More vegetation could speed up warming in the short term

Humans may be concerned about global warming, but nature for its part appears to be adapting.  A new study by a team of international experts examining the latest satellite and weather station data from The National Aeronautics and Space Administration (NASA) and The National Oceanic and Atmospheric Administration (NOAA) suggests that the rate of change in vegetation in middle Canada (the so-called boreal region) is leveling off, while the vegetation in the northernmost tundra is dramatically increasing during summer months.

I. Vegetation Growth is Rapidly Increasing in Permafrost Region

The vegetation in turn is causing a so-called "amplified warming" effect -- by the vegetation limiting the snow cover, which in turn provides a darker, less reflective surface that absorbs sunlight and traps heat.

The study, funded by NASA, finds that vegetation is effectively shifting northward approximately 7 degrees.  Dr. Compton Tucker a Senior Scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, comments, "As a result of the enhanced warming over a longer ground-thaw season, the total amount of heat available for plant growth in these northern latitudes is increasing. This created during the past 30 years large patches of vigorously productive vegetation, totaling more than a third of the northern landscape -- over 9 million km2, which is roughly about the area of the USA -- resembling the vegetation that occurs further to the south."

Plant growth
Plant growth in the Canadian permafrost region is dramatically increasing.
[Image Source: NASA]

Terry Callaghan a climatology Professor at the Royal Swedish Academy of Sciences and the University of Sheffield, UK, comments, "The reduction of vegetation seasonality, resulting in increased greenness in the Arctic, is visible on the ground as an increasing abundance of tall shrubs and tree incursions in several locations all over the circumpolar Arctic."

A clue to where vegetation growth will eventually reach may be found in the boreal, region where vegetation previously greatly increased, but is now leveling off.  The slowing of boreal growth is more pronounced in North America than in the Russian north.  Ultimately, the vegetation in the melting permafrost region is self-limiting, as it will saturate the more northern latitude.

II. Study Doesn't Consider Carbon Trapping Properties of Vegetation

Researchers warn that this trend may lead to increasing forest fires and droughts in boreal regions, where vegetation growth is slowing.  Using "17 state-of-the-art climate model simulations", the researchers predict that compared to the 1951-1980 reference period, the model suggests that by 2100 the net latitude shift could reach 20 degrees.

However, the researchers acknowledge that flat-lining temperatures over the last decade caused the models to overshoot vegetation estimates substantially.  Bruce Anderson a Professor of Earth and Environment at Boston University, remarks, "Since we don't know the actual trajectory of atmospheric concentration of various agents capable of forcing a change in climate, long-term projections should be interpreted cautiously."

permafrost melting
Extra vegetation may melt permafrost may decrease reflectivity and increase greenhouse gases, but it may also soak up carbon.
[Image Source: Vladimir Romanovsky]

The researchers suggest the change in vegetation growth regions could substantially impact the timber and agricultural industries.  They also are concerned that melting in the north could release pockets of methane and other greenhouse gases that are trapped in the permafrost.

One major oversight of the study is that it does not fully examine the ability of the extra vegetation to absorb atmospheric carbon.  It seems like that while a reduction in reflectivity certainly will amplify heating, that fresh plant growth will soak up carbon.  Ultimately, this means that if the north greens to the extent that the study predicts, the extra carbon trapping could substantially reduce ongoing warming.

The study was published in the prestigious peer-reviewed journal Nature: Climate Change.

Source: Boston University [PDF]

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