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Could we control our climate?
Could we control our climate?

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1 Are climate models wrong?

In March 2013, the Mail on Sunday reported that climate model predictions of GMST are ‘a spectacular miscalculation’ (Figure 2).

Figure 2 is a screenshot of an online newspaper article. Figure 2a shows the article headline 'The Great Green Con no 1: The hard proof that finally shows global warming forecasts that are costing you billions were WRONG all along'. The article is by David Rose for the Mail on Sunday, published 23:37 16 March 2013. Figure 2b hows a graph of temperature anomaly forecasts on the y or vertical axis (from -0.5 to +0.5 °C) against year on the x or horizontal axis (from 1950 to 2030). The anomaly increases from about - 0.2 °C in 1950 to + 1.2 °C by 2030. The temperature forecast includes 75% and 95 % confidence ranges. A black line shows observations of temperature which are shown to lie largely within the 75% confidence range up to 2005, then starts to fall below it, appearing to fall outside and below the 95% confidence range by 2013.
Figure 2 Evaluating models, as reported by the Mail on Sunday, March 2013: (a) headline; (b) accompanying graph based on figure produced by Ed Hawkins.

Emotive accusations

The Mail on Sunday article was published six months before the IPCC (2013) report and claims that climate model predictions of GMST are ‘a spectacular miscalculation’ because the observed GMST is ‘about to crash out of’ their range.

Given this media environment and the use of emotive language, how can the public assess the quality of media reporting about new climate studies?

Finding reliable information online is too large a topic to cover here. But if you want to hear directly from climate scientists, you could try [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , a network of climate scientists that comment directly on news articles about their accuracy. Other useful and reliably accurate sources are the climate scientist list on Twitter flimsin/ lists/ climatescientists Carbon Brief.

So were the climate models ‘wrong’, as the Mail on Sunday headline said? Important questions to consider are:

  1. Was it a fair comparison?
  2. How does the comparison look now?
  3. Once the comparison is fair and up-to-date, how much can you learn from it?

Fair comparison

The graph in the Mail on Sunday report says the dark and light red envelopes are the 75% and 95% ranges. In fact, this is an error: they are the 50% and 90% ranges. In other words, the key implies a worse match than it is, so the description of the comparison is not fair.

Full comparison

The observations do show a 15-to 20-year slowdown in the rate of global warming from around 1998 (a record high year, due to a large El Niño) to around 2014. This was often called the ‘pause’ or ‘hiatus’.

Several years have now passed since. On 20 January 2016, the world’s media announced the 2015 mean temperature: the record-breaking year had a dramatic effect on the dataset (Figure 3).

Figure 3 is a graph showing Global Surface Temperature anomaly in °C, relative to the 1961 - 1990 average, on the y or vertical axis (from -0.8 to +1.0) against year on the x or horizontal axis (1850 - 2015). Three similar data sets of global surface temperature anomalies are shown as line graphs: Met Office, NASA and NOAA. All three lines show an increase from around -0.3 °C in 1850 to 0 °C around 1940, increasing to + 0.8 °C by 2015. The global mean temperature in 2016 and 2017 has remained at similar levels. So there seems to have been a shift in the climate narrative: the ‘pause’ button appears to have been replaced with ‘play’. Whether this is a long-term increase in warming or a brief fluctuation remains to be seen. Alternatively, entirely new stories about GMST may emerge.
Figure 3 The 2015 update to the GMST reconstructions: animated graphic by the blog ‘Carbon Brief’, January 2016.
  • Does a comparison of GMST from 1997 to 2016 (Figure 3) provide enough information to judge whether the model predictions were ‘wrong’ (as the Mail on Sunday put it) about global warming?

  • Not with great confidence. The period is twenty years, far short of the usual 30-year definition of climate (Session 1). This means it is not a fair test, because climate predictions are only intended to be correct over the longer-term.

However, the longer-term climate model prediction does indeed appear to be successful. Of course, even this is not enough information to judge whether the model predictions were ‘wrong’: GMST is just one aspect of climate change. To test the reliability of climate models, we should – and do – compare with observations of all parts of the Earth system.