Thawing permafrost in high-altitude mountains has been contributing to rising levels of greenhouse gasses in the atmosphere, new research suggests.
Forest-rich mountain ranges in Colorado capture and store carbon dioxide (CO²) from the atmosphere, but are now emitting more CO² than they capture annually.
This could lead to a feedback loop which would increase global warming and lead to more CO² emissions, experts warn.
This is similar to the situation found in the Arctic, where research in recent decades has shown that melting permafrost is unearthing long-frozen soil and releasing CO² reserves buried for centuries.
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The Alpine Tundra Ecosystem at the Colorado Front Range of the Rocky Mountains with elevations of 11,000 to 11,500 feet. the research was carried out at the Niwot Ridge Long Term Ecological Research site here, which has been in continuous operation for over 35 years
John Knowles, lead author of the new study in CU Boulder’s Department of Geography and a researcher at the Institute of Arctic and Alpine Research said: ‘We wondered if the same thing could be happening in alpine terrain.’
‘This study is a strong indication that that is indeed the case.’
Forests have long been considered vital carbon ‘sinks,’ sequestering more carbon than they produce and helping to mitigate global CO² levels.
As part of the Earth’s carbon cycle, trees and other vegetation absorb CO² via photosynthesis while microbes emit it back to the atmosphere via respiration, just as humans release CO² while breathing.
The Alpine Tundra Ecosystem at the Colorado Front Range of the Rocky Mountains starts between elevations of 11,000 to 11,500 feet.
Strong, frequent winds and cold temperatures limit what plants can grow there.
Melting permafrost, however, changes that process.
As previously frozen tundra soil thaws and becomes exposed for the first time in years, its nutrients become freshly available for microbes to consume.
Unlike plants, which go dormant in winter, microscopic organisms can feast all year long if environmental conditions are right.
To study this effect in alpine conditions, researchers measured the surface-to-air CO² transfer over seven consecutive years from 2008 to 2014 at the Niwot Ridge Long Term Ecological Research site in Colorado, a high-altitude research project that has been in continuous operation for over 35 years.
Samples of soil CO² were collected and radiocarbon dating was used to estimate how long the carbon had been present in the landscape. It showed that the barren, wind-scoured tundra emitted more CO² than they captured each year, and that a fraction of that CO² was relatively old during the winter, the first such finding of its kind in temperate latitudes.
The team also collected samples of soil CO² and used radiocarbon dating to estimate how long the carbon forming that CO² had been present in the landscape.
The study showed, somewhat surprisingly, that barren, wind-scoured tundra landscapes above 11,000 feet emitted more CO² than they captured each year, and that a fraction of that CO² was relatively old during the winter, the first such finding of its kind in temperate latitudes.
The findings suggest higher-than-expected year-round microbial activity, even in the absence of a deep insulating snowpack.
‘Microbes need it to be not too cold and not too dry, they need liquid water,’ said Knowles, now a researcher at the University of Arizona.
‘The surprise here is that we show winter microbial activity persisting in permafrost areas that don’t collect much insulating snowpack due to wind stripping it away.’
While the alpine tundra’s net CO2 contributions are small compared to a forest’s sequestration capability, the newly-documented effect may act as something of a counterweight, hampering atmospheric CO2 reductions from mountain ecosystems in general.
The findings will need to be factored in to future projections of global warming, Knowles said.
‘Until now, little was known about how alpine tundra behaved with regard to this balance, and especially how it could continue emitting CO2 year after year’ Knowles said.
‘But now, we have evidence that climate change or another disturbance may be liberating decades-to-centuries-old carbon from this landscape.’
The full report can be found in the journal Nature Communications,