Warming Climate, Greening Earth, Carbon Sink

INTRODUCTION: Satellite observations over the past two decades indicate a trend towards longer grow-ing seasons and greater annual net primary production (NPP) in high latitudes. Using a dynamic vegetation model that predicts leaf area index (LAI), primary production and net ecosystem carbon exchange from first principles, we show that the trend and variability in the satellite observations are quantitatively consistent with independent climate data, and qualitatively with net ecosystem carbon exchange independently calculated from atmospheric CO2 concentration measurements.

We analyze data for 1982-1998, for which we had access to both climate and satellite data. A previous analysis of ten years of data from the Advanced Very High Resolution Radiometer (AVHRR) indicated a progressive greening of the boreal zone. A steady increase in annual maximum LAI during 1981-1991 was associated with a slight advance of spring budburst and delay of autumn abscission. Subsequent work spanning 1981-1999 has confirmed these findings but because of the need for data corrections for instrumental and navigational drift, intercalibration of successive instruments and consideration of aerosol effects, doubts about the validity of the trend have persisted. Such doubts could be dispelled if the interannual variations in greenness and growing season length were shown to be quantitatively consistent with independent expectations based on climate variability, and/or with independent reconstructions of changes in regional CO2 balance. This analysis employs a climate-driven terrestrial carbon cycle model capable of simulating the interannual variability of LAI and the components of the terrestrial carbon balance.

For background information on northern latitude greening and its implications for the terrestrial carbon cycle, follow the links below.

Earth is Becoming a Greener Greenhouse

Biomass Carbon Stocks, Sources & Sinks