Drought Drives Decade-Long Decline in Plant Growth NASA
8.19.10
http://www.nasa.gov/topics/earth/features/plant-decline.html (also vide0)
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
Added image shows the best
food producing regions of
the world. Peter Carter
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.
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 discovery comes from an analysis of plant productivity data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on
NASA's Terra satellite, combined with growing season climate variables including temperature, solar radiation and water. The plant and
climate data are factored into an algorithm that describes constraints on plant growth at different geographical locations.
For example, growth is generally limited in high latitudes by temperature and in deserts by water. But regional limitations can vary in
their degree of impact on growth throughout the growing season.
Zhao and Running's analysis showed that since 2000, high-latitude northern hemisphere ecosystems have continued to benefit from
warmer temperatures and a longer growing season. But that effect was offset by warming-associated drought that limited growth in the
southern hemisphere, resulting in a net global loss of land productivity.
"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.of net primary production and the carbon cycle.
Researchers are keen on maintaining a record of the trends into the future. For one reason, plants act as a carbon dioxide "sink," and
shifting plant productivity is linked to shifting levels of the greenhouse gas in the atmosphere. Also, stresses on plant growth could
challenge food production.
"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 decadalscale changes," Wickland said.
Food production implications.
That changes (very much for the worse) all the climate crop model results showing small increases in temperate region cereal
production up to 3.5C local (3C global). This NASA study shows all the worlds agricultural regions are in negative natural plant
productivity regions. This suggests that for global food production the assumed benefit to agriculture of CO2 increase fertilization effect
will not materialize and yields will go into decline globally at much less than the local 3.5C increase from 1900 (@3C global) that the
IPCC reported.
The Peter Cox 2000 Terrestrial Carbon Feedback Paper and the Amazon
This would indicate that the terrestrial carbon feedback from the Peter Cox model published in 2000 (next page) was right. The 2000
Hadley model experiment gave an additional 1.5°C global temperature increase by 2100 from green plant and soil carbon feedback
emissions, carbon being taken up by global plant mass, a huge temperature change. The Cox model gave an irreversible die back of
the Amazon by 2050, which is supported by the NASA plant production record.
.
Nature 408, 184-187 (9 November 2000) | doi:10.1038/35041539 September 2000
o
Peter M. Cox, Richard A. Betts, Chris D. Jones, Steven A. Spall, Ian J. Totterdell
Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate modelPeter M.
Cox1, Richard A. Betts, Chris D. Jones1, Steven A. Spall & Ian J. Totterdell2 Hadley Centre, The Met Office,
Abstract
The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to
significant changes in climate1. About half of the current emissions are being absorbed by the ocean and by land ecosystems2, but
this absorption is sensitive to climate3, 4 as well as to atmospheric carbon dioxide concentrations5, creating a feedback loop. General
circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and
CO2 concentrations from simple carbon-cycle models that do not include climate change6. Here we present results from a fully
coupled, three-dimensional carbon–climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate
change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall
carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the
terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in
uncoupled carbon models2, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.