(The research achievement has been published on RGC YouTube Chanel on 22 Jul 2018)
Each of the three years from 2014 to 2016 broke the global air temperature record, and 2017 will also turn out to be one of the hottest years ever. To predict how humans will be affected by climate change, geographers and climatologists led by Professor David Chen Yongqin from the Department of Geography and Resource Management at The Chinese University of Hong Kong (CUHK) and Dr Li Jianfeng from the Department of Geography at Hong Kong Baptist University (HKBU) studied the apparent temperature (AP), the temperature equivalent perceived by humans. They found that AP increased faster than air temperature (AT) over land in the past few decades, especially in the low latitude areas, and the rise is expected to continue in the future. This finding was recently published in Nature Climate Change.
Scientists have developed and used Global Climate Models (GCMs) to simulate the global climate and make projections of future AT and other climatic variables under different carbon emission scenarios in the 21st century. However, GCMs do not directly project how the change of other climatic factors, such as humidity and wind, affects human perception.
Professor Chen remarked, “Among the extensive and far-reaching impacts of global warming, human health and labour productivity are most directly affected by thermal discomfort and heat-related morbidity and mortality. Our study of the faster increases in apparent temperature has produced important findings for this kind of climate change impact assessment, providing a strong scientific support for more stringent and effective climate change mitigation efforts to combat global warming.”
Dr Li said the latest research findings give a better understanding of changes in human-perceived equivalent temperature, and indicate global warming has stronger long-term impacts on human beings under both extreme and non-extreme weather conditions, suggesting that climate change adaptation cannot just focus on heat wave events, but should be extended to the whole range of effects of temperature increases. The team will continue to explore the related issues to enhance the scientific knowledge.
The research team used four reanalysis datasets of the past climate and outputs from seven GCMs to estimate the human-perceived equivalent temperature AP, from AT, humidity and wind. Findings showed that the global land average AP increased 0.04℃ per decade faster than AT before 2005, because of the concurrent increases in AT and humidity. This trend was projected to increase to 0.06 ℃per decade and 0.17℃per decade under Representative Concentration Pathway 4.5 scenario (RCP4.5) and RCP8.5, respectively, and reduce to 0.02℃ per decade under RCP2.6. The faster increases in AP are more significant in low latitude areas (tropical and sub-tropical regions) than the middle and high latitude areas. Study also indicated that the number of days with extremely apparent temperature will substantially increase in 2081 to 2100 compared to the period between 1981 and 2000, mainly due to the remarkable increase in the frequency of extremely hot days in summer.
Taken together, a key conclusion is that the world, as perceived by human beings, will become hotter than that just indicated by air temperature under global warming. This conclusion clearly implies that cities and communities, especially those located at tropical and sub-tropical regions like Hong Kong, will face bigger threats from hot weather and therefore greater efforts for climate change mitigation and adaptation are vital and urgent.
In this study, Professor Chen and Dr Li collaborated with AXA Professor Gabriel Lau Ngar-Cheung from the Department of Geography and Resource Management at CUHK, and Professor Thian Yew Gan from the Department of Civil and Environmental Engineering at the University of Alberta in Canada.
研究團隊利用四個歷史氣候的再分析數據集，以及七個全球氣候模式的模擬結果，計算和模擬體感溫度的變化和趨勢，發現2005年前全球陸地平均體感溫度的增速較實際溫度增速每10年快0.04℃，原因是氣溫上升的同時濕度亦增加，人體感受到的熱力因而增加。預測未來在高、中、低三種碳排放情境（即所謂「代表濃度路徑」）下，體感溫度上升將分別較實際溫度每十年快0.17℃（RCP8.5）、0.06℃（RCP4.5）和0.02℃（RCP2.6），低緯度地區 (即熱帶或亞熱帶地區) 體感溫度上升亦較中高緯度地區明顯。研究亦顯示於2081-2100年出現極端體感溫度的日數將會較1981-2000年顯著增加，主要是夏季出現極端熱的頻率大幅上升。