The chart on the left — from NASA’s Goddard Institute for Space Studies — traces the annual mean global temperature from 1880 to 2008. The line marked “0″ represents the mean for the base years of 1951-80.
That’s pretty compelling evidence of what is happening to the Earth. Some individual years might be cooler than the previous year, just as some individual days each spring are cooler than the previous day, but as in spring, the overall trend is crystal clear.
However, I also want to use that data to make an additional point.
Given the extremely complex nature of climate, it is impossible to “prove” that a specific factor caused a specific climatic effect. Even if the climate changes exactly as the computer models now predict, scientists 100 years from now won’t be able to state beyond a shadow of a doubt that greenhouse gases caused that change. All they will be able to say with scientific honesty and certainty is that the change was consistent with greenhouse theory.
In other words, if you’re waiting for absolute proof of global warming, it will never come. And that’s the opening that the deniers and pooh-poohers try to manipulate.
But I want to point you to the late ’70s on the chart. That’s about the time that leading scientists began to warn pretty consistently that climate change was a danger. They didn’t know for absolute certain what was going to happen. But they thought they had a pretty good idea, and they said so in public.
And indeed, look what happened. Over the next 25-30 years, the climate behaved just as they predicted it would. Global temperatures began to rise, and as the Goddard folks point out, “the ten warmest years all occur within the 12-year period 1997-2008.”
Personally, I think that buys the experts a lot of credibility. If I’m watching a baseball game and the guy in the next seat says “He’s gonna hit to shortstop,” and then the player hits it to shortstop, I’m intrigued. If he gets it right batter after batter, I’m really impressed. And that’s pretty much what climate scientists have achieved.
The chart on the right, by the way, shows those portions of the Earth that were warmer (red) or cooler (blue) than normal in 2008, which was the ninth warmest of the last 128 years.