What was done
The authors derive trends in China's terrestrial net primary production (NPP) from 1982 to 1999 based on satellite-derived Normalized Difference Vegetation Index (NDVI) data, contemporary climate data, and the Carnegie-Ames-Stanford Approach (CASA) satellite-based carbon model, as well as ground-based information on vegetation and soils.

What was learned
Piao et al. say their results suggest that "terrestrial NPP in China increased at a rate of 0.015 Pg C yr^-1 over the period 1982-1999, corresponding to a total increase of 18.5%, or 1.03% annually."  They also found that "during the past 2 decades the amplitude of the seasonal curve of NPP has increased and the annual peak NPP has advanced," which they say "may indirectly explain the enhanced amplitude and advanced timing of the seasonal cycle of atmospheric CO2 concentration (Keeling et al., 1996)," the former of which phenomena they further suggest "was probably due to the rise in atmospheric CO2 concentration, elevated temperature, and increased atmospheric N and P deposition," while the latter phenomenon they attribute to "advanced spring onset and extended autumn growth owing to climate warming."  We are in basic agreement on most of these points, but note that the advanced onset of what may be called biological spring is also fostered by the ultra-enhancement of early spring growth that is provided by the ongoing rise in the air's CO2 concentration (see Trees (Early Spring Growth) in our Subject Index).

What it means
Citing a total of 20 scientific papers at various places in the following quote, Piao et al. conclude that "results from observed atmospheric CO2 and O2 concentrations, inventory data, remote sensing data, and carbon process models have all suggested that terrestrial vegetation NPP of the Northern Hemisphere has increased over the past 2 decades and, as a result, the northern terrestrial ecosystems have become important sinks for atmospheric CO2."  Again, we agree, and wonder what there is about these very impressive positive observations that inspire radical environmentalists to classify the twin evils of rising atmospheric CO2 and temperature as worse than nuclear warfare and global terrorism.

Reference
Keeling, C.D., Chin, J.F.S. and Whorf, T.P.  1996.  Increased activity of northern vegetation inferred from atmospheric CO2 measurements.  Nature 382: 146-149.