The northern cryosphere is experiencing rapid warming—up to four times faster than the global average. This phenomenon not only threatens the delicate balance of these ecosystems but also leads to the release of massive greenhouse gases (GHG). As a region with large carbon and nitrogen storage and a widespread presence of lakes and rivers, GHG emissions from cryosphere inland waters have attracted much attention among biogeochemists and the public. Alarmingly, the overall magnitude of GHGs in cryosphere inland waters is still unclear, until now.
A recent paper published in Science Advances has unveiled a significant and worrying aspect of climate change: the greenhouse gas emissions from inland waters in the northern cryosphere, which could offset the carbon absorption capabilities of terrestrial ecosystems. This highlights how lakes and rivers in these cold regions are contributing more to greenhouse gas emissions than previously understood, raising concerns about their role in climate dynamics.
The research team, led by Chunlin Song from Sichuan University in China and Jan Karlsson from Umea University, conducted a comprehensive analysis of greenhouse gas emissions from nearly 3,000 measuring sites in lakes and rivers across the northern cryosphere. Their findings reveal that these water bodies emit an estimated 1.5 to 2.3 petagrams of CO₂ equivalent (CO₂e) per year. If this magnitude is compared within the ranking of global national greenhouse gas emissions, it would be equivalent to the 6th largest emission zone in the world. This staggering figure underscores the urgent need to understand the role of inland waters in the global carbon cycle.
The study highlights a striking disparity in greenhouse gas emissions between rivers and lakes. While rivers occupy only one-fifth of the surface area of lakes, they are responsible for 64% more CO₂ equivalent emissions. This is largely attributed to their close interaction with terrestrial ecosystems, which facilitates a higher outgassing rate of carbon dioxide.
Moreover, the research indicates that the continuous permafrost zones contribute nearly half of all inland water GHG emissions. This finding is particularly alarming, as it suggests that the thawing of permafrost is releasing significant amounts of stored carbon into the atmosphere, further exacerbating climate change.
The emissions from northern cryosphere inland waters are not just concerning in isolation; they have broader implications for the global carbon budget. The study shows that annual CO₂e emissions from these waters exceed the terrestrial net ecosystem exchange in the region, meaning that the carbon sink provided by forests and other land ecosystems is being undermined by emissions from lakes and rivers.
The researchers also discovered seasonal variations in greenhouse gas emissions, with peaks in emissions occurring during the ice melt in spring and summer. This seasonal flux highlights the dynamic nature of these ecosystems and the complex interactions between land and water, emphasizing the need for ongoing research to fully understand these processes.
Importantly, the study calls attention to the current inadequacies in Earth System Models, which often overlook the contributions of inland water bodies in cryospheric regions. As climate change accelerates, these models must evolve to incorporate these vital emissions to accurately predict future climate changes.
The implications of this research are profound. As global temperatures continue to rise, the northern cryosphere's role in greenhouse gas emissions may become increasingly significant. The study serves as a wake-up call for scientists, policymakers, and the public, stressing the need to reassess our understanding of cryospheric carbon dynamics in the context of climate change. It is crucial to recognize the impact of inland waters in the northern cryosphere not only as sources of greenhouse gas emissions but also as integral components of the global carbon cycle. Addressing these emissions will be essential in our efforts to combat climate change and preserve the delicate balance of our planet's ecosystems.
More information: Chunlin Song et al., Inland water greenhouse gas emissions offset the terrestrial carbon sink in the northern cryosphere. Sci. Adv. 10, eadp0024 (2024). DOI: 10.1126/sciadv.adp0024
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