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

Are There Early Warning Signals of Tipping Points in Arctic Sea Ice?

by Emil Morhardt

Everyone agrees that it would be helpful in making climate policy if we had some advance warning of climate tipping points. Williamson et al. (2016) set out to look for one associated with the melting of the Arctic sea ice. They asked if there is any evidence that the sea ice is about to undergo a local tipping point (which they also refer to as a bifurcation) that would lead to much faster melting. In the case of Arctic sea ice, the annual melting is caused by the summer sun, and a long-term parameter change that is enhancing it is the gradual buildup of CO2 in the atmosphere. Melting is limited partially by the fact that much of the incoming solar radiation is reflected back to space by the ice. A tipping point might be reached when enough of the ice is melted that the amount of sunlight absorbed by the ice-free open ocean begins to warm it faster each cycle. Although this study did not find any evidence for an imminent tipping point the authors noted that the sort of signal they were looking for might not occur until very close to a tipping point. That would, of course, make it useless for long-term policymaking. Their approach to looking for a signal is interesting though, and could be applied to many other potential climate tipping points. Continue reading