Climate changes making planet greener
By Richard Stenger
(CNN) -- The Earth has become significantly greener over the past two decades, the result of climate changes that have furnished plants with more heat, light, water and carbon dioxide, according to a new Science magazine report.
The overall plant bulk went up about 6 percent over much of the planet, with spikes in the tropics and high latitudes of the Northern Hemisphere accounting for 80 percent of the gains, researchers said.
The years since 1980 included two of the warmest decades on record, producing changes that have boosted growth ingredients in regions where they might otherwise have been scarce.
A 9.3 percent increase in the greenhouse gas carbon dioxide, a de facto fertilizer, was significant, but not enough to produce by itself the kind of vegetative growth, the study found.
Not everywhere has become more vegetated. About 7 percent of the studied landmasses experienced drops in plant productivity.
"The biggest winners [becoming more green] seem to be India, Brazil and Canada," said lead author Ramakrishna Nemani. "Losers are parts of Mexico and northern Siberia [drying and cooling, respectively]."
The Amazon rain forest alone was responsible for more than 40 percent of the plant growth, mostly due to reduced cloud cover that let in more sunshine.
"The most surprising result is that of the Amazon," said Nemani, a forestry professor at the University of Montana in Missoula.
The South American rain forest has suffered from deforestation on the edges in recent decades, but the interior sections have grown vigorously, he said.
"Much of this increased growth has been attributed to carbon dioxide," Nemani said. "What we found is that changes in cloud cover may be a better explanation."
The study, funded by NASA and the Department of Energy, includes decades worth of satellite and ground data, which the research team studied for nearly a year and a half to determine plant productivity.
"Productivity [refers to] how much carbon ends up stored in the biomass -- roots, trunks and leaves -- of plants after they tally up carbon gains through photosynthesis and carbon losses through respiration [the plant version of an exhalation]," said Rebecca Lindsey, a spokeswoman with NASA's Earth Observatory in Greenbelt, Maryland.
Report co-author Charles Keeling, a carbon cycle specialist at the Scripps Institution of Oceanography in La Jolla, California, said the ultimate cause could be short-term climate patterns or long-term global climate shifts.
Whether humans have contributed much to the greening trend remains unknown, but co-author Ranga Myneni cautions that we should hold off on congratulating ourselves on our green thumbs.
"[Plant] productivity may have increased 6 percent in the last 18 years, but human population has increased by over 35 percent over that same time," the Boston University geographer said.
"These ... changes have not improved global habitability in any significant way."