Warming-enhanced Plant Growth in the NorthSince 1980s: A Greener Greenhouse?NASA GSFC Biospheric Sciences Branch1 Department of Geography, Boston University2

1Compton J. Tucker and Daniel Slayback 2Liming Zhou, Robert K. Kaufmann, and Ranga B. Myneni

Has Vegetation Responded to Climate Change?

Overall warming in Eurasia. Lower warming and even cooling in North AmericaContinental Differences in Warming Land surface April-October temperature trends in C/18 yrs between 1982 and 1999 (NASA GISS Station Temperature data)

GIMMS NDVI

15-day composite NDVI data at 8 km resolution (07/81-12/99)

improved calibration

corrections for stratospheric aerosol effects from El Chichon and Mt. Pinatubo eruptions

Study Region

Vegetated pixels between 30N-70NObjectives

minimize the effect of Solar Zenith Anglereduce background effects (snow, barren and sparsely vegetated areas)use data from the same pixels in the entire analysis.

Changes in Vegetation ActivityChanges in vegetation activity can be characterized through

changes in growing season

changes in seasonal NDVI magnitude Increases in NDVI magnitudeIncreases in growing season IncreaseNDVI

Longer Growing Seasons(Increased by 18 Days)(Increased by 12 Days)11.9 days/18 yrs (p

Increases in April-October NDVI Magnitudes(8 Percent Increase)(12 Percent Increase)8.4/18 yrs (p

Spatial Pattern of April-October NDVI Changes

Persistence index: an index for identifying regions where NDVI has increased consistentlyA persistent increase in NDVI is observed in Eurasia over a broad contiguous swath of land while North America shows a fragmented pattern of change.

April-October NDVI trend at the 5% significance levelPixels that show a statistically significant trend are also pixels with high persistence.

April-October NDVI difference between 1995-99 and 1982-86 averagesPixels that show a large NDVI increase are also pixels with high persistence and statistically significant trends.

Consistency between April-October NDVI and Temperature R=0.79 (p

Statistical ResultsA statistically meaningful relation between NDVI and temperature is seen in both North America and Eurasia.No relationship between Eurasian NDVI and North American temperature or between North American NDVI and Eurasian temperature.

yxA statistically meaningful relation?y = 0 +1 x + y = 0 +1x+ 2 time + y =0+ 1 x + EA NDVIEA TyesyesyesNA NDVINA TyesyesyesEA NDVINA TnononoNA NDVIEA Tnonono

Conclusions

Eurasia is photosynthetically more vigorous than North America during the past two decades:

Eurasia has a higher percentage of vegetated pixels (61% vs. 30%) showing a larger increase in the NDVI magnitude (12% vs. 8%) and a longer active growing season (18 vs. 12 days) than North America.

The temporal changes and continental differences in NDVI are consistent with land surface temperature, an important determinant of biological activity.

Economic implications: warmer planet, greener north.

Press Coverage

Earth is Becoming a Greener Greenhouse(NASA, AGU and BU Joint Release Sep-4-2001)

TV (ABC, BBC, CNN, MSNBC etc.)Broadsheets (Hundreds)Radio (NPR, VOA, BBC, etc.) Wires (AP, Reuters, etc.)Internet News Magazines (about a hundred) Magazines (Science, Sci. Am., Natl. Geog., Popular Science, etc.)Countries: 20Web site hits: 9084 as of Oct 25

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