INCREASED PLANT-GROWTH IN THE NORTHERN HIGH-LATITUDES FROM 1981 TO 1991

Variations in the amplitude and timing of the seasonal cycle of atmosp heric CO2 have shown an association with surface air temperature consi stent with the hypothesis that warmer temperatures have promoted incre ases in plant growth during summer(1) and/or plant respiration during winter(2) in the northern high latitudes. Here we present evidence fro m satellite data that the photosynthetic activity of terrestrial veget ation increased from 1981 to 1991 in a manner that is suggestive of an increase in plant growth associated with a lengthening of the active growing season. The regions exhibiting the greatest increase lie betwe en 45 degrees N and 70 degrees N, where marked warming has occurred in the spring time(3) due to an early disappearance of snow(4). The sate llite data are concordant with an increase in the amplitude of the sea sonal cycle of atmospheric carbon dioxide exceeding 20% since the earl y 1970s, and an advance of up to seven days in the timing of the drawd own of CO2 in spring and early summer(1). Thus, both the satellite dat a and the CO2 record indicate that the global carbon cycle has respond ed to interannual fluctuations in surface air temperature which, altho ugh small at the global scale, are regionally highly significant.