Across every continent, the largest lakes are shrinking while many smaller ones are appearing. Artificial reservoirs are filling, and new ponds are forming in lagoons created by melting permafrost or retreating glaciers as the climate changes. These shallow, rapidly shifting lakes are increasingly visible in our global water system and in climate discussions, and they can influence greenhouse gas emissions in surprising ways.
Between 1984 and 2019, the surface area covered by lakes worldwide grew by more than 46,000 square kilometers, a gain roughly equivalent to half of the Spanish region of Andalusia. This growth follows shifts in hydrological patterns and land use, with important implications for water resources and climate dynamics.
Researchers from the University of Copenhagen and partner institutions have produced a more precise and comprehensive map of the world’s lakes than ever before.
By combining high-resolution satellite imagery with advanced artificial intelligence, the team mapped 3.4 million lakes and tracked their changes over the last 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 improve estimates of carbon emissions from lakes.
Melting permafrost creates smaller lakes, illustrating how climate shifts and landscape changes alter regional hydrology and carbon fluxes. The study notes that even with many new tiny lakes, their overall climate impact depends on the amount of organic material they accumulate and how easily gases escape from their surfaces.
According to the researchers’ calculations, annual CO2 emissions from lakes rose 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 (less than 1 square kilometer) have appeared. This trend matters because these small lakes, while widespread, 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, roughly 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.
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.
Small lakes accumulate more organic matter and are particularly responsive to changes in land use, drainage, and warming temperatures. Their shallow depths mean that even minor shifts in temperature and hydrology can alter gas exchange rates, reinforcing the need for ongoing monitoring and robust data collection.
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.
The evolving map of the world’s lakes highlights not just winners and losers in lake area but also the complex balance between ecological health, water security, and climate feedbacks. As landscapes continue to adjust, ongoing observation and analysis will be essential to understand how these water bodies influence regional climate patterns and atmospheric chemistry over time.
Further studies will explore how different lake types contribute to regional energy balances and nutrient cycles, as well as how policy choices affect water management and greenhouse gas emissions in lakes around the world.
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