“Climate change is occurring, is very likely caused by human activities, and poses significant risks for a broad range of human and natural systems.”
That’s what the National Academy of Sciences concludes in a report recently released by its study arm, the National Research Council. Not surprisingly, the ever careful academy notes that science can’t yet nail down exactly how or when the impacts of climate change on humans and the environment will play out. But despite these uncertainties, the academy concludes that “the environmental, economic, and humanitarian risks of climate change indicate a pressing need for substantial action to limit the magnitude of climate change and to prepare to adapt to its impacts.”
To have the academy find a “pressing need” for action in the midst of scientific uncertainty is big news, especially for those who want to defer action on climate change. Typically, the proponents of delay argue that prudent policy should wait for science to be absolutely sure before acting. Yet the academy’s position is clear: even though we still have more to learn, in the case of climate change we know enough to begin acting now.
In arriving at this position, the academy study committee (full disclosure – I was a member) considered rough estimates of how much time the world has before the rise in global average temperature (relative to pre-industrial times) hits 2 degrees Celsius, the limit agreed to by world leaders in the Copenhagen Accord. This so-called “emissions headroom” depends on two things: 1) the rate of global greenhouse gas emissions, and 2) how sensitive the climate system is to the atmospheric concentration of greenhouse gases. Scientists have narrowed the potential climate sensitivity to a reasonable range, but some uncertainty still exists. If the climate is very sensitive, then our emissions headroom could be only about 40 years. (It could be even less if global emissions continue to increase, as they are expected to.) On the other hand, if the climate is not very sensitive and global emissions remain relatively flat we could have more than 100 years before global average temperatures rise by 2 degrees Celsius. Given this substantial range, sensible cases can be made for either for prompt action or a more relaxed response. But in the judgment of the academy committee, prompt action is warranted because the risks of delay substantially outweigh the risks of acting too soon.
To see why this is so, suppose policy makers elect to delay action, hoping that they have a century or so to solve the climate problem. If the climate system turns out to be very sensitive and global greenhouse emissions continue to grow, we would have only a couple of decades to reduce global greenhouse gas emissions to nearly zero to avoid a temperature increase higher than 2 degrees Celsius. That would require a massive transformation of global energy production and use in a very short time. That’s expensive. In addition, if we cannot reengineer our energy system quickly enough, we will have to take drastic steps to successfully adapt to the resulting climate change-related impacts. That’s also expensive.
Now consider what happens if policy makers decide to act promptly to reduce greenhouse gas emissions and take steps to adapt to some amount of climate change, but the climate system isn’t very sensitive and changes slowly. In this case, we would have spent money limiting emissions and adapting sooner than was necessary. Compared to the cost of the crash efforts described above, this cost is likely to be modest. Moreover, if it’s determined that climate sensitivity is low, then throttling back policies that limit future climate change would be relatively easy. Meanwhile, we’d get the substantial ancillary benefits of modernizing our energy infrastructure. All in all, this is a much more manageable situation than the one created by being wrong in the other direction.
While the academy’s analysis is specific to the climate change issue, the trade-off it addresses is in fact a common situation for policy makers. Consider, for example, the recent flooding of the Mississippi River system. Local, state and federal officials all characterized their management strategy in exactly the same way: hope for the best, but prepare for the worst. That’s very much the stance that the academy has taken on climate change and one that should motivate policy makers to begin to act now with confidence.
A final personal note. In Washington policy debates it’s all too common to hear that action should wait for a final answer from science. That is almost always an excuse not to act on a serious problem. Science constantly has new questions to address, and so getting its final answer results in a very long wait. But, as in the case with climate, science often knows enough to sound the alarm even before it can tell policy makers exactly what to do. Policy makers need to deal with the real, if not completely understood risks, not hide behind scientific uncertainty as a reason for doing nothing.