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The Bottom Line on Climate Is in the Air

Dan Lashof

Posted March 7, 2013

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If you want to know the bottom line on how the effort to curtail dangerous climate change is going, check what’s happening to the atmosphere’s concentration of heat-trapping carbon dioxide (CO2). That’s just what the National Oceanic and Atmospheric Administration (NOAA) does, and this week they released scary new data showing that things aren’t going very well:  Last year, the concentration of carbon dioxide in the atmosphere jumped by 2.6 parts per million (ppm), to a forbidding 395.1 ppm as of January, 2013.

That’s a 10 ppm rise over the last five years and more than a 40 percent increase since humans started transforming massive quantities of fossil fuel carbon in the earth’s crust into heat-trapping carbon dioxide in the earth’s atmosphere. If carbon dioxide levels continue to rise at the rate they have in the last few years then we will hit 450 ppm in little more than twenty years. Four-hundred-fifty ppm is the level at which the probability of containing temperature increases to only 2 degrees Celsius drops to only 50 percent. Scientists and world leaders have identified 2 degrees as the global warming red zone, beyond which we tread at our rapidly escalating peril.

Previously I wrote about recent reductions in U.S. CO2 emissions and noted that President Obama’s target of reducing those emissions by 17 percent from 2005 levels is within reach. Why then are CO2 concentrations still rising?

There are two main reasons. The first is the rapidly increasing emissions from rapidly developing countries, particularly China. Emissions from Chinese factories, power plants and other sources have surged by more than 65 percent since 2005, while U.S. emissions dropped by 13 percent. Keep in mind, though, that their per capita emissions remain far below ours—7.2 metric tonnes in 2011, compared to 17.3 for us here—and cumulative emissions from China are still far below the U.S. total. (Moreover, a significant share of Chinese emissions come from producing goods that are consumed in the United States and other rich countries. About 20 percent of China’s emissions are related to producing exports, while Americans outsource about 10 percent of our emissions, according to Stanford researchers Steven J. Davis and Ken Calderia.)

The second reason that global carbon levels are surging is the unfortunate fact that carbon dioxide lingers in the atmosphere for as long as 100 years or more. To start stabilizing global CO2 concentrations we’re going to have to cut annual emissions by a lot and find good ways to absorb more of the CO2 that’s already been released.

Think about it this way: Imagine our atmosphere is a bathtub. If you’re filling the tub at 10 gallons a minute, and the drain leaks out only 2 gallons a minute—think of that as the amount of carbon the world’s forests and oceans absorb each year—then the level in the tub will climb pretty quickly. Even if you turn the faucet down by half, to 5 gallons a minute, the water level will continue to rise. Only by cutting levels by a whopping 80 percent—to 2 gallons a minute, the amount leaking out the drain—can you stabilize the water level and prevent dangerous overflow. Of course, you might also be able to open the drain wider. In the real world, that means reversing global deforestation—trees are made of carbon that has been sucked out of the atmosphere by photosynthesis. Unfortunately, deforestation, especially in tropical regions, is currently contributing about 10-20 percent of the total carbon emissions to the atmosphere

All that means that we’re going to have to do a lot to cut global emissions and global carbon concentrations. Not only are we going to need to cut carbon pollution from power plants, cars, trucks and planes, we’re going to have to protect and restore the world’s forests, if we want CO2 levels to stabilize and eventually reverse. So it’s no surprise (at least to carbon cycle scientists) that a modest reduction in U.S. emissions hasn’t translated into a reduction in the amount of carbon dioxide in the atmosphere.

But limiting warming to 2 degrees Celsius is still possible. And, luckily, some of the most effective strategies for cutting heat-trapping pollution internationally also offer the greatest public health benefits—like cutting black carbon by putting particulate filters on diesel engines, and capturing, rather than venting, methane during coal, oil and gas production. (Drew Shindell from NASA and an international team of 23 coauthors published an important paper on this subject in the journal Science last January.)

This week’s news about global atmospheric carbon levels climbing further in 2012 is sobering to be sure. But the good news is that an increasing number of Americans understand just what’s at stake, and just how important our efforts to cut carbon emissions are. New polling out from the Yale Project on Climate Change Communications finds that Americans are significantly more “alarmed” and “concerned” about global warming than we have been over the last four years. (And the Yale poll was taken in September, before Hurricane Sandy.) They are not alone. China is piloting carbon caps in seven regions and officials are considering capping total coal consumption and establishing a carbon tax. China may well move on these policies before the U.S. Congress does. Fortunately, there is much President Obama can do to continue reducing U.S. emissions using laws already on the books.

Three hundred and ninety five parts per million—this week’s news—reminds us, once again, that now is the time to act.

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Patrick LefebvreMar 8 2013 10:16 AM

You should have started your graph in 1998, and then added the average temperatures on top.

The correlation between co2 and temperature would have become very clear...

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