The Pandora's Box in the Arctic has been opened?

 Methane is the second largest greenhouse gas after carbon dioxide. Although its absolute concentration in the atmosphere is less than 1/200 of that of carbon dioxide, its warming effect is 25 times stronger in 100 years. Since industrialization, the concentration of carbon dioxide has increased by less than 50%, while the concentration of methane has increased by about 150%. Recently, a report in the British "Guardian" reported that a new methane leak was discovered on the bottom of the Arctic Ocean, and the methane release mechanism has been triggered. But this statement has caused controversy.

About 99% of the world’s methane hydrates are formed in marine sediments on continental slopes, and the remaining 1% is related to permafrost in the high latitudes of the northern hemisphere (permafrost, at or below 0°C for at least two consecutive years) Related. In 15,000 years, sea levels have risen by about 100 meters, and land sediments frozen with methane have been exposed to warmer waters than previously on land. Generally speaking, the methane hydrates in the area around the Arctic Ocean, under the permafrost that is several hundred meters thick on the land and under the continental slope of the deep sea, will remain stable. Only the shallow continental shelf permafrost and the upper part of the continental slope will remain stable. Methane hydrate is easy to decompose.

In the past few decades, the surface temperature of the Arctic has risen by more than twice the global average temperature. This phenomenon in which the Arctic is warming significantly faster than the rest of the earth is the "Arctic Amplification" effect. The existence of this effect makes scientists particularly concerned about the changes in Arctic greenhouse gas content, and the uncertain methane hydrate naturally attracts more and more scientific research attention.

　　New methane leak point

The International Siberian Shelf Research (ISSS) project, jointly carried out by Russia and Sweden, has a history of 15 years. Its goal is to investigate the cryosphere-climate at the East Siberian Arctic Ocean Shelf, which stretches for hundreds of kilometers. -The interaction between the three carbons. In order to conduct a new round of expeditions, the Akademik Keldysh scientific research ship loaded with 60 team members set off on September 26 this year and returned on November 4th.

During this expedition, the scientific expedition team observed for the first time that in a large area of ​​the eastern Siberian continental slope (about 600 kilometers offshore), the methane frozen in the sediment has begun to be released. In the 150-kilometer-long, 10-kilometer-wide continental slope area, observations from 6 monitoring stations all showed that there were clusters of bubbles emerging from the sea floor.

　　 Somewhere at a depth of 300 meters in the Laptev Sea, the detected methane concentration is as high as 1,600 nanomoles per liter, which is 400 times higher than when the ocean and atmosphere are in equilibrium. Previously, the team found methane release points on the Arctic shelf in this area. The following year, in the shallow layers of the Laptev Sea and the East Siberian Sea, methane bubbles gushing out of pits on the sea floor.

　　The scientific research team stated that most of the released bubbles are still dissolved in water, but the concentration of sea surface methane is 4 to 8 times that of normal conditions, and this methane is being emitted into the atmosphere. Although the methane released is currently unlikely to have a major impact on the global climate, the key point is that the continental slope was originally considered a gas hydrate stabilization zone, and the methane hydrate in it has been disturbed, and the methane release process has been Was triggered and will continue. They believe that the warm ocean currents flowing into this area are most likely the cause of the imbalance of methane hydrate.

　　 They also emphasized that these are only preliminary findings. After they return from the scientific expedition, they must carefully analyze the collected data. Until their research results are officially published after peer review, we can know the specific figures of methane emissions.

　　 cause controversy

　　 After this report was issued, Frans-Jan W, an associate professor at Lund University in Sweden and the University of Oslo in Norway. Parmentier, NASA research scientist Ben Poulter, German Alfred Wegener Institute senior researcher Paul Overduin, and University of Chicago professor David Archer are all working on identifying the authenticity of media reports on climate change in the review site "Climate Feedback" (hermes outlet), expressed reservations about the views conveyed in this article.

First of all, the above experts believe that in the absence of long-term observation records, it is impossible to directly assert that the methane plume in the Arctic Ocean is increasing, because the methane on the seafloor may have been quietly released for a long or short period of time, but we have just discovered it. . In a 2014 study in Science, researchers analyzed the methane leakage records in marine sediments off the coast of Svalbard, Norway, and found that the methane has been released for at least 3000 years, and this It is the result of the normal seasonal fluctuation of 1~2℃ in seabed water temperature.

