Savannahs Help Slow Down Climate Change

Savannahs, though they are not jam-packed with carbon-absorbing trees, nonetheless help to slow down climate change, according to a new study.

Tropical rainforests have long been considered Earth's most important carbon sinks, sequestering large amounts of carbon dioxide (CO2) from the atmosphere and thereby slowing down the increasing greenhouse gas effect. But scientists now report in the journal Science that the vast extensions of semi-arid landscapes - including savannahs and shrublands - actually dominate other global ecosystems in carbon capture.

"Understanding the processes responsible for trends and variability of the carbon cycle, and where they occur, provides insight into the future evolution of the carbon sink in a warmer world and the vital role natural ecosystems may play in accelerating or slowing down human-induced climate change," Anders Ahlström, from Lund University and Stanford University, who led the study, said in a statement.

That's not to say that tropical rainforests aren't crucial in the fight against climate change. These ecosystems are highly productive, and fight carbon even better than we hoped, taking the harmful greenhouse gas from our atmosphere at unprecedented rates. However, the downside is that rainforests are extremely crowded with little room to fit in more photosynthesizing plants that can store carbon. In addition, the typical moist, hot weather conditions are ideal for growth and do not change much from year to year.

In savannahs, on the other hand, increased productivity actually makes more room for trees whose growing biomass provides a sink, or store, for carbon sequestered from the atmosphere. In addition, savannahs spring to life in wetter years, causing large fluctuations in CO2 uptake between wet and dry years - large enough, in fact, to control the amount of CO2 in the atmosphere.

"There has been an increase in the uptake of carbon dioxide over time, and land ecosystems have together absorbed almost one third of all carbon dioxide emissions from human activity since the 1960s. What is perhaps even more surprising is that this trend is also dominated by the semi-arid lands," Ahlström said.

It is well known that humanity has to boost its efforts to curb tropical deforestation, as it triggers changes that are just as costly as carbon pollution. But, with this study, the researchers show that we can no longer ignore the semi-arid regions of the world.

"The world's semi-arid regions will become even more important in the future as climate variability and extremes increase in a warmer world," explained Australia-based researcher Josep G Canadell, director of the Global Carbon Project. "The extensive semi-arid regions of the world are emerging as a growing force in shaping the functioning of our planet," he continued.

"This study brings out clearly the importance of directing attention towards savannahs and other dry-climate ecosystems that have been largely neglected so far in climate policy discussions, and that moreover characterize the landscapes of some of the poorer countries of Earth," concluded Benjamin Smith, Professor of Ecosystem Science at Lund University.

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