Climate change in northern climes

Two new studies could help scientists better monitor – and hopefully manage – climate change in the Earth’s northerly regions.

In the first, a 59-strong team of scientists from Canada, Russia, the US, Germany and Scandinavia highlights dramatic differences in the ways forests and peatlands regulate water loss to the atmosphere in a warming climate.

They gathered observational data from across the boreal biome and, writing in journal Nature Climate Change, suggest that water loss in key regions could both accelerate global warming and worsen wildfires.

Manuel Helbig from Canada’s McMaster University, who led the study with colleague Mike Waddington, says most current climate models assume the biome is all forest, an omission that could seriously compromise their projections.

“We need to account for the specific behaviour of peatlands if we want to understand the boreal climate, precipitation, water availability and the whole carbon cycle,” he says. 

As the climate warms, the researchers say, air gets drier and can take up more water. In response, the forest ecosystems that make up most of the world’s natural boreal regions retain more water. 

Their trees, shrubs and grasses are vascular plants that typically take up carbon dioxide and release water and oxygen through microscopic pores in their leaves. In warmer, dryer weather, however, those pores close, slowing the exchange to conserve water.

Lakes and peatlands – spongy bogs and fens – make up the remainder of the boreal landscape. Peatlands store vast amounts of water and carbon in layers of living and dead moss and serve as natural firebreaks as long as they remain wet.

Peatland mosses are not vascular plants, so as warming continues, they are more prone to drying out, the researchers say. Unlike forests, they have no active mechanism to protect themselves from losing water to the atmosphere. 

Dehydration exposes their dense carbon stores to accelerated decomposition, turning them from firebreaks into fire propagators – and bigger, more intense fires that can release vast amounts of carbon into the atmosphere, accelerating global warming.

In the second study, also published in Nature Climate Change, a team led by the University of Alaska Fairbanks, describes using satellite images to determine the amount of methane being released from northern lakes.

By using synthetic aperture radar (SAR), they were able to find a correlation between “brighter” satellite images of frozen lakes and the amount of methane they produce. 

“We found that backscatter is brighter when there are more bubbles trapped in the lake ice,” says lead author Melanie Engram. “Bubbles form an insulated blanket, so ice beneath them grows more slowly, causing a warped surface which reflects the radar signal back to the satellite.”

SAR can penetrate dry snow and doesn’t require daylight or cloud-free conditions. It is also good at imaging frozen lakes, particularly ones filled with bubbles that often form in ice when methane is present.

To confirm the SAR data, the researchers compared their images with field measurements from 48 lakes in five geographic areas in Alaska. By extrapolating those results, they can now estimate the methane production of more than 5000 Alaskan lakes.

Methane is about 30 times more powerful than carbon dioxide as a heat-trapping gas, and previous research has confirmed that vast amounts of it are being released from thermokarst lakes as the permafrost beneath them thaws.