This morning Google Now featured excitable stories “Bipartisan Panel of Scientists Confirms Humans are NOT Responsible for Past 20,000 Years of Global Warming.”
Indeed the brave iconoclast Mo Brooks (Alabama 5th District) on July 11th got Dr. Twila A. Moon to say “So, I would agree that when it began 20,000 years ago when we were coming out of the last glacial that was not caused by humans. The warming of the last 100 years, most certainly was.” Still, the latest denialist tack has a certain nihilistic appeal: if warming happens whether we’re around or not, what’s the big deal? Earth is just warming up out of an ice age, nothing to see here.
But what nobody seems to have noticed is the howler is in Mo Brooks’ framing remarks. Quoting from his own press release:
By way of background, during the last glacial maximum of roughly 20,000 years ago:
- Average global temperatures were roughly 11 degrees Fahrenheit COLDER than they are today (per Zurich University of Applied Science). Stated differently, global temperatures have risen, on average, roughly 0.5 degrees Fahrenheit per century over the past 20,000 years.
See the problem? 10°F ÷ 20,000 = 0.0005°F per year = 0.05°F per century. He’s wrong by a factor of 10 about the warming per century! Stated another way, if temperatures had risen 0.5°F per century for 20,000 years as he claims, it would be roughly 100°F warmer now.
Please, if you know a journalist, help me expose this math-illiterate idiocy. This garbage is being promoted by Rush Limbaugh and a bunch of right-wing sites, it needs the same ridicule that Mo Brooks got last year for suggesting rocks falling into the sea are causing sea levels to rise.
Yes it’s warmed since the ice age. But the recent warming is of a different magnitude. NASA’s Earth Observatory summarizes it (emphasis mine)
As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming.
Models predict that Earth will warm between 2 and 6 degrees Celsius in the next century. When global warming has happened at various times in the past two million years, it has taken the planet about 5,000 years to warm 5 degrees. The predicted rate of warming for the next century is at least 20 times faster. This rate of change is extremely unusual.
Finding a good graph
Alas that web site doesn’t have a graph of temperature over the last 20,000 years. If you zoom out too much the recent warming doesn’t show up: if you zoom in you can’t see the slow warming over millennia then a century of rapid warming on the same graph. The best medium-term graph I’ve seen is from the XKCD online comic #1732 (as the meme goes “Obligatory XCD: https://xkcd.com/1732/.” I’ll end this by including it in full (I’m allowed to, it’s under a Creative Commons Attribution-NonCommercial 2.5 License).