I’ve been away at a meeting where there talks from 9am till about 6pm and then various evening activities. I then came back to work and spent yesterday marking undergraduate research presentations. So, I haven’t had a chance to post anything. Interestingly, some of the student presentations were about climate change. Strangely, noone concluded with “and I discovered it was all a big scam” and some even some said things – without even a hint of irony – that would be regarded by some as rather alarmist.
Since there’s been some recent interest in whether or not the Equilibrium Climate Sensitivity (ECS) was probably greater than 2pC, I thought I might briefly highlight a new paper. It’s by Johansen et al. and is called Equilibrium climate sensitivity in light of observations over the warming hiatus and has already been discussed in some detail in this Carbon Brief post.
I haven’t had a chance to go through it in fine detail, but it is essentially an energy balance approach that also incorporates other factors (like ENSO and other internal variability) to estimate ECS. The table below compares the model trends with the observed trends, and also shows how the different factors contribute to the trends.
The interesting figure is the one on the right, which shows how the range for ECS changes with time. Essentially, as we consider longer time intervals and more data, the upper limit comes down, the range is reduced, but the lower limit (of the 90% confidence interval) remains around 2oC. They also manage to constrain the Effective Vertical Diffusion (EVD) which is important for determing ocean heat up take.
However, one should still be a little careful. The paper itself ends with
Finally, although we find that the inclusion of observations over the hiatus period contributes to a more constrained estimate of ECS, the degree to which this was due to the hiatus per se, as opposed to the accumulation of more data in general, is unclear. In addition, we also find that the PDF of ECS shifts back and forth as observations accumulate. This indicates that unforced natural variability plays a key role for the estimate of the PDF of ECS (ref. 15). ….. Further, limitations and uncertainties in the structural relationships in geophysical models as well in statistical models hamper any observationally based estimate of ECS, implying that all empirical estimates of ECS should be interpreted with some care.
I’ll finish post by linking to the slides from Bjorn Stevens talk at Ringberg (H/T to MarkB) and to the letter he’s released pointing out that his recent aerosol forcing paper doesn’t immediately imply a significant reduction in ECS. Anyway, that’s enough from me. Hope everyone has a nice Easter break, if you’re having one. If not, have a nice weekend 🙂