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Wednesday, June 10, 2015

Climate Change Won't Make Plants Grow Faster

One of the tenets of climate change deniers is that as the world warms -- when they admit that it is warming -- plants will grow more quickly. It turns out, not surprisingly, that's a lie:
“There is more to climate change than just temperature,” says Camilo Mora, an assistant professor of geography at the University of Hawaii in Mānoa, who led the work. Drought and limited sunlight will undermine any gain from a warmer atmosphere. By 2100, Mora says, “there could be an 11 percent reduction in the plant growing season worldwide.”
Specifically:
One primary reason is that heating the Arctic will not bring pineapples to Alaska. There is insufficient sunlight year-round at high latitudes to support lush vegetation. In addition, the tropics will lose up to 200 “suitable growing days” a year—days when temperature, soil moisture and sunlight favor growth rather than retard it—because of excessive heat and drought. Overall, “the decreasing number of suitable growing days in the tropics will offset optimistic projections at mid- and high-latitudes,” the study concludes. 
And the idea that increased carbon dioxide levels will make plants grow faster because it's "plant food?" Not true.
Greater levels of CO2 made no difference one way or the other. At higher temperatures plants open their pores, called stomata, to capture the elevated CO2, which boosts photosynthesis, greening the leaves. But plants also tend to close their stomata in warmer temperatures to prevent water loss. Mora says that on balance the two effects cancel out.
Plants don't like extreme heat, and just like people, they die when they get too hot. There's a reason that the hottest places in the world -- deserts -- have so few plants.

The interesting thing is that the study was instigated by climate deniers:
Mora did not expect this result when he began the study, inspired by notes he swapped with a climate denier. In 2013 Mora published a high-profile study in Nature showing that climate change would harm plants and animals in the tropics sooner than it would hurt them in the Arctic. He says he received numerous e-mails and phone calls attacking the results. “In one such phone call I decided to talk to the person,” he explains. “The guy, one of the so-called climate deniers, claimed that climate change would actually be good for the planet.” The argument is known as the greening effect—that warmer temperatures and higher CO2 levels in the atmosphere would increase plant growth. Mora found several serious papers reaching that conclusion.
But Mora, who grew up in Colombia and saw plants struggle under high heat and low rainfall, had a hunch that there was more to the story. He and his graduate students calculated the number of days, from now through 2100, when plants would have favorable temperature, moisture and light to grow. They found that at high latitudes plants in the future could not “profit” from warmth because sunlight is limited much of the year. In the tropics temperatures got too hot for numerous plants and drought rose, adding stress to already overtaxed ecosystems. Broadleaf forests there would take the biggest hit, losing as much as three months of suitable growing days annually. 
Nonetheless, Mora sees an upside to climate deniers:
Mora sees two big lessons from the new analysis. One, “that nothing good can come from messing with the Earth’s climate.” And two, “that engaging climate deniers could be good for scientific productivity.” 
If climate deniers were all just harmless cranks making scientists cross their t's and dot their i's, that would be one thing. But when they're employees and shills for oil and coal companies that spend billions of dollars suppressing and distorting the truth, dictating government policy and sucking up hundreds of billions of our tax dollars through direct and indirect subsidies, it's a whole other can of worms.

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