This is the first study to specify the extent to which plants have prevented climate change since pre-industrial times.
Researchers based at Princeton University found that land ecosystems have kept the planet cooler by absorbing billions of tons of carbon, especially during the past 60 years.
The planet's land-based carbon "sink" - or carbon-storage capacity - has kept 186 billion to 192 billion tons of carbon out of the atmosphere since the mid-20th century, the researchers said.
From the 1860s to the 1950s, land use by humans was a substantial source of the carbon entering the atmosphere because of deforestation and logging.
After the 1950s, however, humans began to use land differently, such as by restoring forests and adopting agriculture that, while larger scale, is higher yield.
At the same time, industries and automobiles continued to steadily emit carbon dioxide that contributed to a botanical boom.
Although a greenhouse gas and pollutant, carbon dioxide also is a plant nutrient.
Had Earth's terrestrial ecosystems remained a carbon source they would have instead generated 65 billion to 82 billion tons of carbon in addition to the carbon that it would not have absorbed, the researchers found.
That means a total of 251 billion to 274 billion additional tons of carbon would currently be in the atmosphere.
That much carbon would have pushed the atmosphere's current carbon dioxide concentration to 485 parts-per-million (ppm), the researchers report - well past the scientifically accepted threshold of 450 (ppm) at which the Earth's climate could drastically and irreversibly change. The current concentration is 400 ppm.
Those "carbon savings" amount to a current average global temperature that is cooler by one-third of a degree Celsius (or a half-degree Fahrenheit), which would have been a sizeable jump, the researchers report.
The planet has warmed by only 0.74 degrees Celsius (1.3 degrees Fahrenheit) since the early 1900s, and the point at which scientists calculate the global temperature would be dangerously high is a mere 2 degrees Celsius (3.6 degrees Fahrenheit) more than pre-industrial levels.
The study is published in the Proceedings of the National Academy of Sciences.
--ANI (Posted on 17-10-2013)