New research confirms increased greening

Greening seems to have increased during the 1980s and 1990s in the northern hemisphere from the arctic regions down to the 35th parallel of latitude (roughly southern Europe). This has been shown by measurements from space satellites. Some observers, however, have doubted the reliability of these measurements. In the latest issue of Science, a research team from the Institute for Climatic Impacts Research in Potsdam, the Max Planck Institute for Biogeochemistry in Jena, and Lund University presents new findings that support the satellite observations.

The research team has fed in the current values for temperature, precipitation, solar radiation, cloud cover, and carbon dioxide content during the period 1982-1998 in a model for vegetation growth. It is called the LPJ Model and was developed at Lund by Colin Prentice, Stephen Sitch, and Ben Smith. Of the three, the former two are now in Jena, whereas ecologist Benjamin Smith is associated with the Department of Physical Geography and Ecosystem Analysis at Lund University in Sweden.

Vegetation has been measured from space using AVHRR, Advanced Very High Resolution Radiometry. This is a spectroscopic method that can register when light reflects from the surface of green leaves.

“During the 1980s and 1990s the temperature increased somewhat. Satellite measurements show a continuous increase in greenery with the exception of 1991-92, when green vegetation dipped a bit and then began to grow again. In 1991 the volcano Pinatubo in the Philippines had its huge eruptions. The number of particles rose in the atmosphere. This had a cooling effect,” says Ben Smith, adding:

“Critics maintained that since these changes were subtle, they could just as likely have been caused by an effect of the statistical processing of the material. Moreover, according to critics, the dip when Pinatubo erupted could be a measurement error since the increase in particulates in the atmosphere affected spectra from the earth.

“But what we now see is that the model yields the same picture as the AVHRR measurements including the change when Pinatubo was active. This congruence of results reinforces the satellite measurements and at the same time provides confirmation that our model works properly. What the satellite measurements probably react to are changes in the greenery of deciduous trees. The change can be due to longer seasons of growth, which allow leafy trees to turn green earlier in the spring,” concludes Ben Smith.