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Climate in Context: August 20, 2010

By Alyson Kenward and Michael D. Lemonick

Extra CO2 May Not Be Such a Boon for Plants After All

Back in 2003, Steve Running, an ecologist and climate modeler at the University of Montana, co-authored a paper that analyzed changes in the uptake of carbon dioxide (CO2) by plants around the world (the technical term for this uptake is “primary production”). The paper showed that it had been increasing through the 1980s and 1990s. The reason, he says: “Warming global temperatures were leading to longer growing seasons” – which gave plants more time, on average, to suck in CO2.

Running and his Montana colleague Maosheng Zhao returned to the question recently, and since temperatures have continued to rise, says Running, “our hypothesis was that was that if you’re following the same logic, you should [see] a further enhancement in primary production.”

Instead, according to a new paper the pair authored in this week’s Science, there's been a trend reversal. Specifically, they found that while carbon uptake rose about six percent from 1982 to 1999, it’s since pulled back by about one percent.

“In higher latitudes,” Running says, “we’re still seeing lengthening of growing seasons.” Closer to the equator, though, and especially in the southern hemisphere, the warming has lead to major droughts – not exactly a recipe for healthy plants. What makes this study so compelling is that it was based on global satellite observations, not scattered local measurements. Running says it’s not clear, though, whether the declining trend in plant carbon uptake will continue.

“If the average precipitation stays the same and temperatures continue to rise,” he says, “the soil will get drier.” But while rising temperatures in most areas of the world are highly likely, changes in precipitation are more uncertain.

The study also weakens the argument that extra CO2 will invariably be beneficial to plants. Plants do need CO2 to grow, but if they don’t get other nutrients and adequate water, more CO2 won’t necessarily help.

Here’s a video from NASA that lays out the new results (click on this NASA graphic and scroll down the page):


 

A Step Forward for Solar Energy Conversion

One of the hottest areas of chemical research these days is the search for cheaper and more efficient materials to convert the sun’s energy into a form that humans can use. In addition to a the Powering the Planet consortium, funded by the National Science Foundation, there are a number of international research groups that are on the hunt for ways to harness the sun’s power to make carbon-free fuels.

A new paper published last week in Nature Chemistry gets one step closer to using solar power to split water into hydrogen and oxygen. Breaking up molecules of water requires an incredible amount of energy (if you just want to do it with heat alone, you would have to get it to about 3,000 degrees Celsius), but with the help of the right catalyst, researchers hope to make the process a bit easier. In this new study, researchers took two different types of known material, a metal catalyst and carbon nanotubes, and put them together to accomplish some of the best water-splitting activity ever observed. Turning this science into technology that can be scaled up to churn out lots of hydrogen fuel is still a number of years away, however.

If you want to get a better idea of why some chemists think solar power is best paired with water, take a look at this video of MIT chemist Dan Nocera from a 2009 PopTech conference.

 

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Urban vs. Rural Heat Cities tend to be warmer than the surrounding countryside, a phenomenon known as an urban heat island.

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