Over the weekend, a Norwegian climate change study from last year got a fair amount of attention online, thanks to what appears to be a new English translation of a press release from October. The work incorporates data from the last several years, during which global temperatures remained fairly steady. It suggested that the climate may not be as sensitive to carbon dioxide levels in the atmosphere as previously thought. If carbon emissions double from pre-industrial levels, the world might warm by 1.9 ° C, which is on the low end of a range of estimates from the Intergovernmental Panel on Climate Change.

The good news is tempered by the fact that greenhouse gas emissions are increasing, which means greenhouse gas levels could more than double, even if the world acts to quickly reduce emissions (see “Solving Global Warming Will Require Far Greater Cuts than Previously Thought”).

It’s also tempered by the fact that this study, like all climate change studies, aren’t certain, but are estimates. It’s difficult to for climate scientists to predict how greenhouse gases will affect the climate because the climate system is so complex. Scientists are still learning how clouds will respond. The role of emissions other than carbon dioxide is also unclear. For example, a recent study suggested that black soot could have a bigger impact on climate than thought. The study in Norway itself doesn’t actually give one figure for warming, but a range of possibilities—including possible warming levels higher and lower than 1.9 ° C, because of the uncertainty involved.

Add to this uncertainty the uncertainty of what even 2 ° C would do to the weather and the uncertainty about how much it will cost to wean the world from fossil fuels.  

This all makes establishing sound policy difficult, to say the least. Scientists have a high degree of confidence that anthropogenic greenhouse gases are responsible for a large share of the roughly 1 ° C rise in temperatures we’ve seen so far, and that it will lead to warming in the future. Since no one can say precisely how much, and that’s why it’s so important to have a high level, prominent discussion in the United States and around the world about the risks of climate change, and how best to respond (see “Obama Still Needs to Make the Case for Dealing with Climate Change”).