from the Vostok Ice Core, Antarctica. Nature,
>399, 429-436.
>Friedli et al., 1986, Ice Core Record of the 13C/12C Ratio of
>Atmospheric CO2 in the Past Two Centuries. Nature, 324, 237-238
>
>There is no question that human beings over the past 200 years have
>dramatically altered the concentration of CO2 in Earth's
>atmosphere. There is also a clear connection between CO2
>concentration and global T.
>
>Best,
>Charles

@ I see you didn't get the
memo. http://cagle.msnbc.com/working/061213/lester.jpg

~ Janice

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Received on Thu Jan 4 12:48:44 2007