Across every continent, the biggest lakes are shrinking while many smaller ones are emerging. Artificial reservoirs are filling with water, and new ponds are appearing in lagoons formed by melting permafrost or retreating glaciers due to climate change. These shallow, swiftly changing lakes play a growing role in the global system and in the climate conversation, often contributing to greenhouse gas emissions in surprising ways.
Between 1984 and 2019, the surface area covered by lakes worldwide expanded by more than 46,000 square kilometers, an increase roughly equivalent to half of the Spanish region of Andalusia. This growth is linked to shifts in hydrological regimes and land use, with implications for both water resources and greenhouse gas emissions.
Researchers from the University of Copenhagen in Denmark and collaborating universities have produced a more precise and comprehensive map of the world’s lakes than ever before.
Using high-resolution satellite imagery combined with advanced artificial intelligence, the team mapped 3.4 million lakes and traced their evolution over the past four decades.
greenhouse gases
“There have been rapid and substantial changes in lake systems recently, affecting ecosystems, water availability, and greenhouse gas accounting. This new understanding of lake size and dynamics helps us better estimate its carbon emission potential,” explains Jing Tang, an assistant professor in the Department of Biology and a co-author of the study. Nature Communications.
Melting permafrost is producing smaller lakes, a trend that underscores how climate and landscape change alter regional hydrology and carbon fluxes. The study highlights that, despite many new tiny lakes, their collective climate impact is tied to how much organic matter they accumulate and how readily gases escape from their surfaces.
According to the researchers’ calculations, annual CO2 emissions from lakes increased by about 4.8 teragrams of carbon between 1984 and 2019, a pace comparable to the United Kingdom’s total carbon emissions in the early 2010s.
Since 1984, more numerous and smaller lakes (<1 km2) have appeared. This is particularly meaningful because these small lakes, though numerous, are responsible for a disproportionate share of greenhouse gas outputs. They account for roughly 15% of the planet’s lake area yet contribute about 25% of CO2 emissions and 37% of methane. They also drive a large portion of the net increases in CO2 and CH4 emissions from lakes during that period, approximately 45% and 59% respectively.
They accumulate more organic matter.
“Smaller lakes tend to accumulate more organic material, and because they are shallow, gases can more easily reach the surface and rise into the atmosphere. This makes them potent sources of greenhouse gases relative to their size,” notes Jing Tang.
At the same time, small lakes are highly sensitive to human activities and climate fluctuations. Their size and water chemistry can swing widely, making accurate mapping challenging. The researchers emphasize that careful measurement is essential to understanding their role in regional and global carbon cycles.
Two primary drivers explain the rise of many new lakes worldwide: climate change and human activity. More than half of the increase in lake area comes from artificial reservoirs, while the remainder arises mainly from melting glaciers and thawing permafrost.
Reference work: Nature Communications, 2022, detailed in the study on global lake dynamics.
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