10 January 2018

CUHK and HKBU discover the elevated increases in human-perceived temperature under climate change



Each of the three years from 2014 to 2016 broke the global average 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 change in apparent temperature (AP), the temperature equivalent perceived by humans, under climate change over the past few decades. They found that AP increased faster than air temperature (AT) over land, 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 changes of other climatic factors, such as humidity and wind, affect 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 0.04oC per decade faster than AT before 2005, because of the concurrent increases in AT and humidity. This trend was projected to increase to 0.17oC per decade and 0.06oC per decade under the Representative Concentration Pathway (RCP) 8.5 and RCP 4.5 scenarios, respectively, and reduce to 0.02oC per decade under RCP2.6 scenario. 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 Professor Gabriel Lau Ngar-Cheung, Director of the Institute of Environment, Energy and Sustainability and AXA Professor of Geography and Resource Management of CUHK, and Professor Thian Yew Gan from the Department of Civil and Environmental Engineering at the University of Alberta in Canada. 

About Professor David Chen Yongqin

Professor David Chen joined the Department of Geography and Resource Management at CUHK in 1997, and is the Leader of the China Environment Programme, Institute of Environment, Energy and Sustainability at The Chinese University of Hong Kong. He obtained his Bachelor’s (1984) and Master’s (1987) degrees from Zhongshan University, and Ph.D. (1996) from the University of Georgia, USA. His research and teaching areas include hydrology and water resources management, meteorology and climatology, environmental assessment and modeling, and regional development. In recent years, his research activities have focused on the impacts of global and regional climate change, hydrologic changes and low-flow hydrology in the Pearl River basin, urban water management in Hong Kong and strategic environmental assessment in China. He has published over 100 papers in these areas in international and Chinese journals, as well as book volumes. He has been active in serving in various professional societies and government advisory committees, including as President of the Professional Association for China’s Environment and member of the Strategic Advisory Committee, Hong Kong Observatory etc.

About Dr Li Jianfeng

Dr Li Jianfeng is an assistant professor in the Department of Geography, and the deputy director of the Centre for Geo-computation Studies of HKBU. His major research interests include hydroclimatology, environmental change, and water hazards, focusing on climate change impacts on hydrological processes and the environment especially hydrological and climatic extremes. He is the associate editor of Hydrological Processes, an international journal in hydrology, and has been active in serving in various professional communities. Dr Li obtained his Bachelor’s and Master’s degrees from the School of Geography and Planning at Sun Yat-sen University, and completed his Ph.D. in Geography and Resource Management from CUHK. He studied in the Department of Civil and Environmental Engineering in Princeton University, and at Land and Water in the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia as a visiting researcher. Dr Li is a recipient of the Heywood Young Scientist Award of the Hong Kong Meteorological Society, the Postgraduate Research Output Award of CUHK, and the Endeavour Research Fellowship of Australian Government Department of Education, etc.

(From left) Professor David Chen Yongqin and Professor Gabriel Lau Ngar-Cheung from CUHK, and Dr Li Jianfeng from HKBU
(From left) Professor David Chen Yongqin and Professor Gabriel Lau Ngar-Cheung from CUHK, and Dr Li Jianfeng from HKBU

Spatial distribution of the projected changes in AP-AT under RCP8.5, shows that AP is 3 to 6 degrees Celsius higher than AT in most low latitude regions.
Spatial distribution of the projected changes in AP-AT under RCP8.5, shows that AP is 3 to 6 degrees Celsius higher than AT in most low latitude regions.

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