Storm clouds rolling into Wellington on 12 August, 2024. Photo: Supplied / James Bass
A climate scientist has discovered that two specific bands of the globe are warming faster than elsewhere.
Auckland University's Dr Kevin Trenberth led a study examining where heat - captured by the ocean - travels and accumulates.
The first band - at 40 to 45 degrees latitude south - is heating at the world's fastest pace, with the effect especially pronounced around New Zealand, Tasmania, and Atlantic waters east of Argentina.
The second band is around 40 degrees north, with the biggest effects in waters east of the United States in the North Atlantic and east of Japan in the North Pacific.
Dr Trenberth said it could be why storms that track to New Zealand - from an area warming at a slower rate - seem to strengthen once they get there.
He said it's "striking" and "unusual" to see such a distinctive pattern.
"It turns out there are changes in ocean currents going on, coupled with changes in the atmospheric circulation - changes in the jet stream - and where all of the storm tracks are going."
The heat bands have developed since 2005 in tandem with poleward shifts in the jet stream (powerful winds above the Earth's surface that blow from west to east) and corresponding shifts in ocean currents, according to Trenberth and his co-authors in the Journal of Climate.
Trenberth said most Pacific Island nations fall within the subtropics, which are "still quite warm" but heating at a slower rate.
But they are effectively sandwiched between the two bands where harsher storms form more frequently.
In areas which are warmer, Dr Trenberth said that stronger storms with heavier rainfall are fuelled as they pick up more moisture, taking heat out of the ocean, and sending off along their track.
"No doubt the heat will come back into these regions, because of the way in which the winds are changing in the atmosphere."
For New Zealand and its neighbours, Dr Trenberth said that these findings could help explain why each new year breaks heat records.
"It comes back to what is really going on in the oceans," he said.
"They have now warmed up so that they are major players in the global warming picture."
