Rising temperatures reduce ability of plants to absorb carbon
Research shows warming over past decade caused droughts that reduced
number of plants available to soak up carbon dioxide.
Droughts have wiped out plants that would have absorbed the carbon
equivalent of all the man-made greenhouse gas emissions from the UK
every year.
Rising temperatures in the past decade have reduced the ability of
the world’s plants to soak up carbon from the atmosphere, scientists
said today.
Large-scale droughts have wiped out plants that would have otherwise
absorbed an amount of carbon equivalent to Britain’s annual man-made
greenhouse gas emissions.
Scientists measure the amount of atmospheric carbon dioxide absorbed
by plants and turned into biomass as a quantity known as the net primary
production. NPP increased from 1982 to 1999 as temperatures rose and
there was more solar radiation.
But the period from 2000 to 2009 reverses that trend ? surprising
some scientists. Maosheng Zhao and Steven Running of the University of
Montana estimate that there has been a global reduction in NPP of 0.55
gigatonnes (Gt). In comparison, the UK’s contribution to annual
worldwide carbon dioxide emissions was 0.56Gt in 2007, while global
aviation industry made up around 0.88Gt (three percent) of the world
total of 29.3Gt that year, according to UN data.
The researchers used data from the moderate resolution imaging
spectroradiometer (Modis) on board Nasa’s Terra satellite, combined with
global climate data to measure the change in global NPP over the past
decade.
“The past decade has been the warmest since instrumental measurements
began, which could imply continued increases in NPP,” wrote Zhao and
Running in the journal Science. But instead of helping plants grow,
these rising temperatures instead caused droughts and water stresses,
particularly in the southern hemisphere and in rainforests, which
contain most of the world’s plant biomass.
The growth there has been curtailed by lack of water and increased
respiration, which returns carbon to the atmosphere. These problems
counteracted any increases in NPP seen at the high latitudes and
elevations in the northern hemisphere.
Reduced plant matter not only reduces the world’s natural ability to
manage carbon dioxide in the atmosphere but could also lead to problems
with growing more crops to feed rising populations or make sustainable
biofuels.
“Under a changing climate, severe regional droughts have become more
frequent, a trend expected to continue for the foreseeable future,” said
the researchers. “The warming-associated heat and drought not only
decrease NPP, but also may trigger many more ecosystem disturbances,
releasing carbon to the atmosphere. Reduced NPP potentially threatens
global food security and future biofuel production and weakens the
terrestrial carbon sink.”
The researchers conclude that further monitoring will be needed to
confirm whether the decrease in NPP they have observed in the past
decade is an anomaly or whether it signals a turning point to a future
decline in the world’s ability to sequester carbon dioxide.
Guardian.co.uk |