7 January 2016 (Stockholm University) – Climate-sensitive regions in the north are home to most of the world’s lakes. New research from universities in Sweden and the US, shows that these northern freshwaters are critical emitters of methane, a more effective greenhouse gas than carbon dioxide.
Methane is increasing in the atmosphere, but many sources are poorly understood. Lakes at high northern latitudes are such a source. However, this may change with a new study published in Nature Geoscience. By compiling previously reported measurements made at a total of 733 northern water bodies – from small ponds formed by beavers to large lakes formed by permafrost thaw or ice-sheets – researchers are able to more accurately estimate emissions over large scales.
“The release of methane from northern lakes and ponds needs to be taken seriously. These waters are significant, contemporary sources because they cover large parts of the landscape. They are also likely to emit even more methane in the future”, says Martin Wik, PhD student at the Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm University, who led the study.
With climate warming, particularly at high northern latitudes, longer ice-free seasons in combination with permafrost thaw is likely to fuel methane release from lakes, potentially causing their emissions to increase 20–50 precent before the end of this century. Such a change would likely generate a positive feedback on future warming, causing emissions to increase even further.
“This means that efforts to reduce human induced warming are even more urgent in order to minimize this type of feedback of natural greenhouse gas emissions. In a sense, every reduction in emissions from fossil fuels is a double victory”, says David Bastviken, Professor at Tema Environmental Change, Linköping University.
About the study
Climate-sensitive northern lakes and ponds are critical components of methane release is published in Nature Geoscience. The study was a joint effort between members of the Permafrost Carbon Network: Martin Wik, Ruth Varner (Associate Professor, University of New Hampshire), David Bastviken, Katey Walter Anthony (Associate professor, University of Alaska Fairbanks), and Sally MacIntyre (Professor, University of California, Santa Barbara). It was funded by the National Science Foundation and the Swedish Research Council.
ABSTRACT: Lakes and ponds represent one of the largest natural sources of the greenhouse gas methane. By surface area, almost half of these waters are located in the boreal region and northwards. A synthesis of measurements of methane emissions from 733 lakes and ponds north of ~50° N, combined with new inventories of inland waters, reveals that emissions from these high latitudes amount to around 16.5 Tg CH4 yr−1 (12.4 Tg CH4-C yr−1). This estimate — from lakes and ponds alone — is equivalent to roughly two-thirds of the inverse model calculation of all natural methane sources in the region. Thermokarst water bodies have received attention for their high emission rates, but we find that post-glacial lakes are a larger regional source due to their larger areal extent. Water body depth, sediment type and ecoclimatic region are also important in explaining variation in methane fluxes. Depending on whether warming and permafrost thaw cause expansion or contraction of lake and pond areal coverage, we estimate that annual water body emissions will increase by 20–54% before the end of the century if ice-free seasons are extended by 20 days. We conclude that lakes and ponds are a dominant methane source at high northern latitudes.