The climate in tropical regions could become unrecognisable by the end of this century if the world does nothing to slow global warming, a New Zealand scientist says.
A Kiwi author of a major study published today in leading journal Nature Climate Change also says New Zealand will have a "normal" climate vastly different to what we experience today if global emissions go unmitigated.
The study emphasises the human dimension of how unusual a warmer climate would appear to people living in different regions - particularly the billions of people living in tropical and mid-latitude parts of the planet.
The research identifies a new climate as "unfamiliar" if a year that is now normal would only have occurred once in an individual's lifetime, or as "unknown" if it would have occurred once every few hundred years or more, on average.
"Overall, we found new climates emerge faster in inhabited areas, especially in the tropics, than in the world as a whole," said lead author Professor Dave Frame, of the Victoria University of Wellington.
"People living in tropical regions, such as the South East Asian nations and the Pacific Islands, are almost certain to experience 'unfamiliar' or even 'unknown' climates by the end of this century if climate change is not slowed down."
The situation was almost as stark for many tropical African countries as well, Frame said.
"Young people alive today who are currently in the labour force in Colombia or Indonesia - if we keep on a high-fossil fuel trajectory, then, by the time they retire, they won't recognise the climates compared with those from when they are young ... they'll be totally different.
"Even New Zealand will have a pretty unrecognisable climate by the end of the century if we don't mitigate fairly strongly - but it's our Pacific friends who really have a lot on the line here.
"Everyone talks about sea level rise and what happens in 500 to 1000 years' time, but actually, there's a lot of change happening now that's front-loaded and they are on the sharp end of it."
The emerging effects of climate change in the coming decades could however be dramatically reduced with mitigation efforts.
"Unknown climates might be expected before 2050 in many tropical areas, and before the end of the century in mid-latitude areas," said co-author Dr Manoj Joshi of the University of East Anglia.
"However, many people alive today could reap the benefits of slowing or stopping climate change."
Projections of 21st century climate made with significantly reduced carbon emissions show that tropical climates, especially those areas with very high populations, could avoid such emergence, staying far more "familiar" to the people who live there.
Frame said cutting emissions now would do a huge amount to keep climates more familiar than they would otherwise become.
"Many of the beneficiaries of climate change mitigation include today's young adults, people already working, paying taxes and, where institutions permit, voting.
"As this becomes understood, it has the potential to be a powerful motivating factor."
Meanwhile, another study in the journal suggested leafy canopies may be slowing the Earth's warming.
A team of international researchers looked at satellite images, crunched some numbers and found that leaves may have slowed down warming by around one tenth of a degree since the early 1980s.
This was mainly because of more water rising up from the soil and leaves, and changes to how air circulated, the authors said.
Expert: World 'better off' without US in Paris Agreement
A climate policy expert has argued the world would be better off if the US withdraws from the global climate agreement finalised in Paris last year.
The White House has said it is close to a decision on whether the US will remain in the Paris Agreement on climate change.
In a commentary published in Nature Climate Change, Australian National University researcher Dr Luke Kemp said a "rogue" US could cause more damage inside rather than outside of the global agreement.
"Having the US remain under the Paris Agreement would reveal the weaknesses of the agreement, prevent new opportunities from emerging, and gift greater leverage to a recalcitrant administration," he said.
Kemp said continued US membership in the global agreement on climate change would be symbolic and have no effect on US emissions.
"The Paris Agreement is procedural: it requires a new pledge every five years, but doesn't limit the actions of the US," he said.
"The US will likely miss its target and cut climate financing regardless of Paris."
There was little evidence to suggest that the US dropping out will trigger a domino effect, Kemp said.
"Countries are more likely to withdraw or renege on their actions because the US misses its target, eliminates its financing and reveals how weak the Paris Agreement really is," he said.
"If the US remains under the agreement it will keep a veto in the negotiations.
"The US could use its voice and veto to water down the rules and details of the Paris Agreement, which are currently being negotiated. Giving the former head of ExxonMobil a seat at the table is a terrible idea."
Kemp concluded that the pushing for the US to remain was short-sighted.
"The international community should be more concerned about the actions of the US, rather than whether they are symbolically co-operating," he said.
"A withdrawal could trigger new opportunities to emerge, such as carbon border adjustments and forceful leadership from the EU and China."
New Zealand, which reported a 23 per cent increase in greenhouse gas emissions between 1990 and 2014, has pledged under the agreement to slash its greenhouse gas emissions by 30 per cent from 2005 levels and 11 per cent from 1990 levels by 2030.