Study shows climate change poses risks to health and agriculture

As global temperatures rise, people in the tropics, including places like India and Africa’s Sahel region, will likely face dangerously hot conditions almost daily by the end of the century. even as the world reduces its greenhouse gas emissions, according to a new study.

Mid-latitudes, including the United States, will also face increasing risks. There, the number of dangerously hot days, marked by temperatures and humidity high enough to cause heat exhaustion, is expected to double by the 2050s and continue to rise.

In the study, scientists looked at population growth, economic development patterns, energy choices and climate patterns to project how heat index levels the combination of heat and humidity will change over time. Editors at The Conversation asked University of Washington atmospheric scientist David Battisti, co-author of the study, published August 25, 2022, to explain the findings and what they mean for humans around the world.

Question: What does the new study tell us about future heat waves and, above all, the impact on people?

Answer: There are two sources of uncertainty regarding future temperature. One is how much carbon dioxide humans will emit – this depends on factors such as population, energy choices and the growth of the economy. The other is the magnitude of the warming that these greenhouse gas emissions will cause.

In both cases, scientists have very common sense the likelihood of various scenarios. For this study, we combined these estimates to get a probability in the future of having dangerous and life-threatening temperatures.

We looked at what these “dangerously high” and “extremely dangerous” levels on the heat index would mean for everyday life in the tropics and mid-latitudes.

“Dangerous” in this case refers to the likelihood of heat exhaustion. Heat exhaustion won’t kill you if you can stop and slow down — it’s characterized fatigue, nausea, slow heart rate, possibly fainting. But you really can’t work in those conditions.

The heat index indicates when a person is likely to reach this threshold. The National Weather Service defines “dangerous” as a heat index of 103 F (39.4 C) and “extremely dangerous” as 125 F (51.7 C). If a person reaches “extremely dangerous” temperatures, it can lead to heatstroke. At this level, you have a few hours to get medical attention to cool your body, or you will die.

“Extremely dangerous” heat index conditions are almost unheard of today. They occur in a few places near the Gulf of Oman, for example, for maybe a few days over a decade.

But the likelihood of the number of “dangerous” days increases as the planet heats up. We will likely have about the same weather variability as today, but all of this is happening on top of a higher average temperature. Thus, the likelihood of extremely hot conditions increases.

What does your study show for each region?

Climate change photo illustration

At mid-latitudes by 2050, we will see the number of dangerous heat days double in the most likely future scenario – even with modest greenhouse gas emissions that would meet the Paris Climate Agreement goal to keep warming below 2 C (3.6 F).

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In the southeastern United States, the most likely scenario is that people will experience a month or two of dangerously hot days every year. The same is probably true in parts of China, where some areas sweated through a summer 2022 heat wave for more than two consecutive months.

We have found that by the end of the century, most mid-latitude locations will see a three to tenfold increase in the number of dangerous days.

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In the tropics, as parts of India, heat index at this time may exceed the dangerous level for a few weeks a year. It’s been like that for 20 to 30 years. By 2050, these conditions will likely occur for several months each year, we found. And by the end of the century, many places will experience these conditions most of the year.

What this means in practice is that if you’re a wealthy country like the US, most people can afford or find air conditioning. But if you’re in the tropics, where about half of the world’s population lives and where poverty is higher, heat is a bigger problem for much of the year. And a large percentage of people work outside in agriculture.

As we approach the end of the century, we will begin to exceed “extremely dangerous” conditions in several places, primarily in the tropics.

North India could see more than a month a year in extremely dangerous conditions. The Sahel region of Africawhere poverty is widespread, could experience a few weeks of extremely dangerous conditions per year.

Can humans adapt to what looks like a dystopian future?

If you’re a wealthy country, you can build cooling plants and generate electricity to run air conditioners – hoping they won’t be powered by fossil fuels, which would further warm the planet.

If you are a developing country, a very large part of the population works outside in agriculture to earn money and buy food. There, if you think about it, there aren’t many options.

Migrant workers in the United States also face more difficult conditions. A farm may be able to provide cooling facilities, but farmers’ margins are quite low and migrant workers are often paid by volume, so when they are not picking they are not being paid.

Eventually, conditions will reach the point where more workers will overheat and die.

Heat will also be a problem for crops. We are waiting most major cereals are less productive in the future due to heat stress. At mid-latitudes right now, we are close to optimum temperatures for growing grain. But as temperatures increase, grain yield decreases. In the tropics, it could be anywhere between 10% and 15% reduction per degree Celsius increase. It’s a pretty big hit.

What can be done to avoid these risks?

Part of our job in this study was to determine the chances of the world actually complying with the Paris agreement. We found it to be around 0.1%. Basically, it won’t happen.

By the end of the century, we have found that the most likely scenario is that the planet will experience a global warming of 5.4 F (3 C) relative to pre-industrial times. The land is warming faster than the ocean, which translates to an increase of around 7 F (3.9 C) for the places where we live, work and play – and you can get a glimpse of the future .

The sooner renewables come online and the more the use of fossil fuels is stopped, the better the chances of avoiding this.

David Battisti is a professor of atmospheric science at the University of Washington. This article is republished from The Conversation under a Creative Commons license.