Limiting global warming to 1.5°C would reduce risks to humans by up to 85%

New research led by the University of East Anglia (UEA) quantifies the benefits of limiting global warming to 1.5°C and identifies the hotspot regions for climate change risk in the future.

The study calculates reductions in human exposure to a series of risks -- water scarcity and heat stress, vector-borne diseases, coastal and river flooding -- that would result from limiting global warming to 1.5°C rather than 2°C or 3.66°C. Effects on agricultural yields and the economy are also included.

Researchers from the UK, including scientists from UEA and the University of Bristol, and from PBL Netherlands Environmental Assessment Agency, find that the risks are reduced by 10-44% globally if warming is reduced to 1.5°C rather than 2°C.

Currently, insufficient climate policy has been implemented globally to limit warming to 2°C, so the team also made a comparison with risks that would occur with higher levels of global warming.

Risks will be greater if global warming is greater. The risks at 3.66°C warming are reduced by 26-74% if instead warming is kept to only 2°C. They are reduced even further, by 32-85%, if warming can be limited to just 1.5°C. The ranges are wide because the percentage depends on which of the indicators, for example human exposure to drought or flooding, are being considered.

The findings, published today in the journal Climatic Change, suggest that in percentage terms, the avoided risk is highest for river flooding, drought, and heat stress, but in absolute terms the risk reduction is greatest for drought.

The authors also identify West Africa, India and North America as regions where the risks caused by climate change are projected to increase the most with 1.5°C or 2°C of average global warming by 2100.

The study follows the Intergovernmental Panel on Climate Change(IPCC) Sixth Assessment Report, which finds that global net zero CO2 emissions must be reached in the early 2050s to limit warming to 1.5°C with no or limited overshoot, and around the early 2070s to limit warming to 2°C.

Lead author Prof Rachel Warren, of the Tyndall Centre for Climate Change Research at UEA, said: "Our findings are important because the Paris Agreement target is to limit global warming to 'well below' 2°C and to 'pursue efforts' to limit it to 1.5°C. This means that decision makers need to understand the benefits of aiming for the lower figure.

"In addition, at COP26 last year, the commitments made by countries in terms of greenhouse gas emission reductions are not sufficient to achieve the Paris goals. At present, current policies would result in average warming of 2.7°C, while the Nationally Determined Contributions for 2030 would limit warming to 2.1°C.

"While there are a number of planned additional actions to reduce emissions further, potentially limiting warming to 1.8°C in the most optimistic case, these still need to be delivered and further additional action is needed to limit warming to 1.5°C."

For this study the researchers ran sophisticated computer simulations of climate change risk, using a common set of climate change scenarios in which global temperatures rise by 2°C and separately by 1.5°C and 3.66°C. They then compared the results.

The findings include:
 

• Overall, global population exposure to malaria and dengue fever is 10% lower if warming is constrained to 1.5°C rather than 2°C.
• Population exposure to water scarcity is most evident in western India and the northern region of West Africa.
• A continuous increase in global drought risk with global warming is estimated, with hundreds of millions of people additionally affected by drought at each, successively higher warming level.
• By 2100 if we do not adapt, global warming of 1.5°C would place an additional 41-88 million people a year at risk from coastal flooding globally (associated with 0.24-0.56 m of sea-level rise), whereas an additional 45-95 million people a year would be at risk under global warming of 2°C (corresponding to 0.27-0.64 m of sea-level rise) in 2100.
• Global economic impacts of climate change are 20% lower when warming is limited to 1.5°C rather than 2°C. The net value of damages is correspondingly reduced from 61 trillion US dollars, to 39 trillion US dollars.

The study used 21 alternative climate models to simulate the regional patterns of climate change corresponding to 2°C warming and 1.5°C warming respectively. Previous research has used simpler models, a more limited range of climate models, or has covered different risk indicators.

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Higher risk of temperature-related death if global warming exceeds 2°C

The death rate linked to extreme temperatures will increase significantly under global warming of 2°C, finds a report by researchers from UCL and the University of Reading.

Temperature-related mortality -- where a death is directly linked to climate temperature -- in England and Wales during the hottest days of the year will increase by 42% under a warming scenario of 2°C from pre-industrial levels. This means an increase from present-day levels of around 117 deaths per day, averaged over the 10 hottest days of the year, to around 166 deaths per day. The findings underline the importance of keeping global warming levels to below 2°C.

At current global warming levels of around 1.21°C we see a slight decrease in temperature-related mortality in winter and a minimal net effect in summer, meaning that overall, at this level of warming we see a slight decrease in temperature-related mortality rate.

In the paper, published in Environmental Research Letters, the team examined the impact of climate change on temperature-related mortality rates in England and Wales, focusing on the risk from heat in summer and cold in winter. They found that as the global mean temperature increases, temperature-related mortality in summer will increase at a much faster, non-linear rate.

The rate of increase particularly speeds up at 2°C of warming, with a much higher risk appearing beyond 2.5°C. The researchers say that 3°C warming could lead to a 75% increase in mortality risk during heatwaves.

When plotted on a graph, the relationship between temperature and mortality is roughly u-shaped, meaning that at extremely high temperatures, which the population is not used to, the mortality risk increases sharply for each degree rise of daily mean temperature.

The rate in winter will continue to decrease, although this doesn't take side effects of extreme weather -- such as storms -- into account.

Lead author Dr Katty Huang (UCL Civil, Environmental & Geomatic Engineering) said: "The increase in mortality risk under current warming levels is mainly notable during heatwaves, but with further warming, we would see risk rise on average summer days in addition to escalating risks during heatwaves. What this means is that we shouldn't expect past trends of impact per degree of warming to apply in the future. One degree of global warming beyond 2°C would have a much more severe impact on health in England and Wales than one degree warming from pre-industrial levels, with implications for how the NHS can cope."

In England and Wales, temperature is associated with around 9% of total population mortality, meaning that 9% of all deaths during 2021 could be associated with the temperature. Most of those deaths are related to the side effects of cold weather.

The team analysed the 2018 UK Climate Projections (UKCP18) with data on present-day temperature and mortality in order to predict changes in temperature-related mortality relative to degrees of global warming.

In order to isolate the effects of global warming on mortality risk, the researchers looked at the potential impact for the current population, without taking into account future changes such as average age and health conditions.

Read more at Science Daily