The Science Media Centre recently held a briefing for journalists on the recent slowdown in global surface temperature rise, and published an accompanying briefing note. The Met Office also released three reports on the topic.
The key points were: (1) recent changes need to be put in longer term context & other climate indicators such as sea level, Arctic sea ice, snow cover, glacier melt etc are also important; (2) the explanation for recent slowdown is partly additional ocean heat uptake & partly negative trends in natural radiative forcing (due to solar changes and small volcanic eruptions) which slightly counteract the positive forcing from GHGs; (3) the quantification of the relative magnitude of these causes is still work in progress; (4) climate models simulate similar pauses.
There were several articles in the media following the briefing, including BBC, The Telegraph, The Independent, amongst others. One theme in the articles was that the possible existence of such pauses were a surprise to journalists, but not to the scientists. As the observations of global temperature have always shown such variability it should not have been too surprising, but perhaps this message was not expressed or communicated clearly to the media before? Or perhaps it just was not as interesting to the media before?
Early discussions on role of variability
Previous IPCC reports have certainly highlighted the role of variability – for example:
- FAR 1990: Simulated decadal variability was present in some of the first climate simulations (Figure 6.2). Also discussed in the Executive Summary of the SPM.
- TAR 2001: Section 18.104.22.168 – Signal versus noise, including Figures 9.2 and 9.3
One of the earliest coordinated efforts which considered the role of variability in projections was the EU PREDICATE project which ran from 2000 to 2003. Figure 1 below (published in CLIVAR Exchanges #19 in 2001) shows observations and three projections of European temperatures from 1996 to 2020 with different realisations of the variability. This type of work helped motivate the use of initial condition information to make experimental decadal climate predictions.
The communication of the role of variability has increased markedly since the IPCC AR4 (which was unfortunately a little quieter on this topic), at least partly due to the recent slowdown. Recent articles, such as that of Deser et al., have helped this communication.
Two figures used at the briefing also appear below. The first highlights that simulations do show similar pauses to those seen in recent observations, and the second, which appears in the briefing note, will be familiar to regular readers of Climate Lab Book. It compares the observed global temperatures with the CMIP5 simulations, but with a longer term context than previous versions.
Overall, the important role of variability in near-term climate has been known since the early climate simulations, but perhaps not communicated as widely as it might have been.