Research press release


Nature Climate Change

Working up a sweat



従来の湿度に関連した研究の大部分は、気温の持続的上昇ではなく、酷暑と関連した影響に注目していた。今回、J Dunneたちは、空気中の湿度によってほぼ決まる湿球温度の歴史的解析とモデルによる予測に対して、環境熱ストレスを受けている個人が持続的労働を安全に遂行する能力に関する業界と軍隊のガイドラインを組み合わせた。その結果、過去数十年間に、環境熱ストレスによってピーク月の労働能力が90%に低下し、その後も低下が進み、2050年にはピーク月の労働能力が80%に低下するという予測を示した。このモデルで考慮されたCO2排出量が最大となるシナリオでは、ピーク月の労働能力が2200年までに40%未満に低下するとされる。さらに、Dunneたちは、この極端なシナリオでは、熱帯域と中緯度域の人々の大部分が、ピーク月に極度の熱ストレスにさらされて、広範な地域で安全な労働ができなくなり、米国のロッキー山脈の東側などの中緯度域での環境熱ストレスが、世界で最も高温の地域だけで経験されているレベルに達することも報告している。


Climate warming over the past few decades has led to an increase in humidity, and work published in Nature Climate Change suggests that this has reduced people’s working capacity to 90% in peak months. The report predicts that this reduction in working capacity will be greater under future warming scenarios, with most tropical and mid-latitude regions expected to experience extreme heat stress, as well as humidity, by 2200.

An important aspect of greenhouse-gas-induced warming is a global increase in absolute humidity. This increase in humidity is thought to limit human activity in tropical and mid-latitudes during peak months of heat stress.

Most research related to moist temperature to date has focused on effects associated with heat waves, rather than sustained temperature increases. John Dunne and colleagues combine historical analysis of wet bulb temperature - which is largely determined by the amount of moisture in the air - and model projections with industrial and military guidelines for an individual’s capacity to safely perform sustained labour under environmental heat stress. They estimate that environmental heat stress has reduced labour capacity to 90% in peak months over the past few decades and project that there will be a further reduction to 80% in peak months by 2050. Under the highest CO2 scenario considered by the model, labour capacity would be reduced to less than 40% by 2200 in peak months. They report that this extreme scenario would expose most of the present tropical and mid-latitude populations to extreme heat stress in peak months, prohibit any safe labour in large areas and expose mid-latitude regions, such as the US east of the Rockies, to a level of environmental heat stress that is currently only experienced in the hottest regions of the world.

The authors emphasize, however, that these projections don’t include information about climate sensitivity, climate warming patterns, CO2 emissions, future population distributions and technological and societal change.

doi: 10.1038/nclimate1827


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