BANGKOK, April 12 (Thomson Reuters Foundation) - In 2016, the Earth experienced its hottest year since the 1880s when modern records began, marking the third consecutive year of record-high temperatures. Less than four months into 2017, parts of Australia and India are already in the throes of heat waves.
While sunny skies may be synonymous with summer fun in some parts of the world, too much heat can be fatal.
It is estimated that between 15,000 and 19,000 people died during France's heat wave of 2003, while the United States' Centers for Disease Control and Prevention (CDC) said some 600 Americans died every year from exposure to extreme heat between 1999 and 2010.
The Thomson Reuters Foundation spoke to half a dozen climate scientists to understand what rising temperatures mean for human health. Here are some key facts and figures:
* Hotter days and nights, and heat waves will become more common. Multiple studies have found that heat waves are happening more frequently, while cold spells declined in urban areas in the last 40 years.
* Extreme heat can cause heat-related illnesses, such as heat stroke and exhaustion, and increase mortality. It can also exacerbate existing health conditions. Heat stress occurs when the body absorbs more heat than is tolerable.
* The total number of days on which heat reaches "health-threatening levels" will rise rapidly over the next several decades, noted one study by the Institute for Social and Environmental Transition-International (ISET-International) and the National Center for Atmospheric Research (NCAR). Another recent study by British researchers warned that conditions that have challenged and overwhelmed people in the most heat-stressed regions could become "much more frequent", while population growth will make things worse.
* Urban centres in the developing world will be hit hardest. They tend to be hotter than rural areas due to factors including population density, pollution from industrial activities, and the presence of buildings and machinery that create heat. This "urban heat island" effect is well known, but will worsen with rising temperatures.
* New populations will become heat-stressed while those already exposed to dangerous levels of heat will be subject to harmful conditions more often, scientists say.
* With a temperature rise of 1.5 degrees Celsius, cities in China, India, Bangladesh, Ivory Coast, Nigeria, Vietnam and Myanmar will regularly start to experience heat stress, according to the UK study.
* If global temperature rise hits 2.7 degrees Celsius, Tokyo, Beijing and Manila will also be affected, while a 4 degree rise would see New York and Rio de Janeiro join the club.
* Southeast Asia faces a 16 percent loss of labour capacity in the next three decades due to heat stress, said a study by risk consultancy Verisk Maplecroft. A separate report by the U.N. Development Programme, International Labour Organisation and the Climate Vulnerable Forum said emerging economies could lose as much as 10 percent of their daytime working hours due to searing temperatures.
* The World Health Organization (WHO) has estimated that without adaptation measures, there will be nearly 65,000 additional deaths annually among people over 65 due to heat exposure in 2030, with the greatest impacts in Asia-Pacific.
* Humidity levels and night-time temperatures play an important - but often neglected - role, because they influence the body's ability to cool down. Daytime peak temperatures can be dealt with partially by seeking shade and sweating, but it is harder to act at night.
* According to the WHO, ideal room temperature should be below 32 degrees Celsius during the day and under 24 degrees Celsius at night.
* Rice, Asia's staple food, is highly susceptible to heat stress, with yields plummeting if temperatures are above 35 degrees Celsius for 10 days during the reproductive stage. Sources: NASA, CDC, ISET-International, ISET-Pakistan, Proceedings of the National Academy of Sciences of the United States of America (PNAS), NCAR, WHO, Verisk Maplecroft, Climate Vulnerable Forum, International Centre for Climate Change and Development (Reporting by Thin Lei Win, editing by Megan Rowling; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women’s rights, corruption and climate change. Visit www.trust.org)