　　Secondly, the methane released by these sediments is not enough to have an impact on the atmosphere. The title "Sleeping Behemoth" exaggerates the fact.

In a previous study, researchers used a simple bubble model to describe the process of methane bubbles being transported vertically upward after they emerge from the sediments. Combined with observational data, they estimated how much methane the bubbles can transport from the ocean to the atmosphere. in. The results show that only in very shallow water layers (for example, less than 100 meters), methane is obviously released into the atmosphere.

　　 How much methane will eventually enter the atmosphere due to bubble transport depends on the initial size of the bubble, the release depth, and whether the bubble release scale is large enough to trigger a bubble plume.

　　 When the seawater is more than 100 meters deep, the rising methane bubbles will quickly dissolve in the seawater and eventually be consumed by aerobic methane oxidizing bacteria. Whether it is near Svalbard or the Laptev Sea, the depth of methane hydrate is more than 300 meters. Therefore, even if these methane hydrates are no longer stable, they are unlikely to pass through the barriers and affect the atmosphere. Methane concentration.

　　 A report published in Nature in 2017 pointed out that more than 1,000 methane leaks were found near Svalbard, covering a large area extending from 74°N to 79°N. Large-scale land-based, sea-based, and space-based monitoring methods have been deployed near Svalbard. Although there is a large area of ​​deposited methane release, it has not been found to have any significant impact on the atmosphere. In this way, we don't need to worry about the six newly discovered leaks in the Laptev Sea for the time being.

　　By studying global methane emissions and estimating its various emission sources, we can assess the trend of methane emissions. A data study on the global methane budget from 2000 to 2017 shows that methane emissions in the Arctic have not increased in the past 20 years, indicating that the methane released by sediments currently has no significant impact on the climate. The methane in the atmosphere mainly comes from agriculture, waste treatment, fossil fuels and natural wetlands.

　　 Just a week after the article was published, the Guardian revised part of the report and emphasized that the survey only gave a preliminary result. But aside from controversy, we must also understand that the Arctic is the region most severely affected by climate change, but it is also a place that has not been fully studied. Every new discovery here has value.

　　 real crisis

Because natural gas hydrate is sensitive to temperature and pressure, the long-term climate change process may trigger its decomposition. The large amount of methane released will enhance the greenhouse effect, and the increase in temperature will cause more permafrost to melt and release more Methane. This positive feedback process, which is difficult to stop once started, is called the flammable ice jet hypothesis (clathrate gun hypothesis), which was originally intended to explain the rapid growth of the earth during the Quaternary (about 2.6 million years ago). Temperature phenomenon.

However, this palaeoclimate interpretation linking climate warming and hydrate instability is still controversial, and whether it is in the past or in the future, it will take at least several hundred years for the global methane to be released from hydrates. time. Therefore, we should not only worry about the distant future, but also pay attention to how to solve some urgent needs.

In September of this year, a study in "Nature Climate Change" warned that the rapidly warming Arctic has begun to change from a frozen state to a completely different climate state, and the inter-annual climate change has exceeded the fluctuation range of the historical period. Scientists have found that sea ice during the coldest period in the Arctic in recent decades is less than that in the summer of the 20th century. And due to the significant increase in temperature in autumn and winter, by the middle of this century, there may be months of rain in the Arctic instead of snow.

　　 In fact, other positive feedback processes similar to the combustible ice hypothesis are indeed taking place. For example, when the temperature rises, the melting of Arctic sea ice and land ice caps will intensify, resulting in a decrease in the surface albedo and more solar radiation being absorbed, which will further increase the temperature. In addition, higher temperatures will shorten the time that carbon stays in the soil, release a large amount of carbon, and enhance the greenhouse effect. You know, the carbon content in the global soil is 2 to 3 times that in the atmosphere.

A recent study by "Nature Communications" showed that a global warming of 2°C (that is, the warming limit established by the Paris Agreement) will cause the global soil to release about 230 billion tons of carbon, which is approximately the last 100 years. my country's total carbon emissions are 4 times. If the carbon loss in permafrost is included, the estimated value will be even greater.

　　 A study on "Science Reports" pointed out that if natural methane sources continue to expand, the concentration of methane in the atmosphere will rise by 42% by 2100. In comparison, the positive impact of anthropogenic emissions reduction is much greater, and may reduce the amount of methane in the atmosphere by half in 80 years. Therefore, instead of imagining a marine monster, it is better to reduce the greenhouse gases produced by human activities through modern technology. This is what we should and can do.