Nearly 46°C in Delhi, and temperatures approaching 48 degrees in Pakistan. A record heat wave has hit these two countries, causing power cuts and water shortages for millions of people who are expected to suffer from this furnace. This extreme heat wave is expected to rage for another five days in northwestern and central India, until the end of next week in the east of the country as well as in Pakistan.
These exceptional temperatures are accentuated by climate change. They bear witness to global warming causing increasingly intense extreme weather phenomena, explains the meteorologist and forecaster at Météo France, Gaétan Heymes.
L’Express: A strong heat wave hits India and Pakistan. What is exceptional about it?
Gaetan Heymes: For several days now, there has been a major heat wave which is setting up and intensifying throughout Pakistan and a large part of India. These regions are used to very hot weather at this time of year, between April and June, but what is different this year is that the heat wave started early. By the end of March, parts of Pakistan had already seen temperatures above 45 degrees Celsius. For several days, these heats have intensified with up to 47 degrees in Pakistan on Wednesday and 46 in India.
These temperatures are also exceptional for the season, the average is rather around 40 to 42 degrees at this time of the year and this heat will increase further in the coming days. The peak in temperatures should peak a priori at the beginning of next week and depending on the location, the values could approach or even reach 50 degrees under shelter, which would bring us closer to the temperature records in these countries: in Pakistan, the record for one month in April is 50.3 degrees in 2018, and in India the last record dates from 1958 with a peak of 48.5 degrees in Rajasthan.
The duration and extent of this wave raise fears of serious health consequences…
A very punctual episode of heat will not have major consequences in terms of health, but what makes the severity of a heat wave is its duration, combined with its intensity. This is what we are currently observing in the region, with very high temperatures for several weeks and which continue to rise. This raises fears of serious consequences for frail people, especially in those populations where poverty levels and population density are particularly high.
How can we explain this heat wave?
Several very strong heats have been observed in the world lately. There are strong anticyclonic anomalies which are set up at altitude, with a blockage of warm air in the lower layers of the atmosphere. The phenomenon observed in India and Pakistan is relatively similar to that of heat waves in Europe. But for there to be these very strong heats, the air must be dry and this is generally the case for a few weeks before the monsoon in this region. There is a conjuncture between the calorific potential of the air mass which increases when we approach summer, as everywhere in the northern hemisphere, coupled this time with the absence of humidity, which makes temperatures less easily bearable.
This anticyclonic anomaly is currently observed over a large part of Asia. From India and Pakistan to Kazakhstan, even to southern Siberia. This entire geographic area is experiencing very high temperatures for the season.
In March, the Antarctic continent also experienced unprecedented temperatures, heat records are regularly observed… These heat waves, always described as exceptional, are they not becoming a new norm?
What was observed in Antarctica in March was indeed exceptional, but it is a meteorological phenomenon that is totally independent of what is happening today in India and Pakistan. On the other hand, in a context of an increasingly hot climate, when these situations occur, they lead to increasingly intense phenomena. For the same situation on paper; we observe higher temperatures today than twenty or thirty years ago, because the atmosphere has warmed up in the meantime.
Global warming has already been in place since the beginning of the pre-industrial era (we have warmed the atmosphere by almost 1.1°C), so extreme events are already more intense than those of yesterday. And that is why we are increasingly breaking heat records and conversely cold records. But the more we warm up the atmosphere, the more what is exceptional today, like this episode of heat, will become less exceptional in a few years, even recurrent.
Are we able to anticipate these waves?
It is difficult to anticipate the amplitude of these meteorological phenomena but we can give a frequency and a probability of occurrence. For example, determining what the probability of an exceptional event occurring will be, and this obviously depends on the future of the climate and the various scenarios of greenhouse gas emissions. What has a 1 in 200 chance of happening today may only have a 50 chance in 50 years, or even a 1 in 10 chance. But it is not because we observe a warming of 1°C on a global scale that extreme events will be amplified by 1°C, there are many meteorological processes that are not linear.
How high will the temperatures rise during the most intense waves? It is an unknown factor in the response of the atmosphere to climate change, extreme phenomena are inherently difficult to predict and even to model in climate models. For example, last year’s awe-inspiring “heat dome” phenomenon observed in Canada surprised many forecasters because we didn’t think it was possible to reach temperatures above 50 degrees Celsius at such latitudes on the globe. There are attribution studies that are conducted during such intense weather events that show that these events are virtually impossible without the effects of global warming.