The terrestrial biosphere, a term that encompasses all living organisms on the land, is a contributor to climate change, according to a new study by Carnegie Institute scientists. For the first time ever, the team examined the net balance of the three major greenhouse gases - carbon dioxide, methane and nitrous oxide - for each region of Earth's landmasses.
Interestingly, the results revealed that human-induced methane and nitrous oxide emissions from ecosystems are much greater than the ability of the land to absorb carbon dioxide emissions, pointing to a necessary revision of our current view of the relationship between human activity and global warming.
"Typically we think of land as a net 'sink' of carbon dioxide," said Anna Michalak, co-author of the study. "But we found that the sign of the human-induced impact is reversed if we also take into account methane and nitrous oxide."
After examining the fluxes of the three greenhouse gases on land that stemmed from human activity over the last three decades, the team removed emissions that occurred naturally prior to human intervention.
The results were surprising - they found that human impact on biogenic methane and nitrous oxide surpassed the human impact on the terrestrial uptake of carbon dioxide, which means that that due to the actions of humans, the terrestrial organisms on the Earth are now contributing to climate change rather than helping control it.
The results run contrary to previous studies that only focused on carbon dioxide and suggested that human impacts on terrestrial carbon uptake have been beneficial.
Additionally, the study revealed that greenhouse gas emissions vary by region, with human-induced emissions of the gases in Southern Asia possessing a larger net warming effect compared to other areas. This likely stems from the large amount of methane emissions in this region from rice fields and livestock, as well as the nitrous oxide created by man-made fertilizers.
"This finding reveals for the first time that human activities have transformed the land biosphere to a contributor to climate change," said lead author Hanqin Tain.
"This study should serve as a wake-up call to governments, policymakers, and individuals around the world," Michalak concluded. "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."
The findings were published in the March 9 issue of Nature.
