The Hockey Stick
One of the most compelling pieces of evidence for human influence in climate change is a famous chart showing variations in temperature over the last 1000 years. In this graph, the variation in temperatures over the last century clearly breaks out of the long-term pattern, resulting in the so-called "hockey stick" shape. That breakout coincides with the dramatic increases in fossil fuel use in the Industrial Era. So A+B = clear evidence of anthropogenic climate change. But it now appears that the analytical technique used to create the 1000 year temperature chart in question may have been flawed. If so, while not exactly destroying the notion of global warming, it would force us to rethink the distinction between natural and man-made warming.
If you've been following my blog for a while, you know I take climate change very seriously. My nose is attuned to the smell of anti-climate change propaganda, but this article from MIT's Technology Review doesn't come across that way. Rather, this is how science--and the scientific method--works. Someone analyzes a bunch of data, reaches a conclusion, and then others try to replicate that result and discover any flaws in the methodology. That process seems to be well represented here, with peer-reviewed articles, responses by the original researcher, and so on. It could take years to play out.
We know that there have been warming and cooling trends in the past, both from historical records and from the observable evidence of the geological past. The key question is where the current warming trend (which is real) fits in the context of previous ones. The hockey stick graph suggests it is unprecedented, but if that turns out to be invalid, then we must at least reconsider the relationship between human drivers of warming and natural ones. That could have profound implications for climate change policy, perhaps even pushing us toward an adaptation strategy and away from emissions management. Stay tuned.