Scientists warn of escalating heatwave risks due to global warming
The record breaking humid heat wave that hit east and north India; Bangladesh; Laos and Thailand in April were made at least 30 times more likely by climate change, a rapid attribution analysis said on Wednesday.
The analysis by an international team of scientists with the World Weather Attribution group said a highly vulnerable population was subjected to a deadly combination of high heat and humidity which amplified the impacts in early summer this year.
Large populations across South Asia during a 4-day period between April 17 and 20 were exposed to a heat index or ‘feels like’ temperature of over 41 degree C and some areas particularly in Laos recorded heat index of over 54 degree C which can be deadly, scientists said. WWA’s report coincided with a statement issued by World Meteorological Organisation on Wednesday cautioning that there is a 66% likelihood that the annual average global temperature between 2023 and 2027 will be more than 1.5 degree C above pre-industrial levels for at least one year.
India and Pakistan also experienced a severe heat spell last March and April. The 2022 heatwave is estimated to have led to around 90 deaths across India and Pakistan; triggered an extreme Glacial Lake Outburst Flood in northern Pakistan; forest fires in India; reduced India’s wheat crop yields; power outages that impacted millions of people. WWA scientists had said the climate crisis had made such an event 30 times more likely. On Wednesday they said while India experienced a dry heat episode last year, this year it was in more humid, coastal regions of the country.
This April, parts of south and southeast Asia experienced an intense heatwave spell, with record-breaking temperatures that passed 44 degree C over east India; 42 degree C in Laos and 45 degree C in Thailand. The heat caused widespread hospitalisations, damaged roads, sparked fires and led to school closures. The number of deaths remains unknown, scientists said.
In Bangladesh, Dhaka observed the highest maximum temperature recorded in decades of 40.6 degree C on April 15. In India, several northern and eastern cities recorded maximum temperatures above 44 degree C on April 18. Thailand recorded its highest ever temperature of 45.4 degree C on April 15 in the city of Tak. The Sainyabuli province in Lao PDR reported 42.9 degree C on April 19 as its all-time national temperature record. Vientiane, the capital of Lao PDR, recorded 41.4 degree C on April 15, the hottest day ever for the capital. On the same day, Luan Prabang in Lao PDR reported 42.7 degree C.
The analysis states that there was a sudden surge in heat strokes, electricity demand, around 13 casualties and about 50-60 hospitalisations due to heat stroke were reported in Navi Mumbai, Maharashtra on April 16. Other sources mention 650 hospitalisations. Casualties were also reported from Thailand. “The true cost to human lives will only be known months after the event. In India, in the states of West Bengal, Tripura and Odisha, schools closed three weeks earlier than planned due to the heat. In addition, a large number of forest fires occurred during the same time in India, Thailand and Lao PDR,” the analysis said on Wednesday.
Scientists from India, Thailand, France, Australia, Denmark, Germany, Kenya, the Netherlands, the US and the United Kingdom collaborated to assess how the climate crisis made such a heat spell in April more likely. Using peer-reviewed methods, available datasets, scientists analysed how climate change altered the likelihood and intensity of the 4-day April heatwave event. They measured the impact of the heat spell as a heat index which integrates temperature and humidity. The analysis released on Wednesday has not yet been peer reviewed but is expected to go through peer review soon.
Due to the high humidity conditions during the heatwave, heat index values are higher than the actual temperatures. The team excluded the dry, semi-arid region that runs parallel to the Western Ghats where humidity is low in the pre-monsoon season for a clear assessment. The heat index values found by the team exceeded the threshold considered as “dangerous” (41 degree C) over the large parts of the South Asian regions studied this year. In a few areas, it was in “extremely dangerous” category (above 54 degree C) under which the body temperature is difficult to maintain, scientists said.
To decipher the influence of climate change on extreme heat, based on the 1.2 degree C warming in average global temperatures, the team combined observations and models which shows there is an increase in likelihood of such an event to occur by at least a factor of 30 over India and Bangladesh due to current warming levels. At the same time, a heatwave with a chance of occurrence of 20% in any given year over India and Bangladesh is now about 2 degree C hotter in terms of heat index than it would be without global warming. In India and Bangladesh, the likelihood of this April’s event reoccurring would increase by about a factor of 3 between now and reaching 2 degree C global warming, meaning that such an event could be expected every 1-2 years, the analysis said.
The impacts of climate change on exacerbating heat are not uniform and vary greatly based on the region, scientists said. “Last year’s spring heat spell was largely a dry event. Its impact on crops was more but impact on human health was comparatively less. This year however the impact on health was more because it was humid heat. These regions are continuing to see very high temperatures. We are seeing an increase in both kinds of heat events- prolonged dry heat and extreme humid heat,” said Mariam Zachariah from the Grantham Institute, Imperial College London, UK who is a co-author of the analysis during a briefing.
“Frequency and severity of heat waves have been increasing over the country over the past few decades. Due to climate change, the water vapour holding capacity has increased and so, humidity levels are also expected to increase. But we have no study yet that we can refer to for increase of humidity over different regions,” said M Mohapatra, director general, IMD.
There is a 66% likelihood that the annual average global temperature between 2023 and 2027 will be more than 1.5 degree C above pre-industrial levels for at least one year. There is a 98% likelihood that at least one of the next five years, and the five-year period as a whole, will be the warmest on record, WMO cautioned on Wednesday.
“This report does not mean that we will permanently exceed the 1.5 degree C level specified in the Paris Agreement which refers to long-term warming over many years. However, WMO is sounding the alarm that we will breach the 1.5 degree C level on a temporary basis with increasing frequency,” said WMO Secretary-General Petteri Taalas in a statement.
“A warming El Niño is expected to develop in the coming months and this will combine with human-induced climate change to push global temperatures into uncharted territory. This will have far-reaching repercussions for health, food security, water management and the environment. We need to be prepared,” said Taalas.
There is only a 32% chance that the five-year mean will exceed the 1.5 degree C threshold, according to the Global Annual to Decadal Climate Update produced by the United Kingdom’s Met Office, the WMO lead centre for such predictions. The chance of temporarily exceeding 1.5 degree C has risen steadily since 2015, when it was close to zero. For the years between 2017 and 2021, there was a 10% chance of exceedance.
Who feels the heat?
Scientists who are part of WWA flagged that social vulnerability particularly religion, caste, gender, migration, and living conditions are critical when it comes to impact of extreme heat on people. “People are still recovering from disasters of covid, of extreme heat episodes of last year, of cyclones and extremely hard to recover or adapt because of the increased frequency of disasters. Age, gender, caste, hierarchy all determine how people are able to access certain resources. For example, the large number of informal settlements in areas affected by the April heat wave has an impact on whether accessed resources such as healthcare, cooling etc. Similarly, occupation also plays a central role such as street vendors and agricultural labourers who are out in the heat,” said Emmanuel Raju from Department of Public Health, Global Health Section & Copenhagen Centre for Disaster and co-author of the analysis.
Factors such as air pollution, the urban heat island effect, and wildfires further compound health impacts, particularly among the most vulnerable populations, scientists said.
There are a range of solutions to heat-related harms from the individual to the regional level. India among Bangladesh, Laos and Thailand has the most advanced heatwave planning presently. Solutions, such as self-protective action, early warning systems for heat, passive and active cooling, urban planning, and heat action plans can be effective at reducing fatalities and other negative impacts, the analysis said adding that people vulnerable in situations of extreme heat typically include the elderly, those with pre-existing medical conditions such as cardiovascular disease or diabetes, pregnant and breastfeeding women, those taking certain medications, and those with mental health considerations.