The new book about Contemporary Climate Change Debates, that I discussed in this post, includes a debate about whether or not ‘tipping point[s]’ [are] helpful for describing and communicating possible climate futures? James Annan suggests that the answer is “no”, while Michel Crucifix suggests that it’s “yes”.
James discusses his essay briefly in this post and you can download a copy of his essay here. I have read Michel’s essay, but I don’t have a copy that I can post publicly. I think James is right that they were somewhat talking past each other.
I share some of James’ concerns about introducting tipping points into the public narrative. People do sometimes seem to confuse tipping points and a runaway, which is what motivated me to write this post. For clarity, a tipping point is a threshold beyond which some part of the climate system changes (tips), irreversibly, into a new state. A runaway, on the other hand, is a state where the outgoing flux is limited, resulting in substantial surface warming, with the system only returning to energy balance when the temperature has increased by 100s of K. The latter is simply not possible in our current state.
Another issue with tipping points is that we don’t know if they are truly irreversible; if we could start to artificially draw down atmospheric CO2 might some then reverse? Additionally, the timescale over which they manifest themselves is typically long, in many cases centuries. Hence, they don’t necessarily imply a need for urgent action.However, it is certainly the case that there are thresholds beyond which certain systems may start to undergo changes that might prove very difficult to reverse. As the figure on the right (from Schellnhuber et al. 2016) illustrates, it may already be too late to avoid the death of most tropical coral reefs. Similarly, we may already be close to the point where the Greenland and West Antarctic ice sheets start to melt irreversibly, and where we may lose the summer Arctic sea ice and Alpine glaciers.
If we warm as much as 4C, then we risk the loss of the Amazon and Boreal forests and could irreversible change weather patters in the Sahel. Beyond 4C, we risk the irreversible loss of permafrost, the East Antartic ice sheet may start irreversibly melting, and we could lose winter Arctic sea ice.
So, some may be triggered relatively soon, while others are unlikely to be triggered unless climate sensitivity is much higher than we expect, or we end up emitting much more than currently seems likely. Therefore, we do have to be careful of how we introduce these into the public narrative, but I see no real reason why we shouldn’t do so.
We typically motivate climate action on the basis of warming leading to climate impacts that will become increasingly severe if we fail to limit our emissions. I don’t think the existence of possible tipping points specifically changes what we should do; it is simply a further indication that we should be doing our best to limit how much we emit. Although the impact of crossing a tipping point may only manifest itself on long timescales, it does seem clear that if we do cross some of these thresholds, reversing these changes will be extremely difficult. Just like we may want to give ourselves a reasonable chance of avoiding the impacts of, for example, >2C of warming, we may also want to avoid discovering if this level of warming could also trigger irreversible changes in some parts of the climate system.