Arctic rain - yet another positive feedback

Earlier Arctic Rain Is Leading to 'Methane Emissions Going Bonkers'

By Tim Radford

EcoWatch,

18 February, 2019

As the global temperature steadily rises, it ensures that levels of one of the most potent greenhouse gases are increasing in a way new to science: the planet will have to reckon with more methane than expected.

Researchers who monitored one bog for three years in the Alaskan permafrost have identified yet another instance of what engineers call positive feedback. 

They found that global warming meant earlier springs and with that, earlier spring rains.

And as a consequence, the influx of warm water on what had previously been frozen ground triggered a biological frenzy that sent methane emissions soaring.

One stretch of wetland in a forest of black spruce in the Alaskan interior stepped up its emissions of natural gas (another name for methane) by 30 percent. Methane is a greenhouse gas at least 30 times more potent than carbon dioxide.

As a consequence, climate scientists may have to return yet again to the vexed question of the carbon budget, in their calculations of how fast the world will warm as humans burn more fossil fuels, to set up ever more rapid global warming and climate change, which will in turn accelerate the thawing of the permafrost.

The evidence so far comes from a detailed study of water, energy and carbon traffic from just one wetland. But other teams of scientists have repeatedly expressed concern about the integrity of the northern hemisphere permafrost and the vast stores of carbon preserved in the frozen soils, beneath the shallow layer that comes to life with each Arctic spring.

"We saw the plants going crazy and methane emissions going bonkers," said Rebecca Neumann, an environmental engineer at the University of Washington in Seattle, who led the study. "2016 had above average rainfall, but so did 2014. So what was different about this year?"

What mattered was when the rain fell: it fell earlier, when the ground was still colder than the air. The warmer water saturated the frozen forest, flowed into the bog, and created a local permafrost thaw in anoxic conditions: the subterranean microbial communities responded by converting the once-frozen organic matter into a highly effective greenhouse gas.

Alarm Rises

"It'd be the bottom of the barrel in terms of energy production for them," Neumann said. "The microbes in this bog on some level are like 'Oh man, we're stuck making methane because that's all this bog is allowing us to do'."

As global average temperature levels creep up, so does alarm about the state of the vast tracts of permafrost, home to huge stores of frozen carbon in the form of semi-decayed plant material that could be released into the atmosphere to fuel further global warming, with devastating consequences.

Spring has been arriving earlier everywhere in the northern hemisphere, including the Arctic, with unpredictable impacts on high latitude ecosystems.

The permafrost itself has been identified as a vulnerable region, change in which could tip the planet into a new and unpredictable climate regime, and geographers only this year have started to assess the direct hazard to the communities that live in the high latitudes as once-solid ground turns to slush under their feet.

More Evaporation

Much more difficult to assess is how the steady attrition of the permafrost plays out in terms of the traffic of carbon between rocks, ocean, atmosphere and living things: researchers are still teasing out the roles of all the agencies at work, including subterranean microbes.

In a warmer world, evaporation will increase. Warmer air has a greater capacity for water vapor. In the end, it means more rain will fall. If it falls in spring or early summer, the research from one marshland in Alaska seems to suggest, more methane will escape into the atmosphere.

Right now, the rewards of the study are academic. They throw just a little more light on the subtle machinery of weather and climate. The test is whether what happens in one instance is likely to happen in other, similar terrain around the high latitudes.

"The ability of rain to transport thermal energy into soils has been under-appreciated," Neumann said. "Our study shows that by affecting soil temperature and methane emissions, rain can increase the ability of thawing permafrost to warm the climate."