The Siberian carbon bomb
We rightfully focus on carbon emissions from human activity as a primary driver of climate change and global warming. But in our visions of the future, we need to also account for the increasing role Mother Earth plays in heating our atmosphere and oceans. Beyond the fringes of civilization, a carbon bomb is ticking in the Arctic wilderness. This bomb is now set to explode. Initially driven by fossil fuel emissions, global heating has become the catalyst for opening natural pathways for the release of massive quantities of carbon-based greenhouse gases.
Extreme summer heatwaves during the past several years pushed temperatures in Siberia to record highs. Dangerously high temperatures extended northward into the Arctic Circle, triggering a variety of natural carbon-release processes and pumping carbon dioxide and methane into the atmosphere.
This natural release of carbon may eventually become self-sustaining. Summer heat causes the release of significant amounts of greenhouse gases. These added gases exacerbate global heating, leading to even warmer summers in the future. The point at which this feedback loop becomes self-sustaining is called the tipping point. After reaching the tipping point, human efforts to control fossil fuel emissions become secondary. The world will continue heating from Arctic carbon regardless of whether we lower fossil fuel use.
The primary pathways for natural carbon release in the Arctic include:
- The microbial decay of organic material.
- Thawing of methane hydrates (clathrates).
- The release of hydrocarbons from below the permafrost.
Methane gas collects below the frozen surface of the Arctic. A thick layer of frozen permafrost possesses structural integrity, just like ice on a lake. Air bubbles can collect below the lake ice, but they won’t normally break through. However, if the ice over the bubble thins enough, then the buoyancy force of the air may be enough to burst through the ice.
Air doesn’t collect below the permafrost, but methane does, and western Siberia contains some of the largest shallow-methane deposits in the world. The methane can exist in a gaseous or solid state, depending on temperature and pressure conditions. Solid deposits of icy methane are called hydrates or clathrates.
Summer heatwaves naturally thaw the permafrost, and as it loses structural integrity, the methane below releases into the atmosphere. Under the right conditions, methane gas catastrophically explodes from below creating enormous craters, which pockmark the Siberian landscape.
These mysterious craters are appearing more frequently as our planet warms. But methane release need not be explosive. Slow, steady leakage through the melting permafrost is more often the case. Methane seeps bubbling through Arctic lakes are not uncommon.
Researchers working in Siberia recently uncovered evidence of methane emanating from two large outcrops of ancient Paleozoic carbonates, which cover thousands of square kilometers. Carbonates are common reservoir rocks for hydrocarbons. However, these Siberian carbonates are not deep underground but at the Earth’s surface, covered only by frozen rock and soil. As the carbonate rocks warm, cracks form, allowing trapped methane and other hydrocarbons to seep into the atmosphere.
The annual release of large methane deposits is worrisome because methane is a super-warmer. The effect of particular greenhouse gases on global warming is a function of two factors: warming potential and lifetime (time in the atmosphere). Methane’s lifetime is short (~12 years) compared to CO2, which lasts for centuries. But methane’s warming potential is over 80 times greater than CO2 during the first 20 years after it enters the atmosphere. Release a ton of methane into the atmosphere, and over a 20-year period, it has the warming potential of 80+ tons of CO2.
A Microbial Feast
Permafrost is not just frozen soil. Permafrost often forms over centuries and during that time, plants and animals live and die, with their remains frozen into the soil. Normally organic matter in the soil is consumed by microbial bacteria. This normal carbon cycle is interrupted when permafrost forms.
Plants and animals require carbon to live and they carry their carbon to the grave when they die. Under most circumstances, their death starts a process where bacteria break down the organic material and release carbon back into the atmosphere as carbon dioxide and methane. Permafrost creates a time capsule where decomposition is interrupted, and the carbon remains sequestered in the icy soil.
An estimated 1,400 gigatons of carbon lie frozen in the Arctic permafrost. By comparison, the Earth’s atmosphere contains only 850 gigatons of carbon. When summer’s heat thaws the Arctic, the frozen organic material becomes available to bacteria, and the feast begins. The bacteria rapidly consume the centuries-old animals and plant remains and return the carbon to the atmosphere as carbon dioxide and methane.
Then Comes the Fire
Boreal forests stretch across the high northern latitudes of Europe, Asia, and North America. These forests are major carbon sinks, sequestering carbon above-ground in biomass and below-ground in the forest soils. The boreal ecosystem also contains vast areas of peatlands.
Boreal forests exist where freezing temperatures occur for six to eight months of the year. These forests are defined by trees reaching a minimum height of five meters and the development of a forest canopy covering at least ten percent of the forest area. Mixed with stretches of boreal forests are peatlands, which are dominated by lakes, bogs, and fens. These wetlands contain thick layers of living and dead moss, thus making them excellent carbon sinks. When water is abundant and temperatures low, decay slows, helping the sequestration of carbon.
The ability of boreal ecosystems to sequester carbon is very dependent on retaining high levels of moisture within the plants and soils. The moisture deters or retards fires, keeping the carbon locked and out of the atmosphere. But heatwaves in the far north and Arctic change the normal balance by drying out the forests and peatlands.
Siberia experienced severe forest fires during the past several hot summers. A single monster fire in the Yakutia region of Russia burned 10 million acres in the fist seven months of 2021. Human activity and natural events, like lightning strikes, start these fires. But regardless of the source, as Siberia burns, large amounts of new CO2 flood into the atmosphere.
When peat or other organic-rich soils dry out, then the preserved carbon can ignite and burn. Wet peatlands within boreal forests are usually natural fire breaks. However, dry peatlands are zones of fire propagation, not fire breaks.
If conditions are dry enough, highly organic soils below a wildfire will also start burning, and the fire won’t necessarily remain at the surface. The fire makes its way underground, where it maintains a long, slow burn. Zombie fires in the boreal peatlands and forests occur when the underground fires smolder throughout the winter. As warm weather returns, these fires resurface and start new wildfires.
Anthropocene warming kicked off various natural, carbon-release processes in the northern extremes of our planet. If left unchecked, these processes will tip into self-sustaining feedback loops. We don’t know the exact timing of the tipping point, and we could have already passed it. But once we reach a point of no return, our efforts to control fossil fuel emissions become a secondary consideration. Nature will take its course, and the earth will continue to warm on its own accord until the supply of Arctic carbon is exhausted.
Related Stories by WM House:
Cows Belch Methane, So Does the Earth (by WM House; Medium)
Permafrost: A ticking carbon bomb (by WM House; ArcheanWeb)
Water loss and plant biology: The demise of boreal peatlands (By WM House, ArcheanWeb)
Wildfires and zombie fires (by WM House; ArcheanWeb)
Scientists expected thawing wetlands in Siberia’s permafrost. What they found is ‘much more dangerous.’ (By Steven Mufson; The Washington Post)
One of the Coldest Places on Earth Is on Fire (by Ann M. Simmons; The Wall Street Journal)
Feature Image — Input Imagery Credits: By Ninaras — Own work, CC BY 4.0, Wikimedia Commons; Northwest Crown Fire (Modified) — By (Photograph used by permission of the USDA Forest Service.) — Bunk S: World on Fire. PLoS Biol 2/2/2004: e54. doi:10.1371/journal.pbio.0020054.g001, CC BY 2.5, Wikimedia Commons