# What is the relevance of Arctic coastal erosion to the Earth's climate?

Due to global warming and Arctic amplification, Northern Hemispheric permafrost is thawing and becoming a source of carbon and many greenhouse gases, which then positively feedback to global warming again.

More specifically, severe Arctic coastal erosion of permafrost material has taken place in recent years. How relevant is this specific process, alone, to Earth's climate in general, or at least to the Arctic climate?

If we consider only the climatic impacts of Arctic coastal erosion, there are still two sides of the question of how relevant is Arctic coastal erosion of permafrost.

The first side is how big is its current role as a $${CO}_2$$ source, and the second is how much of risk it posses for future climate change.

It term of current contribution the answers is that it is not very relevant. According to the "The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines" from 2011, there are 101,447 km of coastline in the Artic, and the mean coastal erosion rate is 0.5 m/yr with a mean backshore elevation of 8.3 m. Multiplying all those numbers we get that 421,005,050 $$\text{m}^3$$ of Arctic soil are lost to the sea every year.

That paper is behind a paywall so I'll copy here Table 2 (where most of above numbers come from) and figure 6 that are relevant here.

Table 2 also indicates that ~2% of the weight of that lost soil corresponds to carbon, so using a bulk density of 1,900 $$\text{kg}/\text{m}^3$$ (source) you get that the lost corresponds to 0.00002 Pg C (peta grams of carbon) per year, a very small number compared with the ~7.8 Pg C that burning fossil fuels put into the atmosphere every year.

Now, it is more concerning the potential of permafrost lost. Scientist have studied Arctic ocean sediments and found that during the period of fast sea level rise at the end of the last ice age, a huge amount of organic carbon stored in permafrost was released (source), perhaps close to 1,000 Pg (source). Carbon that was then available for microorganism to metabolize and transform into greenhouse gases as carbon dioxide and methane. This greenhouse gases helped warming the Earth and melting the ice caps that covered it at that time.

There are still about 1,300 Pg of carbon stored in permafrost (source). Thawing of permafrost is increasing rapidly. As well as coastal erosion rates. In coastal Alaska for example it have increased from 6.8 m/yr in 1955-1979, to 8.7 m/y in 1979-2002, to 13.6 m/yr on 2002-2007 (source). Arctic warming, sea level rise and release of permafrost organic carbon form part of a dangerous positive feedback cycle that we don't know how far or how fast it can go. And it have the potential to release massive, and this time, VERY considerable quantities of greenhouse gases into the atmosphere.

• Thanks for such a nice answer! "...a dangerous positive feedback cycle that we don't know how far or how fast it can go. " -- so I understand there is potential to impact climate, but we don't know yet by how much, correct? In other words: how much will Arctic coastal erosion add to global warming? – David Nielsen Feb 20 '19 at 17:50
• @ouranos Yes there is a potential to impact climate, but consider that those large amounts of carbon stored in permafrost can't be released by coastal erosion only, that would require the thawing of permafrost inland. Costal erosion is just one of the factors involved in amplifying the mentioned and dangerous positive feedback loop (if you are satisfied with the answer remember to accept it). – Camilo Rada Feb 20 '19 at 18:00
• Clear. Now, to respond to "how relevant" Arctic coastal erosion is to climate (change), to give it a number, what would it be? How much is its influence? – David Nielsen Feb 22 '19 at 10:17
• @ouranos The 0.00002 PgC vs ~7.8 PgC/year does actually put a number to it. However, the contribution of coastal erosion to $CO_2$ emissions is just part of it. There are other pathways through which coastal erosion impacts climate, such as methane emissions, changes in albedo, or nutrient inflow to the sea. But this is just one among millions of interacting pieces. Coastal erosion leads to the loss of 51 km² every year, but then an arab sheikh decides to build an 80 km² island with a Palm tree shape... You might find this Q&A interesting: earthscience.stackexchange.com/q/16286/11908 – Camilo Rada Feb 28 '19 at 18:42

SANDIA REPORT“The Arctic Coastal Erosion Problem”by Sandia National Laboratories, SAND2016-9762, September,2016

"One-third of the coastline in the world is Arctic permafrost [Lantuit et al., 2012]. Despite this sizeable proportion, a comprehensive understanding of erosion dynamics in the Arctic has not yet emerged. Unfortunately, the majority of present knowledge regarding coastal landscape evolution is confined to areas with temperate climates and non-cohesive sediments. Oceanographic and geomorphic feedbacks in the Arctic may be complex, but the need to interrogate these processes with physics-based modeling is becoming increasingly important. This urgency is underscored by scientific work that demonstrates erosion rates for many Arctic locations are increasing."

• Please add something that shows that this report answers What is the relevance of Arctic coastal erosion to the Earth's climate? I don't see that in the report. – Jan Doggen Apr 19 '19 at 6:09
• Thanks for bringing up this nice review material on the topic. – David Nielsen May 7 '19 at 11:32