Is There a Future Tipping Point in the Atlantic Meridional Thermohaline Circulation (AMOC)?

by Emil Morhardt

The AMOC is the set of ocean currents that begins with cold seawater off Greenland sinking to the bottom and flowing south, being replaced by warmer water flowing at the surface past Florida from the south, transferring warmth from the tropics to the east cost of North America and the West Coast of Europe. The full round trip cycle from, and back to, Greenland takes a thousand years. Without it, both western Europe and eastern North America would cool significantly, with large numbers of potential adverse effects. We know from ice core record temperature data from both the Greenland Ice Sheet (GrIS) and from Antarctic ice sheets, that the AMOC has come to an abrupt halt many times, and has characteristically taken a millennium to recover. The comparative abruptness of these cessations has led to the fear that there may be some threshold that once crossed—a tipping point—that cessation is inevitable. This would be nice to avoid. Continue reading

Any Reason to Expect a Tipping Point with Arctic Sea Ice?

by Emil Morhardt

Williamson et al. (2016) examined the satellite data looking for signs of a tipping point in Arctic sea ice loss, but found none (my Jan 1 post). About the same time, Notz and Stroeve (2016) looked at the same data and did a simple linear correlation between September Arctic sea ice area and cumulative CO2 emissions since 1850. Voila! There was a strong negative linear correlation between the two showing a sustained loss of 3 ± 0.3 square meters of September sea ice area per cumulative metric ton of CO2 emission. Their title summarizes the result clearly: Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission. If this linear trend continues and there is no tipping point—and there is no reason to expect one—we can make a pretty good guess about the timing of the future of Arctic sea ice to the extent we can predict CO2 emission levels. At the rate we are going, September Arctic sea ice will be completely gone before mid-century (and global average temperatures will have risen more that 1.5ºC.) Furthermore, we can now get a feeling for how much our personal use of fossil fuels and the energy derived from the directly affects Arctic sea ice; the average CO2 release from personal use is several metric tons,  Continue reading