Preface. Due to limits of human heat tolerance, much of Earth’s surface may not be habitable by 2300 if we continue to emit greenhouse gases at the current rate.
But we can’t continue at the current rate. Peak oil production probably peaked in 2018 (see citations in chapter 2 of my book Life After Fossil Fuels). IPCC models assumed we would be burning fossils until 2400 at exponentially increasing rates because they included resources in their calculations, while the reserves that can actually be exploited are a fraction of that amount. So the worst predictions are not likely to happen, but the effects will be plenty bad, and already are in many places, just not extinction or a hothouse earth.
Extreme heat events could lead to a tipping point in regional politics or social stability. In Africa, extreme droughts and high temperatures have been linked to an increase of risk of civil conflict and large-scale humanitarian crisis in Africa.
Alice Friedemann www.energyskeptic.com Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”. Women in ecology Podcasts: WGBH, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity, Index of best energyskeptic posts
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Xu C et al (2020) Future of the human climate niche.
As the climate continues to warm over the next half-century, up to one-third of the world’s population is likely to live in areas that are considered unsuitably hot for humans. Today fewer than 25 million people live in the world’s hottest areas, most of them in the African Sahara region. But by 2070 such extreme heat could encompass a much larger part of Africa, as well as parts of India, the Middle East, South America, Southeast Asia and Australia. With global population projected to rise to about 10 billion by 2070, that means as many as 3.5 billion people living in these areas. If this forces many to migrate, that would cause massive economic and societal disruptions.
Higher Heat effects on habitability
Well-known threats like rising oceans and economic depressions are not nearly as serious as the potential heat that might make the world, thermally, partly or completely uninhabitable by humans (SD 2010, McMichael 2010, Sherwood 2010).
Most heat on the planet is dry, and we can handle that, but we’re not adapted to surviving very humid heat — a wet-bulb temperature of over 95 F — for more than six hours, even if we’re resting in well-ventilated shade. Hot, humid heat leads to hyperthermia, heat stress, and eventually death. Heat stress is already a leading cause of fatalities.
What will happen when temperatures rise this much:
- 4 °C: would subject over half the world’s people to unprecedented heat
- 7 °C: some regions may become uninhabitable
- 10 °C: the amount of land that would become uninhabitable from heat stress is far more that what we’ll lose from rising sea levels
- 11-12 °C: would expand these regions to include most of today’s human population
It’s unlikely we’ll adapt with air-conditioning due to limited fossil fuels, nor would AC protect livestock or outside workers, and power failures would be life-threatening.
Why heat kills
The reason crowded indoor theaters get so hot is because everyone is radiating heat like a 100 Watt light-bulb. Normally this heat is carried away by sweating, heat conduction, and other radiative cooling. But when the air is very moist and hot, the second law of thermodynamics does not allow us to lose heat when the wet bulb temperature (TW) exceeds 95 °F for a long period.
We all have core body temperatures around 98.6 °F regardless of climate, and our skin is lightly cooler, about 95, so that metabolic heat is conducted to the skin. If our skin sustains temperatures above 98, then our core temperatures will rise even more, and once our core reaches about 108 F for any length of time, we’re likely to die of hyperthermia, no matter how acclimated and fit a person is.
Heat waves cause heat exhaustion, heat cramps, and heat stroke; heat waves are one of the most common causes of weather-related deaths in United States. Summertime heat waves will likely become longer, more frequent, more severe, and more relentless with decreased potential to cool down at night. Increases in heat-related deaths due to climate change are likely to outweigh decreases in deaths from cold snaps. In general, heat waves and the associated health issues disproportionately affect more vulnerable populations such as the elderly, children, those with existing cardiovascular and respiratory diseases, and those who are economically disadvantaged or socially isolated. Increasing temperature and humidity levels can cross thresholds where it is unsafe for individuals to perform heavy labor (below a direct physiological limit). Recent work has shown that environmental heat stress has already reduced the labor capacity in the tropics and mid-latitudes during peak months of heat stress by 10%, and another 10% decrease is projected by 2050 with much larger decreases further into the future (NRC 2013).
Higher Heat effects on Biodiversity
As the planet’s oceans and rivers warm, increased heat could pose a grave threat to the fish populations the world depends on by the end of this century. Three billion people depend on fish and seafood as their main source of protein (WWF 2021). Among the species at risk are some of the most commercially important species on Earth — Atlantic cod, Alaska pollock and sockeye salmon, and sport fishing favorites like swordfish, barracuda and brown trout. In fact, 60% of the fish species examined could struggle to reproduce in their current habitat ranges by the year 2100 if the climate crisis continues unchecked (Dahlke et al 2020).
Higher Heat effects on invasive species
Bark beetles are a natural part of forested ecosystems, and infestations are a regular force of natural change. In the last two decades, though, the bark beetle infestations that have occurred across large areas of North America have been the largest and most severe in recorded history, killing millions of trees across millions of hectares of forest from Alaska to southern California. Climate change is thought to have played a significant role in these recent outbreaks by maintaining temperatures above a threshold that would normally lead to cold-induced mortality.
Over 30% more ponderosa pines died in the Sierra during last decade’s drought due to the hastened rate of beetle development, who mature faster in higher temperatures, shortening the time it takes to new generations. This will worsen tree deaths — already California has lost 163 million trees since 2010 due to a combination of beetles and drought. This makes it more likely trees won’t grow back as well, these areas will increasingly become inhabited by shrubs and grasslands (Robbins 2021)
References
Dahlke FT, Wohlrab S, Butzin M et al (2020) Thermal bottlenecks in the life cycle define climate vulnerability of fish. Science 369: 65-70
Robbins ZJ (2021) Warming increased bark beetle-induced tree mortality by 30% during an extreme drought in California. Global Change Biology.
SD (2010) Global Warming: Future Temperatures Could Exceed Livable Limits, Researchers Find. ScienceDaily.
McMichael A et al (2010) Climate change: Heat, health, and longer horizons. Proceedings of the National Academies of Science.
NRC. 2013. Abrupt Impacts of Climate Change: Anticipating surprises. National Research Council, National Academies of Sciences press.
Sherwood S et al (2010) .An adaptability limit to climate change due to heat stress. Proceedings of the National Academies of Science.
WWF (2021) Sustainable seafood overview. World Wildlife Fund.