| 英文摘要: | A human body may be able to adapt to extremes of dry-bulb temperature (commonly referred to as simply temperature) through perspiration and associated evaporative cooling provided that the wet-bulb temperature (a combined measure of temperature and humidity or degree of ‘mugginess’) remains below a threshold of 35 °C. (ref. 1). This threshold defines a limit of survivability for a fit human under well-ventilated outdoor conditions and is lower for most people. We project using an ensemble of high-resolution regional climate model simulations that extremes of wet-bulb temperature in the region around the Arabian Gulf are likely to approach and exceed this critical threshold under the business-as-usual scenario of future greenhouse gas concentrations. Our results expose a specific regional hotspot where climate change, in the absence of significant mitigation, is likely to severely impact human habitability in the future. The geologic formations beneath and around the Arabian Gulf (hereafter referred to as the Gulf) in Southwest Asia, commonly referred to as the Middle East, are a major source for the oil and gas consumed locally and around the world, contributing greatly to the past and current emissions of carbon dioxide2. Here, we show that by the end of the century certain population centres in the same region are likely to experience temperature levels that are intolerable to humans owing to the consequences of increasing concentrations of anthropogenic greenhouse gases (GHGs). The 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) presents substantial evidence that increasing anthropogenic GHG concentrations are responsible for much of Earth’s warming in recent decades3. Although observations and model simulations largely support this global climate change hypothesis, more research efforts are needed to improve understanding of impacts at regional and local scales. Some important limitations to the accuracy of global climate model (GCM) projections of these impacts stem from the lack of sufficient resolution needed to resolve regional processes and understand societal impacts; and the inadequate treatment of physical processes of regional importance4, 5. To investigate dangers to human health of extreme heat and humidity in Southwest Asia, we apply a regional climate model (RCM) at a 25-km grid spacing specifically customized for the region6, 7, 8, 9 forced by three IPCC GCMs objectively selected based on performance (see Supplementary Methods). By conducting high-resolution RCM simulations, we resolve approximately 30 grid-points for each GCM grid-point, allowing a more detailed representation of topography, coastlines, extreme climatic events, and physical processes. We consider both dry-bulb temperature (T) and wet-bulb temperature (TW), specifically their daily maxima averaged over 6 h, denoted by Tmax and TWmax, respectively. Whereas the general public can easily relate to the concept of T, TW is not a widely used and understood concept. It is the temperature an air parcel would attain if cooled at constant pressure by evaporating water within it until saturation10. It is a combined measure of temperature and humidity, or ‘mugginess’. Like all living species, human survival is partially a function of the environmental temperature. 35 °C is the threshold value of TW beyond which any exposure for more than six hours would probably be intolerable even for the fittest of humans, resulting in hyperthermia. In current climate, TW rarely exceeds 31 °C (ref. 1). Although other dry-bulb temperature and combined empirical temperature and humidity indices have been used to investigate the impacts of climate change on heat stress11, 12, 13, 14, 15, TW provides a physically based relationship to the human body’s core temperature. For extreme temperature, we arbitrarily select 60 °C, a value close to the highest temperature ever reported on Earth16, 17. In dry heat conditions, the human body is at high risk of heat stroke at temperatures well below 60 °C if not well hydrated and if exposed to the sun. In addition, when T approaches such extremes, much machinery designed for the current climate may malfunction. For example, aircraft may not operate properly during takeoff and landing, and rail lines can buckle at extreme temperatures, even at temperatures around 40 °C. Under recent climate conditions (1976–2005) with historical GHG concentrations18, the ensemble average of the largest TWmax event exceeds 31 °C, primarily in the Gulf and surrounding coastal regions (Fig. 1). These regions are located in low-elevation areas close to sea level allowing for high T, and near the coast allowing for high humidity. Interior desert regions have lower values of TW and TWmax owing to drier air. Although the 35 °C threshold is approached in many locations, it is not exceeded anywhere in the domain. In contrast, the ensemble average of the largest Tmax events exhibits values exceeding 50 °C in some interior desert regions and in coastal areas, but relatively low values over the Gulf and Red Sea. These severe heat-related conditions located in relatively low areas located near water bodies are consistent with projected heat-wave conditions in southern Europe and Mediterranean coasts13.
| http://www.nature.com/nclimate/journal/v6/n2/full/nclimate2833.html
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