Many of the world's poorest countries are already experiencing hotter days as a result of climate change while more affluent countries are much less affected.
Heat extremes are quickly becoming more frequent for countries near the Equator, which are generally poorer, according to research published by Victoria University today.
New Zealand Climate Change Research Institute professor David Frame said most of the world's less advantaged countries are in tropical climates.
"Low-latitude regions have less variability in day-to-day temperatures when compared with mid-latitude climates," Professor Frame said.
"Which means the 'signal' of climate change emerges quite quickly, and because of this, the frequency of extremely hot days increases rapidly too."
It means many of the poorest people in the world are experiencing much greater increases in very hot days when compared with people living in wealthier countries.
Now the process has started, it is likely that it'll continue into the future.