As this century progresses, rising nighttime temperatures could lead to an average annual sleep loss of about 16 hours per person. Children, particularly in areas with limited cooling options, are expected to be the most affected. This is based on an analysis published in Nature Sustainability, which outlines a troubling sequence of events linking warm bedrooms to reduced future earnings.
Hotter nights reduce sleep duration. Insufficient sleep during childhood can impair cognitive development, which in turn affects lifetime earnings. On a global scale, under a high-emissions scenario, the cost of lost sleep could amount to trillions of dollars, disproportionately impacting countries that have contributed the least to climate change. While individual effects may be small, the cumulative impact exacerbates disparities between wealthy and poorer regions.
From a hot night to a smaller paycheck
Research led by Bowen Chu and his team at Nanjing University connects three previously separate findings: the impact of temperature on sleep length, the effect of childhood sleep on IQ, and the correlation between IQ and economic productivity over a lifetime. By linking these elements, the study offers a projection of how climate change could influence human capital and future earning potential on a broad scale.
Compared to a 2001–2010 baseline, and assuming no adaptation, sleep loss may reach 16.4 hours per person annually by the 2100s under the highest emissions pathway, with global temperatures rising by 2.4°C by 2060. The most significant impacts are expected in southern and eastern Africa and southern and eastern Asia.
An accompanying commentary explores the downstream effects. IQ loss per person might average 0.026 points in high-income countries and 0.058 points in lower-income ones. Though these figures may appear minor individually, they translate into a global economic loss of approximately $2.86 trillion by the 2100s. The research underscores the severe consequences of a warming planet.
This study attempts to quantify the cascading effects that will occur if efforts to mitigate global warming are not implemented. It is not a definitive prediction.
Why heat robs you of rest
For sleep to occur, core body temperature must decrease, reaching its lowest point early in the morning in sync with circadian rhythms. A warm environment obstructs this cooling process, hindering the brain’s ability to reach deep, restorative stages of sleep. Michelle Drerup, a sleep specialist at the Cleveland Clinic, notes that “Heat is a huge disruptor for REM sleep.”
The impact of heat on sleep is not uniform. Studies consistently show that older adults, women, individuals in lower-income countries, and those living in already hot climates experience the most sleep loss as nights get warmer. These groups typically have fewer resources to manage the heat.
The cooling trap
While air conditioning is a straightforward solution, the study’s assumption of “no adaptation” reveals complexities. AC cools rooms but often relies on electricity from fossil fuels, contributing to emissions. Additionally, the refrigerants in many units are potent greenhouse gases. Moreover, AC is least accessible in the hotter, lower-income regions that are most vulnerable.
The core finding highlights that while adaptation strategies are available, their distribution is uneven. The most effective and universal solution remains reducing atmospheric CO2 levels. The projected 16-hour sleep loss is linked to a high-emissions future; lower-emission pathways can mitigate this impact. Thus, the choice to reduce emissions can influence the scale of harm.
What You Can Do
For a cooler night’s sleep, starting tonight:
- Aim cool. Experts recommend a bedroom temperature around 65°F, with an acceptable range between 60 and 68°F.
- Block the day’s heat. Close curtains and blinds against direct sunlight and keep windows shut when outside temperatures are higher. Sunlight raises room temperature and inhibits melatonin production.
- Flush heat at night. Once the outside air cools, open windows and create cross-ventilation using fans. A bowl of ice in front of a fan can provide a simple cooling effect.
- Take a warm shower one to two hours before bed. Despite seeming counterintuitive, warming the body can trigger blood-vessel dilation, aiding in heat dissipation. A 2019 meta-analysis suggests a 10-minute warm bath or shower at 104–108°F can help induce sleep more quickly. In extreme heat, a lukewarm shower is more tolerable and still beneficial.
- Go breathable, and go low. Opt for lightweight cotton bedding and sleepwear to avoid trapped heat. Sleeping on a lower floor or closer to the ground can also help.
For your home and your footprint:
- Prioritize fans, shading, and insulation over air conditioning, and ensure any AC used is efficient, properly maintained, and adjusted as temperatures allow.
- Utilize low-tech cooling methods during milder weather to conserve energy for more extreme heat conditions.
In your community:
- Advocate for community cooling centers, urban tree canopies, and heat-island reduction efforts to support those without home cooling options, as identified by the research.
- Focus on reducing emissions to prevent the high-warming scenario, addressing both the root cause of heat and its impact on sleep.
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