Letter from Alan Emery:
One of the definitions of tipping points in climate change/global warming is when a previous carbon sink shifts gears and becomes a carbon emitter. The Arctic has been a carbon sink, but according to this study [read source… ] the shift to a carbon emitter due to increasing temperatures occurred in 2012/2014. This is an increase in CO2 emissions of about 73% since 1975. That amounts to a double hit, because the CO2 is not only not being absorbed but it is now being added to by ancient carbon.
Some popular interpretations of the paper: https://www.washingtonpost.com/news/energy-environment/wp/2017/05/08/alaskas-tundra-is-filling-the-atmosphere-with-carbon-dioxide-worsening-climate-change/?utm_term=.ffe0d30d3b0a
The permafrost in the tundra has about twice the carbon that is contained currently in the atmosphere, so that could essentially multiply the atmospheric concentration by a factor of three if my arithmetic is correct – to about 1200ppm.
I should point out that the ocean is a major carbon sink as well. The concentration of CO2 is also rising in the ocean (measured as atmospheric partial pressure in the graph). The amount of CO2 the ocean water can absorb declines with increasing temperature and (obviously) with increasing concentrations of CO2. In the geological past, the shift of the ocean from a carbon sink to a carbon emitter was a key factor in the rapid increase in temperature. Needless to say, the increasing acidification (seen herein the graph) as well, is having nasty effects and will have even more as it rises.
A bit unnerving.