by Zina Deretsky, NSF
SCIENCE: The Great Arctic Gas Leak
[Via AAAS News]
Ancient permafrost submerged in the Arctic Ocean is releasing methane gas into the atmosphere at rates comparable to previous estimates for all the world’s oceans combined, researchers say. This underwater permafrost represents a large but previously overlooked source of methane, and experts say that similar but more widespread emissions of the gas could have dramatic effects on global warming in the future.
The discovery creates “an urgent need” for further research to understand the methane release and its possible impact, researchers say in the new issue of Science.
[More]
This is not good news.
There are a couple of very worrisome reports that have come out recently looking at methane emissions. The first one deals with methane production, which I have mentioned before. Remember, methane dissolved in ocean water degrades to CO2, lowering the pH of the oceans and making it harder for them to take up atmospheric CO2 but also meaning that less methane actually makes it to the surface to be transferred to the atmosphere. This paper describes a process where methane is able to be directly transferred, resulting in increasing atmospheric methane levels.
And remember that over a twenty year period, methane is about 70 times a more potent greenhouse gas than CO2.
The release of methane from natural sources, such as the oceans and wetlands represent only perhaps 25% of all methane emissions. Most of the rest is due to totally human-caused reasons. These include livestock emissions, rice paddies, and fossil fuels. These are all things that have only produced such high levels of methane in the last hundred years. The natural methane cycle probably emits about 150 teragrams of methane per year.
But the new paper in Science – Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf – demonstrates that the release of methane from Arctic permafrost sources is much higher than previously believed. The waters of the East Siberian Arctic Shelf are supersaturated with methane at all depths. This methane is being released from undersea deposits because the previously impermeable permafrost layer is degrading, due to increased temperatures in the Arctic. Previous to the warming, the methane was trapped beneath the permafrost. Now, it is being released.
And because this column of water here is so shallow (average depth is 45 m) most of the methane is not oxidized to carbon dioxide, as seen in the open oceans, but is directly vented to the atmosphere as methane.
This means that much more of the methane makes it into the atmosphere than regions closer to the Equator. Most likely over 8 teragrams of methane is outgassed a year. This is an example of positive feedback loops due to warming. A warmer Arctic releases more methane, which makes the climate warmer, releasing more methane.
This is almost as much as had been previously attributed to the entire global emission of methane from clathrates. More than previously expected from just one area in the Arctic.
The other paper – Large-Scale Controls of Methanogenesis Inferred from Methane and Gravity Spaceborne Data – examined the increase in methane emissions from another source – wetlands. Using satellites, they were able to measure the increase in methane emissions since 2003. They found that globally, the amount of methane entering the atmosphere from wetlands has been increasing each year. In 2003, the total of methane being emitted by wetlands was about 170 teragrams a year and had been flat for many years.
By 2007, the amount of methane being emitted globally had increased by about 10 teragrams a year:
So, in less than 4 years, the amount of methane being added to the atmosphere every year by wetlands had increased 6%. And again, almost all of this increase appears to be due to a warming climate.
These two papers show that there are much greater amounts of methane being produced each year because of a warming climate. This just adds to the tremendous increase in methane levels over the last 150 years or so.
Here is a graph of the increase of methane in the atmosphere during historical times, comparing ice cores from Antarctica and Greenland:
Over the last 400,000 years, methane has varied from about 350 parts per billion (ppb) to 700 (green line).
We are now at about 1788 ppb, more than double any amount over the last 400,000 years Actually, it is double what it was in the 1750s. After an almost decade long lull with little increase in atmospheric methane, we are beginning to see increases again. In fact, there has been a substantial increase in atmospheric methane levels since 2006, paralleling the amounts that these two papers suggest have been emitted. This is particularly disturbing because of what has happened in the past due to possible methane emissions.
The largest mass extinction in the planet’s history may have been due to a rapid releases of huge amounts of previously buried methane. The Permian-Triassic extinction happened 250 million years ago, resulting in the extinction of 96% of all marine species and 70% of land animals. It is the only extinction event that actually had a huge effect on insect populations. TMethane emissions appear to be the most likely culprit. That is because it is easy to tell when large amounts of organically-derived methane is released. There was a rapid change in the atmospheric ratios of carbon isotopes.
Only methane presents an avenue for so much organically-derived carbon to have been released so rapidly.
Again, the greatest excursion of temperatures in the current Era, the Paleocene-Eocene Thermal Maximum, happened 55 million years ago and also appears to have seen accompanied by large releases of methane.
Both of the events took place very rapidly in a geologic sense. Perhaps in less than 1000 years. Well, we are about 200 years along that time line.
Methane release can be the one thing that shifts us to a different climate regime, one that may well be irreversible, no matter how much we reduce carbon dioxide levels.
