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How bad it will get all depends on what happens over the next few decades, or even the next one.
The best-case scenario is that the world succeeds in ramping down man-made emissions of carbon dioxide, within this century, to net zero.
Mean global warming would likely flatten off a little under 2degC above pre-industrial temperatures - the target number of the Paris Agreement that New Zealand and about 200 other nations are signed up to.
But even under this optimistic trajectory, our world would still be transformed and face a big change in extreme events like floods and droughts.
The world's rainfall levels could rise or drop by 10%, and the number of heatwaves and the risk of forest fires would soar.
The worst-case scenario
A high-carbon future - as the world is on track to experience if it continued to pump out carbon dioxide at its current rate - would be much bleaker.
"By just another human lifetime away, people could be living in a climate outside anything that any of us have ever experienced,'' Victoria University climate scientist Prof James Renwick said.
"The potential for mayhem is astronomical and it really could be catastrophic.''
The Arctic could lose all of its summer time sea ice and oceans could be 1.5m higher, with another 10m locked in over coming centuries.
In New Zealand, only another metre of sea level rise would add 116,000 people to the 72,000 - and $12.5billion worth of buildings - already exposed to extreme coastal flooding.
Temperatures might be 3degC or 4degC higher than today, and warm summer days in Canterbury and Hawke's Bay could reach the high 40s, he said.
Most of New Zealand could be in a subtropical climate, at least, with heavy rainfall events possibly double the current amounts.
Drier, eastern parts of the country would have long, very severe droughts, and forest fire risks would rise by a factor of five.
By the end of the century, many parts of the country would record more than 80 days a year above 25degC.
Most places typically experienced those temperatures for only between 20 and 40 days now, but, already, about 14 elderly people in Auckland and Christchurch have died when temperatures exceeded 20degC.
With about one in four New Zealanders projected to be 65 and over by 2043, the problem would be amplified.
In the Pacific, where about half the population live within 1.5km of the ocean, even a further 2degC of warming could result in small island countries being inundated by sea-level rise.
What needs to happen now
If warming continues at the current rate, the Paris Agreement's aspirational threshold of 1.5degC - and that of New Zealand's Zero Carbon Bill - will be crossed at some point between 2030 and 2052.
If the 1.5degC threshold can be held, the world could escape an extra 10cm of sea level rise, above what's already been locked in for this century.
If the world cannot hold the line, then the 2degC threshold - the ultimate limit the Paris Agreement was built around - could be over-shot only about a decade later.
"I can guarantee that climate models do not lie.
"If we don't take action, it's going to be a very difficult future,'' Prof Renwick said.
• This story originally appeared in The New Zealand Herald. It is republished here, in edited form, as part of the Otago Daily Times' partnership with Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.
- By Jamie Morton