Auckland's inner-city streets bake amid temperatures over 30C.

Construction workers toil in energy-sapping, near-unbearable, 90 per cent humidity.

Temperature records tumble.

This isn't the future, but the past: it's January 2019, when a warm blob of air slid off Australia and sent crowds toward beaches and ice cream parlours.

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Amid the relentless media coverage (one reporter went as far as trying to boil an egg on a Napier manhole) came news stories about climate-change projections.

It was a wake-up call that a warming world wasn't just an environmental emergency, but a medical one.

Focus: Three Kiwis share their perspectives on climate change. Video / Michael Craig / Alan Gibson

The Ministry of Health urged DHBs, councils and businesses to develop heat health plans as other countries had.

And for good reason: as soon as 2040, if the planet continued to warm on its present trajectory, Aucklanders might be sweltering through 10 to 15 days above 25C each year.

By 2110, there could be 70 to 80 of them.

Source / Niwa
Source / Niwa

When temperatures climb even above 18C, hospitals see a rise in patients with mental health and psychiatric conditions.

Stifling days are also linked to stress, aggression, heart attack and strokes.

Our most vulnerable - the elderly, the very young, migrants, ethnic minorities, the socially isolated and renters - would be hardest hit.

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Climate change threatened infectious diseases - including ones still foreign to us like dengue fever - but also warmer water, and heavier yet more infrequent rainfall events, that could set up more Havelock North-scale outbreaks of waterborne illness.

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With between 18,000 and 34,000 cases of gastroenteritis per year, the country already has relatively high rates compared with other high-income countries.

But by 2050, the World Health Organization has suggested New Zealand could expect about one to three more deaths of children because of all causes of diarrhoeal disease as a result of climate change.

Allergy sufferers could be sneezing their way through longer, more bothersome pollen seasons.

Exposure to two of the worst man-made air pollutants - PM2.5 and PM10 - could rise in step with heightened fire severity.

By 2110, there could be 70 to 80 days each year of temperatures over 25C. Photo / NZME
By 2110, there could be 70 to 80 days each year of temperatures over 25C. Photo / NZME

It's hardly surprising a growing number of doctors are pushing for climate-change action so these scenarios don't play out.

But, in tackling emissions, they also say we've been presented potentially the greatest global health opportunity of the century.

Better energy-efficiency measures like home insulation could mean less illness linked to cold, damp housing – leading causes of hospital admissions, particularly for Māori and Pacifika children.

Eating more plant-based foods and less red meat and animal fat could slash rates of heart disease and bowel cancer. Walking or cycling was not only good for physical activity, but also for reducing air pollution and road traffic injuries.

Tauranga GP Coral Dixon said her own family was taking its own steps to live more sustainably, through driving an electric vehicle, holidaying locally, using solar panels, eating vegetarian meals and cutting back on plastic.

This year, she joined her two daughters, aged 9 and 11, in school climate marches.

"In my opinion, we need to be acting as quickly as possible - and it would be gratifying to see New Zealand acting as a world leader in this area," Tauranga GP Coral Dixon says. Photo / NZME

"I've taken more of an interest in these issues over the last 10 years, and it becomes very clear to me that our own health and survival as humans is closely linked to the health of the planet and its complex ecosystems," she said.

"In my opinion, we need to be acting as quickly as possible - and it would be gratifying to see New Zealand acting as a world leader in this area.

"Individual everyday choices and actions will make a huge impact, as they demonstrate public opinion and sway political agendas," she said.

"I know there are many others doing some of these things and much more."

This story is part of the Herald's contribution to Covering Climate Now, an international campaign by more than 170 media organisations to draw attention to the issue of climate change ahead of a United Nations summit on September 23. To read more of our coverage go to nzherald.co.nz/climate