Letters to the Editor
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Clarifications on global warming
(1) Al Gore is right that there is scientific unanimity on anthropogenic global warming if you take peer-reviewed publications as the relevant figure of merit.
(2) The ice core data from Greenland and Antarctica provide the crucial differentiation between naturally occurring climate cycles and the effects of humans in the most recent 200 years. The data
http://www.sciencemag.org/cgi/content/full/283/5408/1712
show that carbon dioxide and methane increases lag temperature increases by 600-1000 years in each of the natural cycles, whereas in the last 200 years, the carbon dioxide has increased to levels unprecedented for the past half-million years, and temperature increases have followed; the CO2 leads temperature now. This is easy to understand: in the long natural cooling cycles, carbon is stored in peat underground and in methane hydrates underwater. When temperatures rise due to earth orbital orientation changes, these reserves of carbon decompose, release gas, and boost the heat retention, resulting in even higher temperatures - a classic positive feedback loop. And it's the temperature that drives the system, so it has the phase lead. Now, in the past 200 years, we humans have removed very deep deposits of carbon - oil and coal - and burned them, boosting the greenhouse gas load beyond anything in the history contained in the ice core data. And we have measured the recent temperature changes, with increasing accuracy as time goes on, and the mean temperature is rising, following the CO2 and methane. This phase relationship is the smoking gun.