The world's poorest people are suffering more extreme heat driven by climate change while wealthier nations, including New Zealand, remain less affected.

That's the big picture of a new international study, co-authored by two Kiwi researchers, which draws one of the first links between times of emergence of extremely hot days with cumulative emissions of carbon dioxide (CO2).

It showed that heat extremes were quickly becoming more frequent for mainly poorer nations nearer the equator.

The study, published today in scientific journal Environmental Research Letters, used climate models to simulate cumulative CO2 emissions and changes to extreme daily temperatures over the 20th and 21st century.


An extremely hot day was defined, relative to local climate, as occurring 0.1 per cent of the time in the pre-industrial climate.

Co-author Professor David Frame, of the Victoria University-based New Zealand Climate Change Research Institute, said low-latitude regions had less variability in day-to-day temperatures when compared with mid-latitude climates.

This meant the "signal" of climate change emerges quite quickly and, because of this, the frequency of extremely hot days increased rapidly too.

"This means because of where they live, many of the poorest people of the world are experiencing much greater increases in the number of very hot days when compared with the wealthiest countries of the world."

It was partly true that countries least affected by the extremes were also the biggest CO2 emitters: China, the US and Russia alone contributed around half the total.

New Zealand's contribution of total emissions is about 0.15 per cent.

• The image shows how some regions (in red) will experience two-fold, 10-fold and 50-fold increases in hot days relative to cumulative emissions of CO2. Source: VUW, NIWA, ETH Zurich, Met Office Hadley Centre, University of Reading, University of East Anglia

Victoria University PhD student Luke Harrison, who also contributed to the paper, said rapid increases in hot-day frequency appeared likely to continue into the future.

"Even if heat extremes were becoming more frequent for all countries at the same rate with climate change, we know the wealthiest countries will be able to cope more easily than poorer nations."

Importantly, the disparity between the global rich and poor would only continue to get worse as countries emitted more CO2 into the atmosphere.

Professor Frame said that although New Zealand was a comparatively wealthy country and not exposed to the worst of the heat extremes, it did have very strong links to the Pacific countries, which were.

"Their climate patterns are normally very regular, so a small shift is a big relative deal."

The identified effects on these island nations were separate considerations from sea-level rise, something also driven by climate change.

Professor Frame was now exploring contributions to climate mitigation efforts by nations relative to their emissions.

The concept of "loss and damage", where rich, big-polluting countries provide aid or compensation to poorer nations for damages, such as infrastructure lost to rising seas -- has been a long-standing talking point yet to be fully resolved by UN-led negotiations.