What exactly is permafrost?
Like glue, permafrost doesn’t melt. Instead, it thaws because it contains ground material mixed with ice.
For at least 2 years, permafrost is permanently frozen at 0°C or colder
What are the layers of permafrost?
The top 1 to 15 centimeters of permafrost is the “active layer”. During the summer, this layer thaws. Then in the winter, it freezes again. Even though permafrost is frozen, it doesn’t necessarily mean it’s covered with snow.
Below the active layer, it’s the permafrost layer. As mentioned, this is mostly ice mixed with soils, rocks, and sand. In general, permafrost ranges from 1 to 1000 meters in depth.
Why do engineers consider permafrost melt?
As ice-rich permafrost thaws, the ground settles proportional to how much ice there is in the ground. When building any type of structure, engineers have to consider heaving from permafrost.
For example, the heat used to warm the interior of a building thaws the permafrost beneath. Eventually, the structure begins to cave into the sinking ground without proper design.
- 85% of Alaska is beneath permafrost where the roads are melting from degradation.
- 30% of Yellowknife, Canada sits on Permafrost and has seen ground subsidence on average sink 1-6 cm.
How much permafrost is there?
Permafrost covers about 1/5 of Earth. It’s a prominent feature in the northern landscape that holds most of it together.
In fact, permafrost occupies over 22.8 million square kilometers in the northern hemisphere. This accounts for about 1/4 of its total area.
As you go from north to south, permafrost decreases in thickness. This is due to temperature variation from the northern latitudes.
In this flyover video, you can see how this continuously frozen layer of soil under the Arctic region is thawing.
Does permafrost melt release methane?
Permafrost is loaded with methane. Currently, there are only about 5 gigatons of methane in the atmosphere. But the amount of methane in the Arctic is in the hundreds of gigatons.
As Earth warms up, this has the potential to unlock methane from permafrost as a positive feedback loop. And methane is 25 times better at trapping heat than carbon dioxide
For permafrost, what happens in the north doesn’t stay in the north. This means there could be big changes for the rest of the world as well.
The discovery of permafrost traces all the way back to 1577 when Sir Martin Frobisher reported finding this permanently frozen ground in the far north of his journeys. But little attention was paid until the Russians described their engineering problems building on it.
The US Department of the Interior and the US Geological Survey (USGS) provide an excellent overview of permafrost. This includes “what permafrost is” and some of the environmental issues surrounding it. Despite that it’s over 25 years old now, this report on permafrost is still very relevant, today.