A new study has shown that temperatures in parts of South Asia could reach unsurvivable levels before the turn of the next century.
The research ties to rising wet-bulb temperature, a way of measuring the air's humidity. Across swathes of India, Pakistan and Bangladesh, coming heat waves could see the wet-bulb temperature reach 35C, considered the upper limit of temperatures humans can survive in.
As the humid air reaches that level, it leaves the human body unable to properly regulate its internal temperature - one that needs to stay within a small margin.
The areas likely to be hit is also a cause for concern - some of the poorest in the region where many live on subsistance farming and hard labour while having little access to services like air conditioning.
The researchers from the Massachusetts Institute of Technology and Loyola Marmount University said that the findings raise new issues of environmental justice around climate change policy discussions.
"In the absence of serious mitigation, some of the most severe hazards associated with climate change will fall on some of the most vulnerable populations," the paper by Eun-Soom Im, Jeremy S. Pal and Elfatih A. B. Eltahir said.
The study also noted the India itself has had rapidly increasing levels of greenhouse gas emissions as its economy and population has boomed. "The findings from this study may present a significant dilemma for India because the continuation of this current trajectory of rising emissions will likely impose significant added human health risks to some of its most vulnerable populations," the study said.
Speaking to the BBC, Professor Eltahir said "climate change doesn't look like an abstract concept if you look at India." Before adding: "This is something that is going to impact your most vulnerable population in ways that are potentially pretty lethal. But it is avoidable, it is preventable."