Plants grow well in a greenhouse, right?

As always, the answer depends on semantics. If by “greenhouse” one means a completely controlled, artificial environment, operated by human beings, i.e. a big machine for maintaining an optimal growing environment for particular types of plants, then the answer is, by definition, “yes”. If you mean the warming environment, where humans have triggered climate change and now Mother Nature and Father Physics are doing whatever the hell they damn well please, then the answer is an emphatic “no”.

Which is a roundabout way of pointing out yet another nasty surprise from the world of scientific research. Instead of being iteration number 8,374 of “it’s worse than we thought”, this one goes into the category of, “we thought it was better and it’s actually worse”.

Drought Drives Decade-Long Decline in Plant Growth:

Earth has done an ecological about-face: Global plant productivity that once flourished under warming temperatures and a lengthened growing season is now on the decline, struck by the stress of drought.

NASA-funded researchers Maosheng Zhao and Steven Running, of the University of Montana in Missoula, discovered the global shift during an analysis of NASA satellite data. Compared with a six-percent increase spanning two earlier decades, the recent ten-year decline is slight — just one percent. The shift, however, could impact food security, biofuels, and the global carbon cycle.

“We see this as a bit of a surprise, and potentially significant on a policy level because previous interpretations suggested that global warming might actually help plant growth around the world,” Running said.

“These results are extraordinarily significant because they show that the global net effect of climatic warming on the productivity of terrestrial vegetation need not be positive — as was documented for the 1980′s and 1990′s,” said Diane Wickland, of NASA Headquarters and manager of NASA’s Terrestrial Ecology research program.

Conventional wisdom based on previous research held that land plant productivity was on the rise. A 2003 paper in Science led by then University of Montana scientist Ramakrishna Nemani (now at NASA Ames Research Center, Moffett Field, Calif.) showed that global terrestrial plant productivity increased as much as six percent between 1982 and 1999. That’s because for nearly two decades, temperature, solar radiation and water availability — influenced by climate change — were favorable for growth.

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“This is a pretty serious warning that warmer temperatures are not going to endlessly improve plant growth,” Running said.

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“This past decade’s net decline in terrestrial productivity illustrates that a complex interplay between temperature, rainfall, cloudiness, and carbon dioxide, probably in combination with other factors such as nutrients and land management, will determine future patterns and trends in productivity,” Wickland said.

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“The potential that future warming would cause additional declines does not bode well for the ability of the biosphere to support multiple societal demands for agricultural production, fiber needs, and increasingly, biofuel production,” Zhao said.

“Even if the declining trend of the past decade does not continue, managing forests and croplands for multiple benefits to include food production, biofuel harvest, and carbon storage may become exceedingly challenging in light of the possible impacts of such decadal-scale changes,” Wickland said.

The article includes this illustration:

A snapshot of Earth’s plant productivity in 2003 shows regions of increased productivity (green) and decreased productivity (red). Tracking productivity between 2000 and 2009, researchers found a global net decrease due to regional drought. Credit: NASA Goddard Space Flight Center Scientific Visualization Studio

Yet again: The primary vector for the impacts of climate change on humanity will be water. Water for agriculture, personal use, and hydroelectric generation will all be threatened, thanks to shifts in rainfall patterns and the decline and disappearance of glaciers that provide summer water flows to critical parts of the world. Water will also do more damage from flooding, as seen in Pakistan, China, and parts of the US among others this year, and sea level rise that will threaten coastal cropland with salt intrusion.

The only real question is which specific effects will hit which parts of the world and in what order.

The results of this study shouldn’t be too great a surprise. We know that the Earth System is an extremely complex and highly interrelated set of subsystems, so we should expect to see cascading effects that result in opposing forces (e.g. warmer temperatures and longer growing seasons vs. drier conditions) with a net result not always to our liking. When you kick an essentially stable system as hard as we have by pushing the atmospheric CO2 level to roughly 390 ppm in such a short time (compared to that needed for species to adapt to a changing environment), you tip over a lot of dominoes, whether you know they exist or not.

In more concrete terms, this finding, assuming it’s held up by ensuing work[1], is very bad news.[2] As it becomes increasingly difficult to grow crops in some parts of the world, the impact of individual events, like the heat wave in Russia that’s expected to reduce their wheat production by one third, or about 35 million tons, will be greatly magnified. If some productive food growing areas of the world take a big hit when there’s a surplus of food worldwide, then we still have a sizable challenge to finance and deliver aid to the stricken area, but it can still be done. If that surplus is eroded by drought then our supply buffer will be reduced, possibly to dangerous levels. And at that point humanity suddenly is faced with some truly unpleasant questions.

[1] Speaking of other work, this isn’t the only very recent study that found climate change to be a less than universally favorable condition for plants and their CO2 uptake: Trees Soaking Up Less Carbon Than Expected, Study Finds

[2] Anyone here care to guess how long it will take the deniers to cherry pick the results and say that “a major study in Science found that Northern Hemisphere plants have continued to thrive” and conveniently overlook that the worldwide net plant productivity was down?