University of BristolLocating hotspots for climate change

Locating hotspots for climate change

University of Bristol

Extreme weather is costing lives – but new research that reveals the impact of global warming can help save them

Half a degree Celsius might not sound like much, but it could be the difference between life or death for thousands of people.

Researchers from the University of Bristol’s Climate Dynamics group have demonstrated how such a small temperature difference is already having a huge impact.

Eunice Lo, a research associate from the School of Geographical Sciences, led a study that found that thousands of heat-related deaths could potentially be avoided in major US cities if global temperatures are limited to the Paris Agreement climate goals.

The Paris Agreement aims to keep the increase in global average surface temperature well below 2°C above pre-industrial levels. The agreement ideally seeks to limit the increase to 1.5°C.

The study, a collaboration between UK and US climate scientists and epidemiologists, estimated changes in the number of heat-related deaths in 15 major US cities. It found that between 110 and 2,720 heat-related deaths per city could be avoided during extreme heat events, depending on the city, if warming is kept to 1.5°C.

However, if warming is limited to the upper Paris Agreement goal, fewer deaths – between 70 and 1,980 – could be avoided per city.

“My research mainly looks at extreme heat events, like extremely hot summers and heatwaves, because these are events that have a huge impact on human morbidity and mortality,” says Dr Lo.

“For individual US cities, including New York City and San Francisco, we estimated that if we limit global warming from 3°C, which is the current trajectory, to 1.5°C, then hundreds to thousands of extreme heat-related deaths could be avoided.”

Dann Mitchell, associate professor in atmospheric science, says the research group includes a broad spectrum of expertise, from theoretical climate modellers to climate impact scientists.

“Traditionally, this work has been done by climate scientists and then also by an impact modelling group separately. Our group brings together those two disciplines so that we can take the climate all the way through to the impact, which might be flooding or it might be heat-related mortality,” he says.

“Our research is focused mainly on extreme climate, for example, very high temperatures or very low temperatures, very high precipitation or very low precipitation, and how that impacts society.”

One of the group’s first significant projects focused on attributing heat mortality to climate change. The research, led by Dr Mitchell, looked at the 2003 heatwave in Europe. It found that in Paris, for example, climate change resulting from human greenhouse gas emissions made a significant contribution to heatwave deaths.

“Around 70 per cent of those who died during the heatwave lost their lives because of climate change. That’s about 30,000 to 40,000 people across Europe,” says Dr Mitchell.

The research, Dr Mitchell says, showed that climate change is already responsible for people losing their lives.

“In the climate community, we’ve done a lot of attribution science, and we come up with statements such as ‘It is extremely likely that we have contributed X degrees Celsius to global warming from human activities.’ But that doesn’t really capture people’s attention, because we don’t feel the global temperature, we feel the temperature in the cities where we live,” he says.

“By doing the attribution analysis on variables such as mortality, we actually start to demonstrate the current impacts of climate change.”

The Climate Dynamics group is part of the University of Bristol’s Cabot Institute for the Environment, which includes 600 experts working on a range of challenges with the aim of protecting the environment.

Collaborations are a theme of the group’s research, and academics regularly work with colleagues at universities in England and internationally. The University of Washington, in Seattle, was a partner in the study estimating heat-related deaths in US cities, for example.

Public Health England and the US-based Centers for Disease Control and Prevention and the Union of Concerned Scientists are also partnering with Bristol for research studies.

“We try to get through to those people who are informing the governments,” says Dr Mitchell.

“From school age, we have a way of constraining our thinking, where you have classes in maths and classes in science, and at degree level, you may have a degree in geography, for example.

“But actually, the only way the climate crisis can be resolved is not by putting things into silos, but by working across many different disciplines, from theoretical physics right the way through to social sciences.”

Raising awareness of the impact that climate change is already having on human health is key for people to understand the need to reduce their own carbon footprints, explains Dr Lo.

“Research shows that if we meet the Paris Agreement targets, especially the 1.5°C target, we can avoid a lot of climate-related risks to the natural system and also to our society,” she says.

“Individuals should be aware of the impact we’re having on the climate and vote for politicians who make policies they want to see in terms of protecting the environment and combating climate change.”

How the urban environment adds to rising regional temperatures is another interest of Dr Lo’s. She is currently investigating how future temperatures will change in central and suburban areas of specific UK cities. The group plans to work with Bristol City Council to identify “vulnerability hotspots” where heat action plans could be put into practice.

Two issues the researchers face are a lack of climate and mortality data from developing countries and the accuracy of complex future climate modelling. But modern scientific advances may provide a solution.

A PhD student in the research group intends to use machine learning techniques to fill in gaps in the climate data for developing countries. Quantum computing, meanwhile, could provide a way to precisely scale up climate models, including those used to help us predict future average temperatures.

“Our models are now so complex that our supercomputers are not able to run them at the speeds we want,” explains Dr Mitchell. “We’re hoping that quantum computing is going to take off. If it does, that would be great for climate science.”

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