Will July’s heat become the new normal?

Saddleworth Moor fire near Stalybridge, England, 2018. Image credit: NASA

For the past month, Europe has experienced a significant heatwave, with both high temperatures and low levels of rainfall, especially in the North. Over this period, we’ve seen a rise in heat-related deaths in major cities, wildfires in Greece, Spain and Portugal, and a distinct ‘browning’ of the European landscape visible from space.

As we sit sweltering in our offices, the question on everyone’s lips seems to be “are we going to keep experiencing heatwaves like this as the climate changes?” or, to put it another way, “Is this heat the new norm?”

Leo Hickman, Ed Hawkins, and others, have spurred a great deal of social media interest with posts highlighting how climate events that are currently considered ‘extreme’, will at some point be called ‘typical’ as the climate evolves.

In January 2007, the BBC aired a special programme presented by Sir David Attenborough called "Climate Change - Britain Under Threat".

It included this imagined weather forecast for a "typical summer's day" in 2020... pic.twitter.com/jrDJnb4yWt
— Leo Hickman (@LeoHickman) August 1, 2018

As part of a two-year project on how future climate impacts different sectors (www.happimip.org), my colleagues and I have been developing complex computer simulations to explore our current climate as well as possible future climates. Specifically, we’re comparing what the world will look like if we meet the targets set out in the Paris agreement: to limit the global average temperature rise to a maximum of 2.0 degrees warming above pre-industrial levels but with the ambition of limiting warming to 1.5 degrees.

The world is already around 1 degree warmer on average than pre-industrial levels, and the evidence to date shows that every 0.5 degree of additional warming will make a significant difference to the weather we experience in the future.

So, we’ve been able to take those simulations and ask the question: What’s the probability of us experiencing European temperatures like July 2018 again if:

We don’t emit any further greenhouse gases and things stay as they are (1 degree above pre-industrial levels).
Greenhouse gas emissions are aggressively reduced, restricting global average temperature rise to 1.5 degrees above pre-industrial levels.
Greenhouse gas emissions are reduced to a lesser extent, restricting global average temperature rise by 2 degrees above pre-industrial levels.

What we’ve found is that European heat of at least the temperatures we have experienced this July are likely to re-occur about once every 5-6 years, on average, in our current climate. While this seems often, remember we have already experienced 1C of global increase in temperature. We’ve also considered the temperature over the whole of Europe, not just focusing on the more extreme parts of the heatwave. If we considered only the hottest regions, this would push our current temperature re-occurrence times closer to 10-20 years. However, using this Europe-wide definition of the current heat event, we find that in the 1.5C future world, temperatures at least this high would occur every other year, and in a 2C world, four out of five summers would likely have heat events that are at least as hot as our current one. Worryingly, our current greenhouse gas emission trajectory is leading us closer to 3C, so urgent and coordinated action is still needed from our politicians around the world.

Our climate models are not perfect, and they cannot capture all aspects of the current heatwave, especially concerning the large-scale weather pattern that ‘blocked’ the cooler air from ending our current heatwave. These deficiencies increase the uncertainty in our future projections, but we still trust the ball-park figures.

Whilst these results are not peer-reviewed, and should be considered as preliminary findings, it is clear that the current increased heat experienced over Europe has a significant impact on society, and that there will be even more significant impacts if we were to begin experiencing these conditions as much as our analysis suggests.

Cutting our emissions now will save us a hell of a headache later.

-----------------------------
This blog is written by Dr Dann Mitchell (@ClimateDann) and Peter Uhe from the University of Bristol Geographical Sciences department and the Cabot Institute for the Environment.

Dann Mitchell

Peter Uhe

Converting probabilities between time-intervals

This is the first in an irregular sequence of snippets about some of the slightly more technical aspects of uncertainty and risk assessment. If you have a slightly more technical question, then please email me and I will try to answer it with a snippet. Suppose that an event has a probability of 0.015 (or 1.5%) of happening at least once in the next five years. Then the probability of the event happening at least once in the next year is 0.015 / 5 = 0.003 (or 0.3%), and the probability of it happening at least once in the next 20 years is 0.015 * 4 = 0.06 (or 6%). Here is the rule for scaling probabilities to different time intervals: if both probabilities (the original one and the new one) are no larger than 0.1 (or 10%), then simply multiply the original probability by the ratio of the new time-interval to the original time-interval, to find the new probability. This rule is an approximation which breaks down if either of the probabilities is greater than 0.1. For example

1-in-200 year events

You often read or hear references to the ‘1-in-200 year event’, or ‘200-year event’, or ‘event with a return period of 200 years’. Other popular horizons are 1-in-30 years and 1-in-10,000 years. This term applies to hazards which can occur over a range of magnitudes, like volcanic eruptions, earthquakes, tsunamis, space weather, and various hydro-meteorological hazards like floods, storms, hot or cold spells, and droughts. ‘1-in-200 years’ refers to a particular magnitude. In floods this might be represented as a contour on a map, showing an area that is inundated. If this contour is labelled as ‘1-in-200 years’ this means that the current rate of floods at least as large as this is 1/200 /yr, or 0.005 /yr. So if your house is inside the contour, there is currently a 0.005 (0.5%) chance of being flooded in the next year, and a 0.025 (2.5%) chance of being flooded in the next five years. The general definition is this: ‘1-in-200 year magnitude is x’ = ‘the current rate for eve

Coconuts and climate change

Before pursuing an MSc in Climate Change Science and Policy at the University of Bristol, I completed my undergraduate studies in Environmental Science at the University of Colombo, Sri Lanka. During my final year I carried out a research project that explored the impact of extreme weather events on coconut productivity across the three climatic zones of Sri Lanka. A few months ago, I managed to get a paper published and I thought it would be a good idea to share my findings on this platform. Climate change and crop productivity There has been a growing concern about the impact of extreme weather events on crop production across the globe, Sri Lanka being no exception. Coconut is becoming a rare commodity in the country, due to several reasons including the changing climate. The price hike in coconuts over the last few years is a good indication of how climate change is affecting coconut productivity across the country. Most coconut trees are no longer bearing fruits and thos

Cabot Institute for the Environment blog

Search This Blog