Can we zero in on Earth’s sensitivity to CO₂?

Enlarge (credit: Kristin Andrus)

If it were easy to pin down the exact value for our planet’s sensitivity to greenhouse gas emission, it would have been done a long time ago—and you wouldn’t be reading yet another news story about it. It's not like we have no idea how sensitive the climate is. The range of possible values that scientists have been able to narrow it down to only spans from “climate change is very bad news” to “climate change is extremely bad news.”

But the difference between “very bad” and “extremely bad” is pretty important, so climate scientists aren’t throwing up their hands anytime soon—as two new studies published week show.

There are several basic strategies available for calculating the climate's sensitivity. These range from studying climate changes in the distant past to building and evaluating climate models to analyzing the warming over the last century or so. Each has pros and cons. A handful of studies looking at the last century made waves a few years ago for yielding oddly lowball estimates of the impact of CO₂ on warming, for example. Later studies have found problems that push those estimates upward when corrected, but one of this week’s studies demonstrates that the entire strategy is inherently problematic.