Temperatures are rising rapidly in many parts of the world especially in some of the major cities in India and even if we meet our Paris climate goals, nine major cities in the country including Delhi, Mumbai and Kolkata will continue facing heat stress for the foreseeable future.

This is according to a new study published in the US journal Proceedings of the National Academy of Sciences that looked at temperatures in 44 major cities across the world including nine in India to come to a conclusion that these cities will witness intensifying heat stress even if 2015 Paris climate targets are reached and could experience extremely hot days every year in the future. The nine Indian cities identified in the study are Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, and Surat.

Heat stress broadly refers to the human body experiencing more heat than it can tolerate, and is calculated using the heat index that incorporates both air temperature and humidity conditions.

If we rewind a little to the Paris agreement it was agreed by almost all countries in the world that they will limit the usage of fossil fuels so as to limit the rise in average world temperatures to “well below” 2.0 degrees Celsius (3.6 Fahrenheit) above preindustrial times.

While the goals are impressive and even if we manage to achieve it, not all cities in the world will be able to reap the benefits of the effort says the new study. According to the study even 1.5 degrees Celsius of warming above the pre-industrial time will amplify the current heat stress to the point that it is 5-6 times worse than in the recent past (1979-2005).

As a result of the amplification of the heat stress, as many as 350 million people will be affected in these 44 megacities for years to come. The study noted that cities in India: Delhi, Kolkata, Chennai and Ahmedabad, are already at the receiving end of this heat stress amplification and the West Bengal capital is the most heat-stressed among the 44 megacities across the world.

India faced a searing heat wave in 2015 that led to over 2000 deaths, and 2016 emerged as the hottest year since 1901. West Rajasthan, Gujarat and parts of Madhya Pradesh are already facing heat wave conditions.

According to authors behind the study, heat stress burden is greater in places with more people because the impact of the heat is larger. Authors add that the challenges that people face due to heat stress will increase in future because of rising air temperatures caused due to global warming and population increase.

If global average temperatures rise by 1.5 degrees Celsius, Mumbai will be added to the list of heat-stressed cities, authors note.

With a 2.7 degrees Celsius warming, that might be the result of the currently pledged targets for emissions reductions, both Hyderabad and Pune will become heat stressed. With 4 degrees warming Bengaluru will also enter the heat stressed zone.

Heat wave conditions usually form in India between March and June. Experts have listed increasing greenhouse gas emissions and the warming of the sea surfaces over the equatorial Indian and Pacific Oceans as possible factors.