Emissions of the greenhouse gas methane from lakes and reservoirs risk doubling by the end of the century due to climate change according to a new study from Linköping University, Sweden, and NASA Ames Research Center in the US. This in turn could raise Earth’s temperature more than suggested by the UN climate panel IPCC’s current worst-case scenario.

“This study makes it even clearer that we really, really want to change the climate scenario as quickly as possible. The future will be very uncertain if we don’t,” says Professor David Bastviken at Linköping University, Sweden.

Lakes and water reservoirs are some of the largest sources of methane on Earth. The methane emitted is largely formed as microorganisms decompose organic matter in oxygen-free environments. Before industrialisation, natural methane emissions to the atmosphere were in balance with the methane breakdown processes. If the ongoing climate change disturbs the natural balance causing emissions to increase, global warming is at risk of worsening.

Together with Matthew S. Johnson, Research Scientist at NASA Ames Research Center, David Bastviken has created a model to predict changes in methane emissions from lakes and reservoirs until the end of the century based on IPCC climate scenarios. The model is based on real data from 767 locations in all Earth’s climate zones. It takes into account a variety of factors such as temperature change, changes in the length of emission seasons, different types of flux pathways, different lake and reservoir types, changes in the size of lakes and reservoirs, and nutrient levels. The results have been published in the scientific journal Nature Water.

“We find that temperature changes have by far the greatest impact on future emissions from lakes and reservoirs. Methane formation is very temperature sensitive,” says David Bastviken.

The reason is that rising temperatures speed up microbiological degradation, causing methane emissions to increase exponentially. Researchers’ calculations show that if the IPCC’s warmest climate scenario becomes a reality, current emissions of methane from lakes and reservoirs will almost double by the end of the century. This would increase total global methane emissions by about 10 percent compared to the current level, which would contribute to faster climate change than what is currently expected in the IPCC’s worst-case scenario.

Even though the situation may look sombre, it is still possible to find something positive in these results, according to David Bastviken. On the one hand, human emissions of mainly carbon dioxide are warming up the planet right now. This indirectly increases the emissions of methane from natural processes, which risks increasing the greenhouse effect even more. On the other hand, reducing human carbon dioxide emissions can have an equally clear opposite effect.

“Any reduction of greenhouse gas emissions from society has a doubling effect. It will prevent the direct warming impact of the emission, and it will also stop a corresponding future increase in methane emissions from lakes and reservoirs,” says David Bastviken.

The research was funded by the European Research Council, the Swedish Research Council, Formas and NASA’s Interdisciplinary Research in Earth Science (IDS) Program and the NASA Terrestrial Ecology and Tropospheric Composition Programs.