For the first time, scientists have assessed the net balance of the three main greenhouse gases — nitrous oxide, methane and carbon dioxide — for every continent on the planet, drawing the conclusion that human-produced emissions of nitrous oxide and methane overwhelmingly outstrip the Earth's natural ability to, in turn, absorb carbon dioxide emissions.
Every year the Earth's biosphere absorbs around a quarter of all of the carbon dioxide emissions produced by humans, which helps to regulate the warming effects caused by human activities like deforestation and burning fossil fuels.
But as revealed by a research report published this week, scientists worldwide have discovered that since 1981 alterations in land management have led to the production of more greenhouse gases than can be naturally absorbed by forests.
One of report's co-authors, Pep Canadell from Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) and member of the Global Carbon Project, explained that the researchers analyzed the amounts of methane and nitrous oxide that were produced globally between 1981 and 2010.
"When we bring other gases like methane and nitrous oxide, [which] come largely from our food system, what we saw is that the overall way we manage our biosphere, our global lands, have made those global lands to be a very large source of greenhouse gas," he said.
The team of 22 researchers, hailing from the U.S., the U.K., France and Australia, noted that since emissions of methane gas are produced by livestock, and nitrous oxide is widely used in fertilizers, one way to tackle the problem would be to monitor agricultural emissions.
"We need to rethink about ways that we're going to continue feeding the current population, the growing population, but even more importantly a population that is more interested in meat rich diets," Canadell said.
The study also found that greenhouse gas emissions vary substantially by region. For example, human-induced emissions in Southern Asia, including China and India, had a larger net warming impact in comparison to other regions. Southern Asia holds 90 percent of the world's rice fields and accounts for more than 60 percent of the world's nitrogen fertilizer use.
"Forests continue to be an active ally for us in terms of helping us to slow down climate change, it's just that we had not realised enough that all the other things we were doing to the land have consequences for other greenhouse gases above and beyond carbon dioxide," noted Canadell, but ultimately, "when we consider all gases together, methane and nitrous oxide are actually overwhelming, by two times, the good effect of the forest[s] removing carbon pollution."
Co-author Anna Michalak, from Carnegie's Department of Global Ecology, said, "This study should serve as a wake-up call to governments, policymakers, and individuals around the world," concluding that "we must expand our focus and devise strategies that target the biogenic emissions of these other greenhouse gases if we are to change the course of climate change."
