Screaming trees: latest research points to serious decline in plant growth during last decade

You will find something more in woods than in books. Trees and stones will teach you that which you can never learn from masters.
~ Saint Bernard

Looking back, I think many of will regard 2010 as a watershed year for the climate change debate.  

Back in January “Climategate” and the collapse of COP15 seemed the most pressing issues.

Either we were fighting a desperate rear-guard action defending the reputation of scientists and the credibility of science, or coming to terms with the failure of the talks at Copenhagen.  

However, once the Climategate affair began its slow decline into obscurity we became alert to a more serious issue: a rapidly worsening climate and declining ecosystems.  

It’s bad enough that the seas are dying – viz the 40% reduction in phytoplankton since 1950. It’s troubling that city sized chunks of Greenland’s glaciers are falling into the sea. We looked on in horror as Russia burned while Pakistan drowned.  

A “positive” is that many previously sceptical journalists and commentators are now accepting the reality of climate change. I regard these as the first signs of the denial movements very own “death spiral” (a decline set to match that of the Arctic ice).  

The tragedy of course is that the forces of delay, denial and confusion where allowed to mislead the public for so long.  

Back to the emerging science…  

Last week science delivered another body blow.  

Latest research by scientists from NASA points to a ten year decline in plant growth across the globe (abstract of paper here):

Terrestrial net primary production (NPP) quantifies the amount of atmospheric carbon fixed by plants and accumulated as biomass. Previous studies have shown that climate constraints were relaxing with increasing temperature and solar radiation, allowing an upward trend in NPP from 1982 through 1999. The past decade (2000 to 2009) has been the warmest since instrumental measurements began, which could imply continued increases in NPP; however, our estimates suggest a reduction in the global NPP of 0.55 petagrams of carbon. Large-scale droughts have reduced regional NPP, and a drying trend in the Southern Hemisphere has decreased NPP in that area, counteracting the increased NPP over the Northern Hemisphere. A continued decline in NPP would not only weaken the terrestrial carbon sink, but it would also intensify future competition between food demand and proposed biofuel production.

NASA has a very good page here, including video.  

The press release accompanying the publication of the paper notes some worrying trends:

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 favourable for growth.

Setting out to update that analysis, Zhao and Running expected to see similar results as global average temperatures have continued to climb. Instead, they found that the impact of regional drought overwhelmed the positive influence of a longer growing season, driving down global plant productivity between 2000 and 2009. The team published their findings Aug. 20 in Science.

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

The positive impact of more CO2 in the atmosphere is being overwhelmed by the increased frequency and duration of droughts.   Said one of the paper’s authors:

“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.

Translation: current agricultural practices, increasing demand for food and the belief that switching to biofuel (such as ethanol derived from corn) may not be possible.  

For all those who tout the “CO2 is plant food argument” consider there fact that H2O is vital to plant growth.  

Without it they simply don’t grow.  

Instead, they whither away in the blazing sun.  

[Hat tip Climate Progress]


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