High temperatures beyond the limit of survival have already occurred, but this is just the beginning

Summer is becoming increasingly unbearable.

Since mid-June this year, extreme high temperatures have continued to occur, and the temperatures in different cities across the country have successively broken the highest records of the same time in previous years. Especially since the Great Heat, cities with the highest temperature exceeding 40°C have frequently appeared. High temperatures are not only occurring in China. Looking at the northern hemisphere, the United States has continued to ignite forest fires, and 510 people have died in Spain due to high temperatures in a week. At the same time, Finland and Norway, which are close to the Arctic Circle, have also seen high temperatures of nearly 34°C.

How far has the Earth's "fever" progressed? Do scientists have any solutions? Will our descendants still be able to see the summer with breeze and cicadas chirping, and have the same sweet memories of summer as we do?

The extreme high temperature that humans can withstand has already appeared

Let me first state the conclusion: the earth has indeed been running a fever in recent years, and it has become increasingly uninhabitable for human beings.

Studies have shown that high temperatures that exceed the human tolerance range have begun to appear [1]. However, the temperature used to measure the "human limit" is not the temperature that we get from daily weather forecasts (the temperature of the air in a louvered box at a height of 1.5 meters), but the wet-bulb temperature .

People are facing the test of high temperature | Weibo @Shanghai Weather

Compared with air temperature, wet-bulb temperature is more closely related to human vital signs.

The definition of wet bulb temperature is the temperature that a piece of air reaches when it is saturated (relative humidity reaches 100%) after humidification. In other words, it is the lowest temperature that the current environment can reach simply by evaporating water . Therefore, wet bulb temperature is closely related to relative humidity.

The normal human body temperature is about 37°C, and the skin temperature is maintained at about 35°C. In a high temperature environment, the human body mainly regulates its body temperature through sweating. However, when the humidity of the environment is high, this heat dissipation pathway is blocked, and people will feel "stifling heat". The human body's own cooling function has a certain threshold. When the wet-bulb temperature reaches 35°C, even healthy people cannot dissipate heat normally , resulting in a great health risk due to the increase in core body temperature, and even death[2].

Research in 2020 showed that wet-bulb temperatures in some subtropical coastal areas have reached a lethal 35 °C, and the frequency of such extreme hot and humid weather has doubled in nearly four decades [1], while scientists had originally thought that this would take at least several decades to occur.

The recent high temperatures in Zhejiang, Fujian, and Guangdong are usually accompanied by high humidity. In many cases, the temperature reached 40°C with 60% relative humidity, or the temperature reached 36°C with 80% relative humidity. In this case, the wet bulb temperature reached 33°C, which is very close to the lethal wet bulb temperature . It is very dangerous to carry out any outdoor activities for a long time in such an environment, which is why there were frequent incidents of outdoor workers fainting due to heat stroke in the high temperature during that period.

Wet-bulb temperature corresponding to different relative humidity and air temperature conditions (wet-bulb temperature is calculated according to Stull (2011)[3]) | Self-made figure

In fact, the heat wave that swept the world this summer arrived in India and Pakistan as early as March, bringing the hottest March since 1901 (maximum temperature exceeded 40°C). Since May, the United States, Europe and China have also been hit by large-scale heat waves.

At its core, climate change caused by global warming is the main cause of this phenomenon. In the past sixty years (1960-2018), the highest recorded regional high temperature events in China occurred in the summers of 2003, 2013, and 2017, with 2013 being the worst (highest temperature and longest duration) [4]. Studies have shown that the extreme degree of heat waves (temperature, duration, and impact range) increases almost linearly with the trend of global warming . The frequency of heat wave events caused by a global warming of 2°C (compared to pre-industrial times) will be twice as high as that caused by a global warming of 1.5°C [4].

If humans cannot slow the pace of global warming, summers will become hotter and more "invincible" in the foreseeable future.

Extreme climate, high temperature is only the first step

The continued high temperature directly tests human adaptability.

In addition to the obvious physiological risks, a review article based on previous related studies around the world shows that high temperatures can also have a negative impact on people's mental health [6]. Researchers found that when a heat wave occurs, the incidence of mental health-related diseases will increase by 0.9% for every 1°C increase in temperature, and the mortality rate will increase by 2.2%. Low-income groups are at a higher risk of mental illness caused by high temperatures due to the relative lack of sufficient cooling conditions.

The impact of continued high temperatures on agriculture cannot be ignored. Long-term drought and high temperatures will affect the growth of crops and cause insect plagues. In order to ensure the harvest, the combined effect of various factors will eventually cause the prices of grain, vegetables and fruits to continue to rise for a long time. This is undoubtedly a double whammy for the poor.

In the face of extremely hot weather, the demand for cooling is rapidly increasing, and humans have to consume more energy. Clean energy itself accounts for a limited proportion, and high temperatures and droughts have hindered wind and hydropower generation. Humans can only burn more fossil fuels, which will further increase greenhouse gas emissions. This vicious cycle will exacerbate global warming and make summers hotter and hotter.

Extreme heat is our most direct experience of climate change, but the real threat to the survival of human populations is the secondary disasters brought about by climate change . Extreme heat is usually accompanied by drought and can cause forest fires around the world. Not only does it cause serious local air pollution and force a large number of residents to evacuate, it can also seriously damage the forest ecosystem on which humans depend for survival. There is a high probability of heavy rainfall before and after extreme heat, leading to floods and waterlogging disasters.

