A study by an international research team published today in the journal Nature finds that human activities result in significant emissions of greenhouse gases from land to the atmosphere.
Global climate change is caused primarily by CO2 emissions from human use of fossil fuels (coal, oil, and natural gas). Deforestation, especially in the tropics, is also an important source of CO2 emissions. But on the whole, land absorbs CO2 from the atmosphere, primarily because of regrowth of mid-latitude forests. This study shows, however, that when two other greenhouse gases (methane and nitrous oxide) are taken into account, human activities on balance result in a strong warming influence from land.
The research team, comprised of 23 scientists from 16 institutions in four countries, was led by Prof. Hanqin Tian of Auburn University, who notes that “this finding reveals for the first time that human activities have transformed the land biosphere to act as a contributor to climate change.”
According to contributing author and WHRC scientist Christopher Schwalm, “Our study is a synthesis of numerous independent state-of-the-art biosphere-atmosphere flux estimates of the three greenhouse gases with a biogenic cycle: CO2, methane, and nitrous oxide. This is unprecedented in that it goes beyond CO2 to include other, arguably, more potent greenhouse gases.”
The researchers also show that the net effect of these three gases varies by region. In Southern Asia, a region including China and India, the net climate warming effect is largest. As one of the authors notes, “a reduction in agricultural methane and nitrous oxide emissions in particular in Southern Asia may help mitigate climate change.”
Says another contributor, the findings are “a big wake-up call for the global climate community” in that business-as-usual land management is not sustainable to mitigate global warming.
Adds Dr. Schwalm, “Our results show that the cumulative effect of post-industrial anthropocentric activities on the land biosphere act to exacerbate global change.”
WHRC is an independent research institute where scientists investigate the causes and effects of climate change to identify and implement opportunities for conservation, restoration and economic development around the world.