Washington, Jan 3: A new study has discovered that autumns getting warmer because of global warming might make plants less efficient at keeping the greenhouse gas carbon dioxide out of the atmosphere.

According to a report in the National Geographic News, Earth's so-called carbon sinks—soil, vegetation, and oceans—currently absorb about half of the carbon dioxide that humans produce by burning fossil fuels.

While some data suggest that warmer springs in the Northern Hemisphere would allow plants to absorb more carbon, new research suggests that warmer autumns would offset or even trump any such gains.

"Warming autumn will enhance carbon loss from terrestrial ecosystems," said Dr. Shilong Piao, the lead author of the study.

During photosynthesis—the process by which plants convert sunlight into energy—plants absorb carbon and combine it with water to produce carbohydrates.

But vegetation also produces carbon dioxide during the decay of plant matter and during respiration, in which plants use oxygen to create energy and release CO2 as a waste product.

In warm months, when growth rates are high, an ecosystem with lots of vegetation may act as a greenhouse gas-trapping carbon sink. But during colder periods, respiration can outweigh absorption, and the same plants may become a net source of atmospheric carbon dioxide.

Using computer modeling to integrate forest canopy measurements and remote satellite data, researchers found that while warm spring temperatures accelerate growth more than soil decomposition and enhance carbon uptake, autumn warming greatly increases soil decomposition and significantly reduces carbon uptake.

“The effect of warmer autumns may have to do with soil moisture. In the fall, soil is typically drier, and perhaps the plants are done with the majority of their growth," said John Miller, of the National Oceanic and Atmospheric Administration in Boulder, Colorado.

"So the warmth in fall may be benefiting the microbes in the soil, which are busy spewing out CO2 as they chew on old plant parts, much more than the plants," he added.

If springs and autumns continue to warm, longer growing seasons could alter the absorption rates of each season—with uncertain results for the total amount of atmospheric CO2.

Over the past two decades, autumn temperatures in northern latitudes have risen by about 1.1 °C with spring temperatures up by 0.8 °C.

“The potentially rapid decline in the future ability of northern terrestrial ecosystems to remove atmospheric carbon dioxide would make stabilization of atmospheric CO2 concentrations much harder than currently predicted,” said Philippe Ciais, a member of the research team and a scientist from the Global Carbon Project. (ANI)