Study: ‘Global Warming’ Making Northern Hemisphere Greener

Published June 1, 2007

Rising carbon dioxide levels in the atmosphere, together with moderately warming temperatures, have caused a substantial greening of the Northern Hemisphere. That’s according to Craig Idso, founder and former president of the Center for the Study of Carbon Dioxide and Global Change, reporting in the March 14 issue of CO2 Science.

CO2, Climate Dominant Factors

Idso’s article summarizes research first reported in the December 2006 Geophysical Research Letters. In that study, five scientists at universities in France and the United States studied the spatial patterns of vegetation growth north of 25 degrees latitude (a line running east-west just south of the Florida Keys) between 1980 and 2000.

The five scientists reported, “The results indicate that changes in climate and atmospheric CO2 likely function as dominant controllers for the greening trend during the study period.”

Prior studies on variations in northern hemisphere vegetation taken from satellite data from 1981 to 1999 had shown vegetation had increased by 8 to 12 percent across North America and Eurasia during the time period.

“At the continental scale, atmospheric CO2, temperature, and precipitation account for 49%, 31%, and 13% of the increase in growing season LAI [Leaf Area Index], respectively,” the five scientists found.

Carbon Dioxide Benefits

Looking more deeply into the study, Idso reported, “In response to what climate alarmists describe as unprecedented increases in the air’s CO2 content and temperature, which they characterize as phenomena worse than nuclear warfare and global terrorism, the bulk of the terrestrial vegetation of the Northern Hemisphere north of 25ºN has not only not suffered because of them, it has actually grown more robust.”

There are “a number of biological consequences of elevated atmospheric CO2 concentrations,” Idso wrote.

“The best known of these important impacts is probably CO2’s aerial fertilization effect, which works its wonders on plants that utilize all three of the major biochemical pathways of photosynthesis (C3 [typical photosynthesis], C4 and CAM [C4 and CAM are photosynthesis adopted to arid conditions]),” Idso continued.

“In the case of herbaceous plants,” Idso noted, “this phenomenon typically boosts their productivities by about a third in response to a 300 ppm increase in the air’s CO2 content, while it enhances the growth of woody plants by 50% or more.”

Tropical Forest Trends

The new study reinforces prior scientific findings regarding a greening of the Earth during moderate warming since the late 1970s.

In 2005, NASA scientist Kazuhito Ichii led a team of scientists that reported in Global and Planetary Change on the interannual variability and trends in the productivity of tropical forests from 1982 to 1999.

After studying tropical forests in Africa, Asia, and the Amazon, the Ichii team reported, “recent changes in atmospheric CO2 and climate promoted terrestrial GPP [gross primary productivity] increases with a significant linear trend in all three tropical regions.”

Benefits Overlooked

“This is one of the little-talked about benefits of global warming,” said Iain Murray, a senior fellow at the Competitive Enterprise Institute. “Agricultural experts have long reported that the optimum temperature is actually warmer than it is today. They have also long told us that an increase in atmospheric carbon dioxide would benefit global plant life.

“The benefits of warmer temperatures are not restricted to plant life, either,” Murray added. “Another benefit is lower human mortality, [which is] associated with warmer temperatures. A warmer planet means fewer weather-related premature deaths.

“Global warming presents opportunities as well as challenges. Our goal should be to capitalize on the benefits of warmer weather while mitigating the potential challenges. It is an entirely realistic idea to capitalize on the benefits of a warmer climate,” Murray explained.

James M. Taylor ([email protected]) is managing editor of Environment & Climate News.