In the Arctic, one of the factors driving climate warming is the release of methane from permafrost and metastable gas hydrates in the shelf zone. Since researchers began to monitor temperatures in the Arctic, the region has seen two periods of abrupt warming: first in the 1920s and ’30s, and then beginning in 1980 and continuing to this day.
Leopold Lobkovsky, who authored the study reported in this story, is a member of the Russian Academy of Sciences and the head of the Moscow Institute of Physics and Technology Laboratory for Geophysical Research of the Arctic and Continental Margins of the World Ocean. In his paper, the scientist hypothesized that the unexplained abrupt temperature changes could have been triggered by geodynamic factors. Specifically, he pointed to a series of great earthquakes in the Aleutian Arc, which is the closest seismically active area to the Arctic.
Can you start off with some background? How much is the Arctic warming and how does the current temperature variation (1980-present) compare with the previous one (1920-1940)?
In brief, the ideological background of this paper is as follows. It is well known that the subsoil of the Arctic region contains large quantities of hydrocarbons, mainly natural gas. At the same time, in addition to the huge natural gas reserves in the form of large deposits located at great depths (1500-4500 m), much larger volumes of gas are located at shallow depths (several hundred meters), as well as in the near-surface layers of frozen rocks, mainly in the form of methane gas hydrates.
According to expert estimates, intrapermafrost accumulations of free gas and gas hydrates at small depths exceed by far the total reserves of conventional gas deposits. Therefore, even a relatively small fraction of the total emission of this near-surface greenhouse gas, methane, into the atmosphere can lead to a significant climate warming effect.This raises the question of the mechanisms leading to methane emission into the atmosphere and, consequently, to climate warming.
One of the possible mechanisms of such emission is the proposed seismogenic-trigger mechanism of methane release from the hydrate-containing frozen rocks due to additional stresses and deformations occurring in the Arctic lithosphere during the passage of large-scale tectonic waves excited by the strongest earthquakes in the Aleutian Island Arc.
As for the observed changes in the mean Arctic temperature during the 20th and 21st centuries, two phases of fairly abrupt climate warming are noteworthy: the first phase began approximately in 1920 and lasted about 20 years, after that the mean ambient temperature stopped rising; the second phase began around 1980 and continues to the present.
In our model we relate these phases of climate warming to periods of increased methane emission resulting from the above-mentioned seismogenic-trigger mechanism. The differences in the course of warming in the first and second phases appear to be related to the fact that during the development of the second warming phase (starting from 1980), the positive feedback of the climate system was effectively activated due to a significant decrease in the Arctic ice cover, especially from the second half of the 2000s, which led to a reduction in the albedo of the Arctic region with respect to solar radiation and, consequently, to its additional heating.
The seismogenic-trigger mechanism thus triggered an increase in methane emission and climate warming in the Arctic in 1980, and 20-30 years later another climate system mechanism was triggered by a decrease in the Arctic ice cover, which bolstered a further increase in Arctic temperatures.
What are some of the effects this rapid warming has on the local environment?
The consequences of Arctic warming are many. These include progressive melting of the permafrost, the aforementioned reduction in ice cover, changes in soil conditions, etc.
What are some of the explanations that have been proposed to explain the phenomenon and why did you find them inadequate?
Several well-developed mathematical models have been proposed to explain the general warming of the present climate, including anthropogenic emissions of carbon dioxide into the atmosphere. However, they have not provided an explanation for the observed warming episodes at particular points in time (1920 and 1980). The need to explain dramatic climate change around particular dates has stimulated an examination and analysis of large scale catastrophic natural events with the potential to cause abrupt changes in the climate system. It turned out that the strongest earthquakes occurring in the Aleutian Island Arc were best suited for this role.
What happens when there is an major earthquake hits a region like the Aleutian Arc and what prompted you to hypothesize that they were responsible for the rapid warming of the Arctic?
When a major earthquake occurs in a subduction zone with a magnitude greater than 8, particularly in the Aleutian Island Arc, a large area of contact rupture between interacting lithospheric plates occurs, representing an earthquake source that may extend for several hundred kilometres along the arc. In such an earthquake, the edge of the overhanging lithosphere shifts abruptly by several metres, disrupting the lithosphere’s state of equilibrium.
Following this removal from equilibrium the lithosphere begins to undergo relaxation oscillations resulting in large-scale deformation tectonic waves propagating at a rate of about 100 km per year. At this rate, the waves travel the distance from the Aleutian Island Arc to the Arctic shelf and adjacent land areas of about 2000 km in approximately 20 years. Upon reaching the Arctic zone, they destroy the internal structure of frozen rocks containing metastable gas hydrates which leads to the emission of greenhouse methane into the atmosphere and climate warming. Therefore, according to the model, there should be a time lag of 20 years between the onset of the strongest earthquakes in the Aleutian Arc and the onset of phases of drastic climate warming.
The history of the strongest earthquakes in the Aleutian Arc with magnitudes greater than 8 in the 20th and 21st centuries shows that there have been two series of such earthquakes during this period (early and mid-20th century) that clearly correlate with two climate warming phases in 1920 and 1980, with a 20-year shift, which is a strong argument in favour of the suggested hypothesis.
How did you go about testing your hypothesis?
The hypothesis was tested by coincidence of the phases of drastic climate warming (1920 and 1980) with the arrival of tectonic waves in the Arctic Zone 20 years after a series of the strongest earthquakes in the Aleutian Arc (series 1: one earthquake in 1899 and two in 1906; series 2: the 1957, 1964, and 1965 earthquakes). A mathematical model of such waves confirms their basic characteristics necessary for the possibility of the trigger effect, such as wave velocity, magnitude of additional stresses and deformations in the lithosphere, etc. The existence of such waves needs to be further confirmed with a whole set of factual data.
What did you discover?
The postulated seismogenic-trigger mechanism of methane emission activation is of a universal nature and is confirmed, for example, by the established confinement of methane emissions on the Arctic shelf to the sites of hypocentres of submarine earthquakes in the Laptev Sea, etc.
According to one of your charts, the first earthquake series in the region occurred in 1899, followed by two more quakes. This led to a rapid temperature change around 1920. The second series of earthquakes started in 1957, followed by quakes in 1964 and 1965. The rapid temperature rise associated with these events began around 1980. Is there a reason for the roughly 20 year lag?
As noted above, the reason for the 20-year lag between the Arctic climate warming phases and the series of large earthquakes in the Aleutian Arc is related to the arrival time of the tectonic waves generated here in the Arctic shelf region, which is about 2000 km away from the Aleutian Arc, given that the wave velocity is about 100 km/year.
The first rapid increase peaked within two decades. The current one has been ongoing for at least 30 years. Is there a reason why it hasn’t subsided yet?
As mentioned above, Phase 2 of climate warming, which began in 1980, is still ongoing, probably because another climate system mechanism has been triggered by the shrinking of in Arctic ice cover, which became evident in the second half of the 2000s, leading to a decrease in the solar reflectivity of the Arctic region and thus to additional heating of the environment.
If we extend your findings a bit, what are the environmental implications of your research?
The proposed seismogenic-trigger mechanism for the climate impact of the strongest earthquakes and associated tectonic waves opens up new avenues of research into environmental consequences of these catastrophic events, such as possible destruction of glaciers, increased volcanic activity, etc.
Finally, what is next for you in terms of research?
First of all, further work on the proposed hypothesis is needed, both in terms of a deeper physical and mathematical analysis and in terms of its verification and validation on the basis of evidence.
IMAGE CREDIT: Moscow Institute of Physics and Technology.