Covering climate now series: Forecasting in a warming world

How do you commentate on a catastrophe in slow motion?

Welcome to the world of Niwa's Ben Noll.

The New Yorker has become one of our most visible and energetic meteorologists, fielding reporters' calls on everything from hail to heatwaves, in between spending eight hours a day making sense of a constant stream of data and guidance.

Trying to explain the blurry influence of a warming planet on our day-to-day weather isn't easy - if just for the simple reason that climate isn't the same as weather.

"No single event is caused by climate change, but each has what you might call a climate change handprint," the Niwa forecaster says.

"It might be that more moisture has come with warmer seas, or that a heatwave has been made more likely, because we live in an Earth warmer than it was even four or five decades ago."

Back in July 2014, a storm slammed into Northland, putting thousands of hectares of dairy land underwater and causing some $18m in damage.

Amid that five-day deluge, a young mother drowned at Haruru Falls and emergency crews had to mount more than a dozen rescues.

It was one of the worst weather events in the region's history. It was also one of only a handful ever studied here for their direct link to climate change - global warming effectively doubled the chances of the event happening.

Already, climate change has lifted our land and sea temperatures; contributed to 22cm of sea level rise in the past century; driven acidification of our oceans; and helped strip our glaciers of a third of their ice within just four decades.

In some parts of the country, climate change has been manifesting with drier soils, fewer frost days and shifted rain patterns.

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It's been implicated, among other drivers, in our hottest summer (2018) and our hottest year (2016).

Noll said that, while we couldn't precisely say to what extent climate change was a driver in a given weather event, it was an area of emerging research.

Today, a team of New Zealand researchers are working under a new million-dollar project aimed at picking the picture apart.

The model they're working toward, building off a decade of data, would tell us the exact difference that climate change made to an event like the Northland storm – and within just a day or two of it happening.

Not too long ago, people in Noll's line of work were reluctant to even touch the subject.

What comments forecasters did make were limited to pointing out that a big rain event, or a drought, was what we could expect under a projected warmer future.

"Even just going back a decade, we meteorologists were just sticking to the weather.

"Over time, a lot more literature has come out about increasing global temperatures and precipitation extremes. That's probably opened a lot of our eyes to it – even those who were 50/50 about its influence."

But it was still a fine line to tread.

Noll pointed to the long-term average Niwa used to categorise temperatures as below, near or above average.

Under the current baseline - comparing our average temperatures today to what New Zealand experienced between 1981 and 2010 – the country has seen more than 30 consecutive "above average" months, largely as a result of warmer coastal seas.

That baseline was about to shift to the 1991 to 2020 period, meaning we soon might hear more months being described as "average" again.

"Yet, if you want to compare a month today with the 1971 to 2000 stretch, it's going to be apples and oranges."

Another tricky issue was how to discuss balmy weather in the middle of winter.

"There was a day this winter that was actually really warm, for winter standards – it was about 17C or 18C, and obviously well above average for that time of year," he said.

"We posted about it in a positive light, like, you know, hey, enjoy the warm weather, but in some of the feedback we got, people told us, should we really be enjoying this? Is this a sign of climate change? So I'm really fascinated about how we go about communicating this stuff."

The most common question he fielded from friends was still whether climate change was actually happening, but he suspected that question would soon shift to "how will climate change affect me?"

When it comes to the climate and weather itself, scientists have given us plenty of broad projections.

For instance, Wellington's 2050 climate will resemble Auckland's today, while Auckland will feel more like Sydney.

Average temperatures would be, at best, 0.5C warmer than today - meaning roughly 50 per cent more heatwaves, more droughts and more river floods.

Other estimates have indicated that, by that time, and with 30cm of sea level rise, a one-in-100 year flood would become an annual event in Wellington, a one-in-two year event in Dunedin, and a one-in-four year event in Auckland.

The once-in-a-century January 2011 storm that put much of Auckland's Northwestern Motorway underwater would also happen once every four years - and 40cm would make it a two-year occurrence.

By the end of the century, assuming greenhouse gas emissions continued to climb close to current levels, many parts of our country will record more than 80 days a year above 25C.

Most places typically only have between 20 and 40 days above that now, yet, already, about 14 elderly people in Auckland and Christchurch die each year when the mercury climbs above 20C.

"There are some people who are really downtrodden about climate change," Noll said.

"For me, and maybe it's the way I'm wired, I try to see it through a bit more of a positive lens. I see it as a time of opportunity. We can still control our own destiny, but granted, even if we stopped sending carbon dioxide into the atmosphere now, it's going to take a long time to really turn that knob off."

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