This website is no longer actively maintained
Some material and features may be unavailable
Robert FriBack to OpinionRobert Fri

The climate dilemma: How warm and when?

Last summer, the National Research Council concluded that “a strong, credible body of scientific evidence shows that climate change is occurring, is caused largely by human activities, and poses significant risks for a broad range of human and natural systems.” As if to dramatize this conclusion, the National Climatic Data Service recently reported that 2010 tied 2005 as the warmest year on record since 1880. So why aren’t our national leaders rushing to tackle the climate problem?

Boatmen wait for commuters to cross flood waters outside of Dhaka, Bangladesh, in 2007. Many scientists attribute increased flooding in the country to global warming. Photo: AP/Pavel Rahman

Politics plays a big role in explaining why the nation lacks a coherent climate policy, of course. But even for those who agree that the National Research Council is right, and I think it is, crafting sensible climate policy is hard. Here’s the problem: Climate science makes a strong case for taking action, but it can’t yet tell policy makers exactly what to do. As a result, policy makers have to strike a balance between what we know and what we’re still learning about. It’s the policy makers’ dilemma.

Since the science isn’t fully settled, it’s really important that policy makers and the public understand where climate science actually stands. Otherwise, the policy debate gets taken over by extreme claims – on both sides – about what advocates would like the science to say. I’m not a scientist but having listened to many of them while participating in the National Research Council climate project, I found that parsing the science message into three parts helps non-scientists to grasp the essentials.

First, the greenhouse effect is real. There’s simply no doubt that the Earth retains some of the energy provided by solar radiation. The Sun’s rays hit the Earth and, as they are reflected back, the atmosphere absorbs some of the energy. If the greenhouse effect did not exist, the planet would be a lot colder. This is settled science.

Second, adding greenhouse gases to the atmosphere will warm the planet, but when and by how much isn’t nailed down. Almost all scientists agree that adding greenhouse gases like carbon dioxide to the atmosphere has raised the temperature of the planet over the past century. And they agree that pumping out more greenhouse gases will up the temperature still more — but by how much is still a matter of debate. The uncertainty arises because the climate system is very complex and it’s hard to predict its behavior. For example, warming the atmosphere will change how clouds form in ways that could either restrain or amplify a change in temperature, but it’s not yet entirely clear how to predict cloud formation with great precision.

The uncertainty about how much temperatures will change in response to greenhouse gas emissions accounts for a fair amount of the controversy surrounding climate change. Depending on what one assumes about the sensitivity of the climate to increased greenhouse gases, the range of temperature response is pretty broad. If climate sensitivity is low, the temperature increase is less of a problem; at least we have until late in this century before the effects of climate change become serious. But if climate sensitivity is at the high end of the range, it’s already too late; we’ve added enough greenhouse gases to the atmosphere to blow through the tolerable warming level in only a few years.

Third, predicting the real world impact of global warming is very hard. The outcomes of changes in the Earth’s temperature are what really concern policy makers. How much will the seas rise and how fast? Which regions will get drier and which will get wetter? And famously, how fast will the glaciers melt? Unfortunately, science isn’t yet very good at making these predictions. Doing so involves too many assumptions about the behavior of complex human and natural systems to predict much more than broad trends over large areas.

Life would be much simpler if policy makers knew exactly how to respond – exactly what the temperature increase will be, how long they have before it gets too high, and what problems it will create for important human and natural systems. Absent these answers, policy makers have to hedge against doing either too much or too little.

Bringing clarity to policy is the reason that an aggressive climate research program to resolve the scientific uncertainties is so essential. In the meantime, however, what we do know makes a compelling case for acting on the climate problem.

Robert Fri is a visiting scholar at Resources for the Future, a nonprofit organization that studies natural resource and environmental issues. He has served as director of the National Museum of Natural History, president of Resources for the Future, and deputy administrator of both the Environmental Protection Agency and the Energy Research and Development Administration. Read his full bio.