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A look at how our warming planet could impact on deaths

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Over the past few years PHE has been involved in investigating the various threats climate change is likely to have on health in the UK. Risks include increased flooding, the potential for new infectious diseases becoming established, and prolonged pollen seasons as invasive plants flourish in a climate more suitable for their growth.

But the most direct impact of climate change will be through changes in temperature which directly affects risks to health.

In the UK the majority of temperature related health impacts are currently from cold, rather than hot weather and this will continue to be the case in the future.

Modelling suggests that in future decades the number of those dying from cold effects during winters will decrease and those dying from heat related conditions in summer will increase. However, the UK population is increasing and ageing, which means that even more people will be at risk from both hot and cold weather in the future.

What will happen when things warm up?

One question scientists are interested in is how much our climate will warm, and what will that mean for death rates in the future. We don’t know the exact answer because there are so many things to consider, not least the uncertainty in predicting how much greenhouse gas emission there will be and because of that how much temperature will change in future.

That’s why work is ongoing among scientists around the world to use a range of global climate models for various emission scenarios to try to determine the potential health impacts of increasing temperatures in future.

There are many factors to be considered; some studies use different sets of climate models, calculate health effects using different types of models, focus on high or low emissions scenarios, or consider the added effects of changing populations.

A major new paper, just published in the Lancet Planetary Health, explores this very issue, using a unique global dataset.

The study considered over 450 locations in 23 countries around the world and predicted what could happen in terms of health, if average global temperatures rise by up to around 5oC by the end of the century, but also what impacts could be avoided if temperature rose by much smaller amounts, in line with the Paris agreement to limit Global Warming to 1.5 or 2oC.

The paper aims to isolate the effects of changing temperature on mortality only, and so does not consider other potential changes, for example, in future population growth.

The authors calculated changes in death rates for northern and southern Europe, East and South Asia, Australia and North and South America, under three temperature scenarios resulting from different greenhouse gas emission levels.

Of course any temperature increase will have many impacts on health, some of which are less obvious than others, but what this paper has attempted to do is consider the direct impact temperature increases alone will have on the number of deaths.

What do the results say?

The results highlight geographical variations, patterns and complexity. For most of the global regions considered, the high-end temperature scenarios show substantial increases in heat deaths, particularly in the tropics, which are minimised under lower temperature change scenarios.

Some cooler regions show decreases in cold deaths as well as increases in heat deaths in future, although the decreases in cold deaths are likely to be offset once growth in population is factored into the calculations.

The paper also found that most of the health effects directly related to temperature increase could be avoided under scenarios involving mitigation strategies to limit emissions and further warming of the planet.

Since this paper isolates the effect of temperature changes in the future, it’s important to stress what this paper does not include. It doesn’t include the way global populations are anticipated to change over the coming decades. For example, it doesn’t account for how populations will grow, age or experience changes in underlying health status.

Also, it doesn’t explore the relative uncertainties found in climate projections, including potential underestimations of the scale of the urban heat island, the effect by which urban areas are warmer than surrounding rural ones because of the way man made surfaces affect local heating and cooling compared with natural surfaces. In addition, it doesn’t account for how populations might adapt to hot or cold weather in the future.

Whilst work has been done incorporating some of these factors into studies before, this new study presents a series of scenarios for different parts of the world using the biggest global dataset yet and allows us to examine how risks vary globally.

We hope this work will inspire global leaders to really commit to fulfilling the climate pledges made in Paris in 2015, to keep global warming to well under 2oC. But for me what this paper really highlights is the ongoing need for high quality climate and health research.

Work which delves deeper and in greater detail to specific aspects, so that policy makers around the world can ensure global efforts to mitigate climate change are built on a solid, scientific base.

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