How do we know that the Arctic circle's permafrost is melting as the region warms up?

The rivers are turning orange.

The melting permafrost is setting off a chemical reaction in iron & other metals, traces of which were trapped within the organic elements of the permafrost layer. That 'rust' then enters the water flow draining into the Arctic seas.

Although on a smaller scale this is also being detected in the Alps & the Pyrenees.

#ClimateChange #environment
h/t FT