Pause for thought

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Ed Hawkins, Doug McNeall and I have just had a commentary published called Pause for Thought. It’s part of a Nature Focus on the slowdown in global surface warming, which includes six commentaries plus new research by Seneviratne et al. on how the number of extreme hot days has continued increasing throughout the slowdown in the global average. Unfortunately it’s not open access, but the content is free for the next month with registration, and I can also put our article online in six months.

First, what is the slowdown? Since the late 1990s the global average surface temperature has increased more slowly than in the two decades before. In fact it is fairly flat, so it’s often called a pause or hiatus, though there is increasing evidence that it’s a slowdown not a complete stop.

Our piece is not about whether it is a pause or slowdown, or the various reasons this may have happened (one of them being a temporary increase in heat being transferred from the atmosphere to oceans). We write about communication of this topic, particularly online. It’s also the first Nature paper where the authors give their Twitter handles!

Climate model projections have shown periods of cooling of about this length, embedded within longer-term warming, since before this pause happened. But our communication of this expectation has not been good: it has been a surprise to public and journalists alike.

First, the IPCC Summaries for Policymakers have not been very clear that pauses could occur, at least until the most recent report (quotes from these are given in the article).

Second, climate scientists tend to show averages of many simulations, which smooths out any temporary changes in trend. Here is a figure that shows some individual simulations and how each one can have slowdowns at different times:

Hawkins_et_al_2014_NCC_Fig1a

The role of variability in global temperatures. Observed global mean surface air temperatures (solid black line) and recent 1998–2012 trend (dashed black line), compared with ten projections from a global climate model (grey lines). The grey shading is the 16–84% spread (smoothed for clarity). Two different simulations are highlighted (blue), and trends for specific interesting periods are shown (red, green, purple lines). The highlighted simulation shows a strong warming in the 1998–2012 period, but a 15-year period of no warming around the 2030s. [Figure 1a from Hawkins et al. (2014), Nature Climate Change].

Third, the causes of slowdowns are complex and sometimes the desire to simplify means communication has been plain wrong:

Although the most recent decade is the warmest since 1850, this does not mean there is no pause, as some have seemed to suggest.

As a rough guide to public interest in recent years, we included a Google Trends graph for related searches:

Hawkins_et_al_2014_NCC_Fig2

Quantity of Google searches for the terms ‘global warming stopped’ (blue) and ‘global warming pause’ (red) over the period from January 2007 to December 2013, expressed as ‘relative interest’ with the highest monthly total given an index of 100. Accessed on 23 Jan 2014 and subject to change. [Figure 2 from Hawkins et al. (2014) Nature Climate Change.]

We believe the increase for ‘global warming stopped’ in early 2008 was driven by this New Statesman article and the peak in October 2012 m by this piece in the Mail Online. From March 2013, ‘global warming pause’ appears to have been popularised by another article in the Mail Online and one in The Economist. The peak in September 2013 is due to media coverage of the Summary for Policymakers IPCC Fifth Assessment Report Working Group I. If you want you can see some videos of me grinning too much to try and look approachable while talking about the IPCC report.

We point out the very active discussions in the Twittersphere and blogosphere, “often discussing rather complex technical issues from the latest literature”, but note that the amount of content from climate scientists is hugely outweighed by that from commentators (on any point of the opinion spectrum).

So we call on our fellow scientists to join us in these online conversations. I talked in a recent Open University panel on social media and climate sciencerecording here — about “flooding the market” (no pun intended) with climate scientists. This shares the ‘load’ for us all, by involving more experts from different research areas, and shows climate science and scientists most directly. We give some general recommendations about engaging with the public online:

Although online conversations can be unpredictable, rambunctious and frustrating, they are often personally and professionally rewarding…From our experience, the online ‘audience’ is often technically proficient, but neither captive nor necessarily interested or patient, so conversations are more successful than lessons. We always expect, and try, to learn something from those we seek to ‘teach’. Where there is a genuine uncertainty we must not ignore it. We find that being defensive, over-confident or dogmatic are not successful strategies. Humour and humility are useful in keeping people on board and one’s sanity intact.

We believe the complexity of the science and the public interest in the pause are not ‘difficulties’ to be avoided or glossed over but instead provide a fantastic opportunity to dig into the details of the science.

We should see the pause as an opportunity, offering a clear hook to explore exciting aspects of climate science; to draw back the curtain on active scientific discussions that are often invisible to the public. The pause is a grand ‘whodunnit’ at the edge of our scientific understanding…The challenge is to embrace the complexity of the situation, to acknowledge the uncertainty and the nuance, to welcome questions and investigation and show the process of climate science in good health. Online engagement would seem to be essential in this endeavour.

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