Warming lakes could nearly double methane emissions by 2100

By the end of this century, methane leaking from lakes and reservoirs could be far higher than today. The increase would occur if the planet follows a high warming path, according to researchers in Sweden and at NASA in California.

The study shows that warmer waters, longer ice-free seasons, and expanding reservoirs all push more methane into the air from inland waters.

Those changes turn some of the planet’s quietest places into much stronger players in the climate system.

Methane from lakes and reservoirs

Methane is a heat-trapping gas that warms the planet. Over a few decades, it packs far more warming punch per pound than carbon dioxide, even though it breaks down faster in the atmosphere.

Recent work on the global methane budget (GMB), a tally of methane sources and sinks, shows that human activity releases enormous methane every year.

The analysis estimates that the world emits about 575 million tons of methane each year, with lakes and reservoirs supplying roughly ten percent of that total.

The work behind the new projections was led by David Bastviken, professor of environmental change at Linköping University in Sweden (LIU). His research focuses on how inland waters emit methane and how those emissions respond to a warming climate.

In lakes and reservoirs, methane forms when microbes break down dead plants and other organic matter in dark, oxygen poor mud at the bottom.

That process, known as anaerobic decomposition, naturally produces methane gas that then moves toward the water surface.

Some of that gas travels upward as bubbles that burst into the air, while some dissolves and is partly eaten by bacteria. The balance between these pathways controls how much methane actually reaches the atmosphere.

What the new model shows

The researchers used a data-driven model, a computer tool that learns patterns from measurements rather than only from theory. It was built from methane readings at 767 lakes and reservoirs across every major climate zone on Earth.

The model combined those measurements with climate simulations that project how temperatures and seasons may change this century.

The team tracked how methane flux from open water responds to changes in water temperature, ice free season length, nutrients, and water surface area.

Methane released from lakes

Across all scenarios, warmer water meant more methane leaving inland waters. Under a strong climate mitigation path, emissions from lakes and reservoirs still rise, but by less than one third by late century.

Under a very high warming path, emissions from these waters increase by up to about ninety percent, close to a doubling relative to today. 

“This study makes it even clearer that we really, really want to change the climate scenario as quickly as possible,” said Bastviken.

He warned that the future will be very uncertain if emissions keep pushing the climate along its current track.

A feedback that speeds up warming

The extra methane from lakes and reservoirs acts as a positive feedback, a change that reinforces the warming that caused it in the first place.

Warmer air heats surface waters and lengthens ice free seasons, which speeds up microbial methane production, which then adds more heat to the planet.

Methane also changes the radiative forcing, the net energy gain in Earth’s climate system, more strongly in the short term than carbon dioxide does.

Because methane lasts only about a decade in the atmosphere, cutting emissions can lower its heating influence on roughly human lifetime scales guidance. 

The new lake and reservoir estimates sit beside another worrying pattern from wetlands.

A recent modeling assessment found that global wetland methane emissions could rise by about thirty percent by late century if temperatures keep climbing.

Together, rising emissions from lakes, reservoirs, and wetlands mean that they add methane on top of human releases from fossil fuels, farming, and waste.

These natural boosts are not always captured in national climate plans that focus mainly on smokestacks, tailpipes, and livestock.

Why reservoirs matter so much

Many human built reservoirs sit in warmer regions and are expected to cover more area as societies build dams for energy, farming, and cities. In the new projections, those warmer waters tend to show the fastest percentage growth in methane.

Human built reservoirs often receive heavy nutrient runoff from farms, cities, and industry. This nutrient loading drives algal growth, which feeds the microbes that carry out methanogenesis, methane producing metabolism in oxygen poor sediments.

Many reservoirs also experience rapid water level changes and warm surface waters, which encourage methane rich bubbles to reach the air instead of dissolving. 

Earlier studies by reservoir specialists show that these systems emit millions of tons of methane each year through bubbling and diffusion combined inventory.

The new projections suggest that as more reservoirs are built and existing ones warm, their methane emissions could more than double in some regions.

That pattern is especially strong in tropical and subtropical belts, where year round warmth keeps microbial activity high.

Mitigation with a double benefit

The findings highlight how closely human choices link to natural responses. When societies burn fossil fuels and raise carbon dioxide levels, they heat the planet and also boost methane from lakes and reservoirs.

“Any reduction of greenhouse gas emissions from society has a doubling effect,” said Bastviken. He explained that cutting emissions avoids direct warming and also prevents an extra pulse of methane from lakes and reservoirs in the future.

Cutting methane from fossil gas leaks, agriculture, and waste can cool the climate more quickly than carbon dioxide cuts alone, because methane responds faster.

At the same time, strong carbon dioxide cuts limit future warming and keep methane forming microbes in lakes and reservoirs from going into overdrive.

For students and citizens, the takeaway is that climate action works in more ways than one. Reducing emissions today does more than prevent a hotter future – it also calms hidden amplifiers in the Earth system.

The study is published in the journal Nature Water.

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