While climate change tends to be associated with extreme weather events or the long-term rise in global average temperature, a new study takes a different angle by considering what could happen to ‘mild’ weather conditions
January 19, 2017 — The research, published in Climatic Change, find that warm, dry days that are ideal for outdoor activities, construction work and travel could change dramatically by the end of the century.
While temperate countries such as the UK and US could see more mild days in future, tropical countries could see a decline of more than 50 days in the average year. This means more hot and humid days for the tropics, the researchers say, with fewer mild days to break up summer heatwaves.
But it’s important that that prospect of more mild weather in the northern hemisphere doesn’t distract from tackling climate change, other scientists tell Carbon Brief, as more severe extreme rainfall and heatwaves will also increase as the climate warms.
Outside of the UK, where the weather is a constant preoccupation, a spate of mild weather might not make it onto the front pages of the newspapers. But it’s still an important part of our day-to-day lives, says lead author Dr Karin van der Wiel, a postdoctoral research scientist at Princeton University and the Geophysical Fluid Dynamics Laboratory of the US National Oceanic and Atmospheric Administration. She tells Carbon Brief:
Largely overlooked in climate research, the new study attempts to fill the gap by creating a metric for “mild” weather and working out which countries could get less and which could get more.
Determining what counts as mild weather is tricky, says van der Wiel, as what a person thinks of as “mild” depends on where they live, the time of year and past experience. So van der Wiel and her colleagues created a relatively simple metric that they could apply across the world. She explains:
The map below shows how mild days are distributed across the world at the moment. The regions with dark blue shading have the most mild days each year, while the grey areas have none at all. Overall, there is currently a global average of around 74 days of mild weather per year.
In general, mild weather in tropical areas is hindered by being very wet and humid, the study says. Temperate regions tend to be limited by temperature – with winters in particular being too cold to be classified as mild. The map suggests that subtropical regions, such as South Africa and Australia, have the highest number of mild days. For example, Cape Town and Sydney get an average of 197 and 144 mild days per year, respectively.
Using a collection of climate models, the researchers estimated how mild weather across the world could change by the end of the century. They use a moderate scenario of future climate change called RCP4.5.
You can see their findings in the map below. Areas shaded orange or brown are expected to see a fall in the number of mild days, while those in green and blue are likely to see an increase.
Overall, the findings suggest the world will see an average of 10 fewer mild days by the end of the century. But regional changes are much larger, the study says.
Rising temperatures are projected to bring more days of mild weather in temperate countries such as the UK, US and Canada. For example, London could get an extra 24 mild days a year by the end of the century, while Los Angeles might get an extra six.
In contrast, hotter and more humid conditions will see decreases of over 50 mild days per year in large parts of tropical Africa, Asia and South America. Van der Wiel explains:
Lima in Peru is projected to lose 114 mild days in the average year, the researchers say, while Dakar in Senegal and Mumbai in India could see 57 and 44 fewer mild days per year, respectively.
As the results are under a moderate emissions scenario, the changes would be larger and occur earlier this century if emissions aren’t curbed, she adds.
Climate change mitigation
While the tropics will be most affected by changing mild weather, it’s the increases for temperate countries that troubles Dr Patrick Egan, associate professor of politics and public policy at New York University, who co-authored a similar study about recent increases in “pleasant” weather in the US. He tells Carbon Brief:
Although an increase in mild weather might sound desirable, it will come with other aspects of climate change too, notes van der Wiel:
Prof Richard Allan, professor of climate science from the University of Reading, who also wasn’t involved in the study, agrees. He tells Carbon Brief:
It’s also worth bearing mind that the study’s definition of “mild” is very broad, adds Allan:
This means there’s plenty of work to be done to refine this analysis for specific regions and countries, says van der Wiel: