Methane emissions from Arctic soils are on the rise

Photo by  Annie Spratt

Photo by Annie Spratt

Article III: Explain another potentially more severe consequence of Arctic warming.

Microbial respiration of previously frozen carbon is releasing carbon dioxide (CO2) into the atmosphere (Cory, R., et al.), but that is not the only gas that is being released. Microbial decomposition also leads to the release of methane (CH4) from this dissolved carbon. In the last article we talked about carbon dioxide emissions from Arctic permafrost, but one study revealed that methane emissions since the 1950s have been proportional to permafrost carbon thawed in Arctic lakes (Anthony, K. W., et al.).

When a thermokarst failure occurs, this provides a direct pathway for the newly released carbon to be processed and released into the atmosphere. The hollows, known as thermokarst lakes, are simply thermokarst failures that fill with melt water in the depression created by the soil collapsing. These lakes are estimated to have been forming in the Arctic during the entirety of the Holocene epoch and measurements can therefore be made dating back approximately 11,700 years.

At the bottom of these lakes, taliks forms. A talik is simply an anaerobic thaw bulb – or bubble – at the bottom of the lake that is not in contact with the atmosphere (Anthony, K. W., et al.). In these bubbles, carbon undergoes degradation and anaerobic simply means that no free oxygen is available in this process. This means that the CH4 produced from this degradation does not dissolve well into the surrounding water. It is therefore easily released to the atmosphere as these bubbles rise from the bottom of the lake. These methane filled thaw bulbs are released as the Arctic is heating and the thermokarst lakes are thawing.

The temperature in the arctic is expected to rise by up to 7.5 °C by 2100 and this will cause melting is deeper and deeper parts of the permafrost and expose much older buried carbon. Due to its prior non-exposure to light, this carbon risks being converted almost completely to greenhouse gases. As temperatures keep increasing, predictions tell us that additional large emissions of CH4 could come from even deeper carbon thaw. Not only is the amount of carbon release increasing, the rate of release is also expected to accelerate (Anthony, K. W., et al.).

These CH4 emissions can be measured a modelled. The models predict that the CH4 emissions from permafrost soil carbon in thermokarst lakes will be up to 100 times faster than past rates, quantitatively this is equal to 103 up to 129 teragrams of carbon released every year (Anthony, K. W., et al.). For reference, a teragram of carbon is equal to a trillion grams, a number almost too large to comprehend.

Similar models were made for terrestrial non-lake Arctic environments. Here, the release of CH4 could become up to 900 times faster than the rate of release observed in the past sixty years and quantitatively this will entail 356 up to 930 teragrams of carbon released every year (Anthony, K. W., et al.). Without halting this melt, thawing permafrost risks becoming one of the main drivers of future climate change and could have dire consequences for life on our planet.

Methane is a really potent greenhouse gas, much more powerful than CO2. It is considered to be about 30 times more effective than CO2at scattering the radiation in our atmosphere and preventing this heat from escaping. If all this carbon was to be released as methane, global climate change could accelerate to significantly more dangerous levels.


REFERENCES

  • Cory, R., Crump, B., Dobkowski, J. and Kling, G. (2013). Surface exposure to sunlight stimulates CO2 release from permafrost soil carbon in the Arctic. Proceedings of the National Academy of Sciences, 110(9), pp.3429-3434.

  • Walter Anthony, K., Daanen, R., Anthony, P., Schneider von Deimling, T., Ping, C., Chanton, J. and Grosse, G. (2016). Methane emissions proportional to permafrost carbon thawed in Arctic lakes since the 1950s. Nature Geoscience, 9(9), pp.679-682.

Hannah Rane