New Zealand's wastewater-contaminated beaches a sign of what global warming could bring

As the sun comes back out across the country, "unsuitable for swimming" signs are also going out at many popular beaches.

The wild weather and heavy bouts of rain have forced wastewater treatment plants to overflow - contaminating waterways and popular swimming spots.

And it is a sign of what's to come with global warming.

On a typical summer's day at Wellington's Oriental Bay, and just around the corner at Lyall Bay, surfers and swimmers were seen ignoring warning signs that faecal matter could be present.

"If there was more signage out then I don't think anyone would be in the water," said one Wellingtonian.

Heavy rain this week forced 38,000 litres of waste to overflow into the ocean just south of Lyall Bay, and it's a similar story at many beaches across the motu.

A map from Land Air Water Aotearoa (LAWA) shows red spots at beaches and rivers that are unsuitable for swimming due to contamination and wastewater overflow, while orange advises caution.

Climate scientist James Renwick told Newshub that Aotearoa's infrastructure is not prepared for global warming.

"Our water infrastructure in a lot of places is 100 years [old] and is built for the climate we used to have, not the climate we have now."

The latest data released by NASA on Friday showed global temperatures rose, on average, 1.1C above pre-industrial norms in 2022.

That's dangerously close to the limit of 1.5C that scientists say can not be exceeded if we're to avoid catastrophic warming by the end of the decade.

Overall, last year was the 5th hottest year ever recorded.

"These latest years, they're the warmest on record, but they are going to be some of the coldest of the next fifty years," Renwick said.

And the warmer temperatures will fuel more extreme fires, flooding and hurricane-like events.

"As you warm the air you end up with more water vapour, more moisture in the air and more evaporation from the ocean surface, so there's more fuel for rainfall events," Renwick told Newshub.

The new Three Waters reforms are planning for the future so that wastewater and stormwater systems can cope.

"This is a problem for the world. For every system in every country, they are having to deal with how do they balance with increasing the size of systems to deal with this increased rainfall, at the same time at ensuring it is affordable," said the head of technical Three Waters reform Lorraine Kendrick.

But the upgrade to our drainage systems can't come soon enough, with significant weather events and the contamination of our beaches likely to become harder to deal with.