We have seen months of weird, extreme weather. In the Northern Hemisphere feeling cold seems a distant memory as we swelter through a long hot summer as part of a global heatwave. Yet it has only been a few months since much of Europe was blanketed in snow and ice as the “Beast from the East” brought a bitterly cold wind from Siberia. At that time, the Arctic was seeing some record high winter temperatures, and the Arctic sea-ice maximum was the second lowest recorded – just higher than 2017’s record low.
And now it is hot, and the heatwave has had tragic consequences in some countries including Japan and Canada which have seen dozens of heat-related deaths. Temperatures in Spain and Portugal could exceed 48°C in the next few days, breaking the all-time Europe record for highest temperature ever recorded.
The science of attribution looks at “identifying a human fingerprint on individual extreme weather events” in a probabilistic way – i.e. how much more likely is an event due to our actions? Preliminary analysis by World Weather Attribution suggests this summer’s Northern European heatwave was more than twice as likely to have occured due to human activities altering the climate. So while it is not quite correct to say that any particular heatwave was caused by by climate change – we can say ‘this is precisely what we predicted climate impacts would look like’.
The risk of extreme hot weather has a relatively direct relationship with global warming – as the temperature rises (and 2017 has just been confirmed as the third hottest on record) then extremely hot weather becomes more likely as seen in the figure below.
Figure 2: The effect of changes in temperature distribution on extremes (based on Figure SPM.3)
While climate change links to heatwaves are direct, linking some other extreme events is less straightforward.
As an extreme weather event, drought is more insidious. Drought has different causes and unlike events such as floods or hurricanes or even heatwaves, it is not always clear when a drought has started or when to take action. Good management and sufficient water reservoirs mean that even extended periods without rain may lead to few negative impacts. In the UK the extended hot and dry spell has turned “England’s green and pleasant land” to brown – though talk of water restrictions have abated. Cape Town’s “Day Zero”, when taps run dry and people have to queue for water, has also been pushed back to 2019 – in part because the city’s inhabitants drastically reduced water consumption and the rains finally came.
Climate change can increase risk of drought as warmer air leads to more evaporation from land, rivers and lakes, and drier soils are less able to absorb any rainfall which does come.
Wildfires have been all over the news with the 2017 Californian wildfire season being among the most destructive and costly on record. In the past months we’ve seen the peat fire on Saddleworth moor in the UK, wildfires in Sweden up to the Arctic Circle and the tragic fires in mainland Greece. Wildfires are not weather events and other factors such as land management (to minimise flammable material) and ignition sources (from lightning strikes to cigarettes) are also determinants.
Climate change increases the risk of wildfires because warmer and drier weather creates the perfect conditions for wildfires to start, helps a burning fire to spread, and coupled with lack of water, can make them harder to stop.
What are the chances?
All such extreme events – heatwaves, drought and wildfires – are natural phenomena. They have happened before and will do so again. However, climate change makes them more likely to occur and to be more severe. Carbon Brief have mapped climate change and extreme weather for 144 studies – they find that 63% of all extreme weather events studied were made more likely or more severe by human-caused climate change.
Two analogies are commonly used on the link between climate change and extreme weather events:
- Climate change loads the dice: you can roll a six with a regular die but a six is more likely with a die that is loaded – however, you can’t say that any particular six is due to it being loaded.
- Climate change is like a baseball player on steroids: a player can hit a home runs when clean but if they get stronger with the aid of steroids then hitting a home run is more likely – however, you can’t say that any particular home run is due to the steroids.
Similarly, we can’t say that any particular extreme is caused by climate change but we can say they are more likely under climate change.
So we are expecting more extremes?
More extreme weather events and higher impacts from them is not unexpected. This is seen in the World Economic Forum’s most recent Global Risks Report (figure 3)
What can we do?
In October the Intergovernmental Panel on Climate Change will release its Special Report on Global Warming of 1.5°C. We don’t know what the final report will say but the underlying science confirmsshows that as the world warms, weather extremes and their impacts increase. Even just a half degree of extra warming between 1.5°C and 2°C can cause devastating impacts for many people and species.
Climate change is caused by us – from burning fossil fuels for energy to cutting down trees to make way for agriculture. The weird and extreme weather such as we’ve experienced this year threatens our health, our water supplies and our wildlife. We are in the age of consequences, and facing extreme events will become normal if we don’t act urgently to stop global temperatures rising. We must do this through rapid and deep cuts to greenhouse gas emissions.
Dr Stephen Cornelius is the Chief Advisor – Climate Change for WWF-UK. He is based in London. SCornelius@wwf.org.uk