Old ice reveals information about atmospheric conditions that prevailed when it was formed, and it shows rises in atmospheric carbon-dioxide levels lagging rises in global temperatures. That is, historically, the earth’s temperatures went up first, then CO2 concentrations followed.
For some, this is evidence that the idea of human-induced climate change is a fraud, and their case is strengthened by the fact that the graph everyone remembers from An Inconvenient Truth is the one where Al Gore uses a mechanical lift to show what’s happened to CO2 concentrations since the industrial age began.
Some skeptics use this fact — and it is a fact — to dismiss the whole idea of atmospheric global warming. The syllogism goes like this:
- Climate-change fearmongers say atmospheric carbon dioxide contributes to climate change
- Things other than human influence have previously increased the level of carbon dioxide in the atmosphere
- Therefore, the science of climate change is bunk.
Blogger “Reasic” has a learned post today explaining why this argument is nonsensical not just on logical principles, but citing specific facts. Scientists haven’t just looked a little cross-eyed at what happened in the past, seen what’s happening now, and sounded the alarm.
The Milankovitch Cycles [changes in the earth’s orbit and physical attitude toward the sun] are known to be the catalyst for sending our planet into and out of ice ages. These cycles are also considered to be too weak to cause the entire amount of warming that occurs between glacial and interglacial periods. It is understood that, once warming starts around Antarctica and CO2 is released, a positive feedback is started – as temperature increases, CO2 increases, which increases temperature again, etc. This continues in increasingly smaller increments until equilibrium is reached.
Nobody respectable is seriously arguing that climate change is due entirely to human activity — of course there are natural cycles and we’re in one now. The concern is that we’ll exaggerate the natural effect by emitting extra gases into the atmosphere, possibly irreversibly (at least until the next ice age comes upon us, which is a matter of millennia, not decades).