New studies on nature slowing impacts of climate change
African Savannah. An international study shows that semi-arid ecosystems–savannahs and shrublands–play an extremely important role in controlling carbon sinks and the climate-mitigating ecosystem service they represent. Credit: © tellmemore / Fotolia
Posted: 21 May 2015 11:41 AM PDT
Tropical rainforests have long been considered the Earth’s lungs, sequestering large amounts of carbon dioxide from the atmosphere and thereby slowing down the increasing greenhouse effect and associated human-made climate change. Scientists in a global research project now show that the vast extensions of semi-arid landscapes occupying the transition zone between rainforest and desert dominate the ongoing increase in carbon sequestration by ecosystems globally, as well as large fluctuations between wet and dry years. This is a major rearrangement of planetary functions.
An international study released this week, led by Anders Ahlström, researcher at Lund University and Stanford University, shows that semi-arid ecosystems–savannahs and shrublands–play an extremely important role in controlling carbon sinks and the climate-mitigating ecosystem service they represent. “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,” says Anders Ahlström. Tropical rainforests are highly productive, and this means that they take up a lot of carbon dioxide, but rainforests are crowded places with little room to fit in more plants to do more photosynthesis and to 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 it is different. As productivity increases there is room to fit in more 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 carbon dioxide uptake between wet and dry years. Large enough, Ahlström and colleagues show, to control the amount of carbon dioxide 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,” Anders Ahlström says. We have long known that we need to protect the rainforests but, with this study, the researchers show that a heightened effort is needed to manage and protect the semi-arid regions of the world as well….
Ning Zeng et al. The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink. Science, May 2015 DOI: 10.1126/science.aaa1668