Summer temperatures 2018 – the ‘new normal’?

By Professor Sir Brian Hoskins (Grantham Institute, Imperial College London and Emeritus Professor at the University of Reading department of Meteorology) and Stephen Belcher (Met Office Chief Scientist and Visiting Professor at the University of Reading department of Meteorology)

Figure 1. Hyde Park, London, in a heatwave

There can be no doubt that the summer of 2018 has been remarkable both in the UK and across the world. Following an appearance on BBC Newsnight, in which the presenter Emily Maitlis asked if current temperatures can be considered the ‘new normal’, Professor Sir Brian Hoskins  and  Professor Stephen Belcher give their perspective of the heatwave and its connections to climate change.

In the UK the hot weather has been with us on and off since April. Some parts of East Anglia and southeast England have had virtually no rain in more than 55 days, and we may see our all time highest temperature record of 38.5°C fall by the end of this week.

The Arctic Circle has seen temperatures top 30°C, including at Badufoss and Makkaur in Norway, and in Finland temperatures have hit 33.4°C.

Meanwhile in Japan on Monday, the city of Kumagaya reported a new record temperature for the country, 41.1°C, and temperatures have exceeded 40°C in central Tokyo for the first time ever and there have been reports of many people being taken sick with heat stroke.

Naturally people are asking whether this is a result of climate change – is this the ‘new normal’. So what can we say?

Well, the atmospheric patterns leading to the UK heatwave do occur in the natural cycles in the weather, but they have been unusually persistent. The jet stream has weakened and got stuck to the north of the UK, with high pressure settled over the UK and Europe. In the summer such a pattern leads to dry soils, which means that if the sunny weather continues the energy of the sun is not used up in evaporating water and the temperatures rise even more.

In addition, we’ve seen a background of global warming due mostly to increased atmospheric greenhouse gases, with global mean temperatures rising more than 1°C above pre-industrial levels, and even more so over the northern continents. The natural cycles of weather mean that we shouldn’t expect heatwaves like this to happen every year but, when we do experience them, the warmer world means that there is an increased risk of even higher temperatures.

In 2003 Europe also experienced a pronounced heatwave. Research led at the Met Office showed that greenhouse gas concentrations in the atmosphere doubled the chance of the temperatures recorded in 2003 compared to what we’d expect in a pre-industrial world. This research also concluded that by the 2040’s the temperatures we saw in Europe in 2003 could be fairly normal in summer. We have updated this prediction with more recent data, and found that this prediction is still on track: the extreme temperatures we saw in the summer of 2003 can be expected to occur more regularly in Europe by the 2040s.

Figure 2. Summer mean temperatures anomalies over Europe (area in enclosed box) from CRUTEM4 observations (black), climate model simulations from CMIP5 (following RCP8.5) which include all forcings including greenhouse gases (red) and with only natural forcings (green). If greenhouse gas emissions are reduced to zero by 2050 the growth in temperature would cease.

At the Met Office, in collaboration with the universities, scientists are carrying out a detailed analysis of this particular heatwave and its expression in a warming world. Scientists are aiming to understand why the weather pattern this summer was so persistent, and to what extent this persistence may be influenced by human-induced climate change, as well as the role of global warming by greenhouse gases in raising the temperatures experienced in the heatwave. Findings will be published later in the year.

The temperatures we are currently experiencing may not yet be the ‘new normal’, but within a few decades they could be.

[Image credit: Stephen Craven]


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