GEOG Scholar discovered Human-perceived Temperature is Rising Faster than Actual Air Temperature under Climate Change

2018-01-23

To predict how humans will be affected by climate change, geographers and climatologists led by Dr. Li Jianfeng from Geography Department, HKBU and Prof. David Chen Yongqin from Department of Geography and Resource Management, The Chinese University of Hong Kong (CUHK) 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.

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. The 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, Dr. Li and Prof. Chen collaborated with AXA Prof. Gabriel Lau Ngar-Cheung from the Department of Geography and Resource Management at CUHK, and Prof. Thian Yew Gan from the Department of Civil and Environmental Engineering at the University of Alberta in Canada.