For decades, scientists have warned that our increasing carbon output was putting us in danger from climate change. All current climate models point to a marked warming trend, but they may be missing an important factor. A new NASA-funded study highlights the potential proliferation of so-called “thermokarst lakes” in arctic environments. These bodies of water can thaw vast swaths of permafrost, releasing stored greenhouse gasses, and there might not be anything we can do about it.
About 24 percent of the exposed landmass in the northern hemisphere is covered with permafrost, and much of that permafrost has been frozen for thousands of years. It’s common for a few centimeters of frozen soil to thaw and refreeze during normal seasonal cycles, but scientists have noted a worrying trend where more and more permafrost is thawing and does not refreeze.
This is a problem because the arctic landscape is a natural reservoir of greenhouse gasses like carbon dioxide and methane. When the soil thaws, bacteria decompose organic material and release the carbon into the atmosphere. The thermokarst lakes can cause permafrost beneath them to thaw at an accelerated pace. Since water takes up less space than ice, the ground slumps as permafrost thaws. This creates a depression where meltwater and rain can collect, forming a thermokarst lake. Instead of centimeters of thawing, as much as 15 meters of permafrost below the lakes can thaw in short order.
The researchers traveled to Alaska and Siberia to examine thermokarst lakes up close. They found the rate of thawing to be so fast that the lakes bubble as they release methane into the air. Samples collected from the lakes show a substantially different chemical signature compared with methane from gradually thawing regions. Carbon dating confirms the emissions from thermokarst lakes contains older carbon, which indicates it’s from deeper underground. Once these lakes form and the underlying permafrost melts, there’s no way to refreeze it.
According to the study, the number of thermokarst lakes is expected to increase, and that could accelerate the pace of global climate change. Current models don’t take into account the kind of rapid thawing caused by thermokarst lakes, but the team suggests climate researchers begin factoring them in. Human fossil fuel emissions are still by far the largest source of greenhouse gasses, but thermokarst lakes are something to watch closely. Lake formation could peak within a few decades, and that could contribute substantial carbon to the atmosphere.