Ice and Fire: The role of methane in the climate story

By a biogeochemist who studied the molecule

What I study

Two years ago, I partook in a scientific conference of early career arctic climate scientists and paleolimnologists (the study of lake records to illuminate past environmental conditions). The ice breaker (no pun intended) consisted of us writing a 200-or-fewer synopsis on our work, using only the 1,000 most common English words (see: https://xkcd.com/simplewriter/). The idea of using this editor is that the simpler the words we use to describe our work, the easier it would be to understand. Here was my entry:

In a world where the sun burns hotter and the waves and winds start to die, our world begins to lose a lot of very old ice that was locked far far away in the high north circles of the Earth. As this ice becomes water, it puts into the air lots of little things called “air fire” which force the world to be even hotter than it already was. With no countering forces, the Earth starts to run away with green houses… It is up to me to save the world. What I do to fix the running away of green houses is to study how little water grasses within water bodies can add or remove this “air fire.” If we can understand how this works, then we can try to stop our Earth from warming up too much. This way, future babies won’t cry, we will have good food and stuff for a long time and things will be great.

Aside from the Trump-speak towards the end, this serves as a pretty good condensed abstract of my master’s thesis.

In modern parlance,

I studied the impact of submerged vegetation abundance on methane dynamics in the context of a discontinuous permafrost peatland lake system, in Abisko, Sweden, north of the Arctic Circle.

Carbon dioxide (CO2)

CO2, methane’s more popular greenhouse gas cousin, receives the most attention. Although CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions, the ocean has served as a sink, absorbing about 30% of the emitted anthropogenic CO2, (at the expense of ocean acidification)[1]. Thus, CO2 is important to the climate story— and it has a large anthropogenic signature — but methane is relatively underrepresented.

Methane (CH4)

Methane, the “air fire” mentioned above, is the third most abundant greenhouse gas, and although it is more short-lived in the atmosphere than CO2 (~8 years vs. ~100 years), it has ~30 times greater global warming potential over a 100-year life time[2]. This means that although CH4 has a shorter residence time in the atmosphere, it is still 30x more potent a greenhouse gas. As such, fluctuations of CH4 emissions affect the Earth’s radiation budget more strongly in shorter timescales than does CO2.

The environmental concentration of CH4 has increased by a factor of 2.5 since preindustrial times, from 722 ppb in 1750 to 1803 ppb in 2011, which is believed, with very high confidence, to be caused by anthropogenic activities (increase in ruminants, fossil fuel extraction and use, expansion of rice paddy agriculture, and the emissions from landfills and waste). Current anthropogenic emissions account for 50 to 65% of total emissions.

In recent decades, CH4 growth in the atmosphere has been variable, with large uncertainty as to the main drivers, leading to a lot of scientific inquiry to elucidate the factors at play. CH4 concentrations were relatively stable for about a decade in the 1990s, but then started a period of regrowth in 2007. The interannual variability of CH4 emissions is believed to be due to climate-driven fluctuations of CH4 emissions from natural wetlands, with a smaller but significant contribution from biomass burning emissions during high fire years.

The importance of fire to the climate story

Contained in vast circumpolar zones of permafrost, or frozen soil, is about 50% of the global soil carbon store [3]. Fire frequency and severity have been observed to be increasing in the boreal permafrost zone [4], and rare stochastic events such as the large Alaskan tundra wildfire in 2007, have exhibited unprecedented carbon loss [5]. This was a poignant event for climate scientists, as it taught us that singular fire events can lead to huge carbon loss in the form of CH4 and CO2, in very short timescales, in an ecosystem where fire has not historically been a factor.

The hypothesis: As northern, permafrost zones thaw, they drain of their water, making the fuel-rich landscape dry and amenable to fire, potentially admitting a world of fire into the land of ice.