Plants Prospering From Climate Change

By J.R. Pegg

WASHINGTON, DC, June 6, 2003 (ENS) - Climate change during the past two decades has improved conditions for much of the world's plant life and the Earth is now a greener place as a result, finds a new study published today. Global changes in temperature, rainfall and cloud cover have given plants more heat, water and sunlight in areas where climatic conditions once limited growth, according to the study jointly funded by the U.S. National Aeronautics and Space Administration (NASA) and the U.S. Department of Energy.

The study finds that in general, for the period 1982 to 1999, areas where temperatures restricted plant growth, it became warmer; where sunlight was needed, clouds dissipated; and where it was too dry, more rain fell.

Lead author Ramakrishna Nemani, a professor in the forestry school at the University of Montana, says the study indicates climatic changes is "the leading cause for the increases in plant growth over the last two decades."

The study, published today in the magazine "Science," is the first to take a global look at the impact of climate change on plant growth.

Conditions for plants improved throughout much of the world in the past two decades, and they have responded. (Photo courtesy Rainforest Action Network)

The researchers point to colliding conditions that helped trigger the increase. The two decades they examined were two of the warmest on record, contained three intense El Nino events along with changes in tropical cloudiness and monsoon dynamics. In addition, atmospheric carbon dioxide (CO2) increased 9.3 percent - a factor, Nemani said, but one that provided a "lesser contribution" to vegetation growth.

The researchers constructed a global map of the Net Primary Production (NPP) of plants from climate and satellite data of vegetation greenness and solar radiation absorption. The climate data for the calculations came from two independently derived 18 plus year satellite datasets from high tech radiometers on a National Oceanic and Atmospheric Administration satellite.

They explain NPP as the difference between the CO2 absorbed by plants during photosynthesis, and CO2 lost by plants during respiration. The global NPP increase was six percent from 1982 to 1999, with ecosystems in tropical zones and in the high latitudes of the Northern Hemisphere accounting for 80 percent of the increase.

The study reports that NPP increased significantly over 25 percent of the global vegetated area, but decreased over seven percent of the area. The researchers say this illustrates how plants respond differently depending on regional climatic conditions.

Growth in the Amazon rain forests accounted for nearly half the global increase found in the study, growth linked to reduced cloud cover and steady rainfall.

Improved conditions for plants in much of the world has improved food supplies for some, but researchers say it would be wrong to draw conclusions from the study about the long term implications of climate change. (Photo by L. De Matteis courtesy Food and Agriculture Organization)

The Earth may have become more rich and lush with vegetation over the past two decades, but coauthor Charles Keeling from the Scripps Institution of Oceanography in California cautions that the findings do not indicate whether these positive impacts are due to short term climate cycles or longer term global climate change.

The 36 percent increase in global population, Keeling said, overshadows the increases in plant growth. Over the period measured, the world's population grew from 4.45 billion to 6.08 billion.

The researchers stress that this study only looks at one part of how the Earth is responding to climate change, which they say is still not fully understood.

Scientists - and policymakers tasked with addressing climate change - are keen to determine how plants are responding, in particular to increased C02 levels. Humanity's emissions of C02 continue to rise and scientists are unclear how much of this increase can be offset by increased vegetation.

Many scientists believe emissions of greenhouse gases, in particular carbon dioxide, are the leading causes of climate change.

Previous studies indicated that the rising levels of CO2 correspond to more plant growth, but the researchers of this latest study say too many factors are at work to draw a clear conclusion given current evidence.