According to statistics[7], in southern, northwestern and northeastern China, the frequency of this type of complex flood and heat wave sequence occurring continuously within a week has increased five to ten times since 2000. In the densely populated Yangtze and Huaihe River basins, the frequency of typhoon-related flood and heat wave events occurring within a week has increased by as much as ten times. This continuous extreme weather not only causes casualties and economic losses, but also increases the difficulty of post-disaster rescue and reconstruction.

Although there are currently no areas in China prone to deadly heat waves, climate change is coming faster than expected. According to a 2020 McKinsey report, by 2030, 10 million to 45 million people in China may face the threat of extreme heat and deadly heat waves, and by 2050, this number may rise to 110 million to 250 million [8].

What are scientists doing?

Faced with the climate challenge that has already arrived, scientists are racing against time to find the causes and solutions to global warming.

Every six years or so, the Intergovernmental Panel on Climate Change (IPCC), an intergovernmental organization under the United Nations, convenes thousands of scientists from around the world to review the scientific literature published during this period and write a report. The sixth IPCC report released this year shows[9] that the impact of human activities has significantly caused the temperature of the atmosphere, oceans and land surface to rise, and the rate of warming is unprecedented in the past two thousand years.

Since 1950, extreme high temperature weather (including heat waves) has become more frequent and intense in most land areas. The main factor causing global warming is greenhouse gas emissions, led by carbon dioxide and methane. For the picture of sustainable development of mankind, we must first try to slow down the rate of global warming by reducing emissions.

History of global temperature change and causes of recent warming. (a) Global surface temperature changes reconstructed from paleoclimate archives (b) Changes in global surface temperature over the past 170 years | IPCC, 2021: Summary for Policymakers

According to model predictions[10], if humans want to keep global warming below 2°C, global greenhouse gas emissions need to peak between 2020 and 2025 (at the latest) . The report of the IPCC Working Group III shows[10] that during the period 2010-2019, total net anthropogenic greenhouse gas emissions continued to rise, with average emissions higher than in any previous decade, although the growth rate was lower than in the previous decade (2000-2009).

Under the approaching climate challenge, countries have also begun to take emergency measures to survive the bitter summer. On August 1, in order to save energy, in Spain, where the temperature once soared to 47°C, the government required that the air-conditioning temperature of enterprises, restaurants, museums and other places should not be lower than 27 degrees Celsius, and doors and windows should be closed when the air-conditioning is turned on; in order to protect outdoor workers, Guangdong, one of the hottest provinces in my country in summer, also stipulates that outdoor work should be stopped on the same day when the maximum daily temperature reaches above 39°C. At the same time, some countries are trying to build "sponge cities" that adapt to extreme climates, and better cope with the extreme heavy precipitation caused by global warming by increasing the green space rate and using permeable paving.

However, these measures are only stopgap measures taken by humans to maintain their daily lives under climate change. To slow down the pace of global warming, we need the wisdom, consensus, and cooperation of all mankind. This is not an easy task, but it is the most important thing for our species . Because for the earth, humans are no different from fungi, birds, and trees. Even if the temperature continues to rise and tsunamis engulf coastal cities, the earth will continue to exist. The only ones who are truly hovering at the crossroads of survival are us .

References

[1] Raymond, Colin, Tom Matthews, and Radley M. Horton. "The emergence of heat and humidity too severe for human tolerance." Science Advances 6.19 (2020): eaaw1838.

[2] Schär, C. The worst heat waves to come. Nature Clim Change 6, 128–129 (2016). https://doi.org/10.1038/nclimate2864

[3]Stull, Roland. "Wet-bulb temperature from relative humidity and air temperature." Journal of applied meteorology and climatology 50.11 (2011): 2267-2269.

[4]Wang, Jun, and Zhongwei Yan. "Rapid rises in the magnitude and risk of extreme regional heat wave events in China." Weather and Climate Extremes 34 (2021): 100379.

[5]Sun, Y., Hu, T., & Zhang, X. (2018). Substantial increase in heat wave risks in China in a future warmer world. Earth's Future, 6(11), 1528-1538.

[6] Liu, Jingwen, Blesson M. Varghese, Alana Hansen, Jianjun Xiang, Ying Zhang, Keith Dear, Michelle Gourley et al. "Is there an association between hot weather and poor mental health outcomes? A systematic review and meta-analysis." Environment international 153 (2021): 106533.

[7]Chen, Y., Liao, Z., Shi, Y., Tian, ​​Y., & Zhai, P. (2021). Detectable increases in sequential flood-heatwave events across China during 1961–2018. Geophysical Research Letters, 48, e2021GL092549. https://doi.org/10.1029/2021GL092549

[8] McKinsey Global Institute (MGI). Climate Risk and Response: Physical Hazards and Socioeconomic Impacts [EB/OL]. [2020-06-12]. https://www.mckinsey.com.cn/

[9]IPCC, 2021: Summary for policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, SL Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, MI Gomis, M. Huang, K. Leitzell, E. Lonnoy, JBR Matthews, TK Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32, doi:10.1017/9781009157896.001.

[10] IPCC, 2022: Summary for policymakers. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [PR Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001

Author: Judy

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