The high cliffs of Eastern Siberia – which mainly consist of permafrost – continue to erode at an ever quickening pace. This is the conclusion which scientists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research have reached after their evaluation of data and aerial photographs of the coastal regions for the last 40 years.
According to the researchers, the reasons for this increasing erosion are rising summer temperatures in the Russian permafrost regions as well the retreat of the Arctic sea ice. This coastal protection recedes more and more on an annual basis. As a result, waves undermine the shores. At the same time, the land surface begins to sink. The small island of Muostakh east of the Lena Delta is especially affected by these changes. Experts fear that it might even disappear altogether should the loss of land continue.
This represents another feedback. Along the very long coasts, permafrost doesn't have to melt slowly from the top down. It's calving into the sea, similar to what glaciers do. Since these are very shallow coastal waters, nearly all the carbon in that permafrost would go straight into the atmosphere. And the longer the seas stay ice free near the coast every year, and the more of the sea is open, the more erosion there will be just from the mechanical action of the larger waves, let alone the melting effect of ever-warmer waters and air.
If the average temperature rises by 1 degree Celsius in the summer, erosion accelerates by 1.2 metres annually...
During the past two decades, there were, on average, fewer than 80 ice-free days in this region per year. During the past three years, however, we counted 96 ice-free days on average. Thus, the waves can nibble at the permafrost coasts for approximately two more weeks each year...
During the past 40 years, the coastal areas surveyed retreated on average 2.2 meters per year.
“During the past four years, this value has increased at least 1.6 times, in certain instances up to 2.4 times to reach 5.3 meters per year“...
OK, start with 5 meters per year and start doubling it every four years for the next 40 years and what do you get, you math geniuses out there?
And what does the rate get to after the next 40 years?
What is the total number of square meters would of permafrost land surface that will have dropped into the sea by then (and thence into the atmosphere)?
How much carbon will that represent?
Will the rate of acceleration increase or decrease as the sea gets ever warmer and wilder?
I can't imagine that the rate will stop increasing at least until there is no sea ice close to that part of the coast year round.
Is there anything that is likely to stop or even slow (or even slow the rate of increase of) this process?
ETA: As the first commenter on the site linked pointed out, similar rates of coastal erosion are being reported in Alaska. It must be assumed that such rates are typical around much of the Arctic Ocean. So put that into your equations and smoke it.