Heatwaves turned sea into warm bath
Scientists have shed fresh light on two of the most freakish climate events in New Zealand’s history — and warned they’re likely to become more common as our planet warms.
A new study led by climate scientist Professor Jim Salinger has investigated back-to-back “marine heatwaves” that turned the country’s coastal seas into warm baths and drove mass-melting of our glaciers over the summers of 2017-18 and 2018-19.
Salinger said the twin events were the result of an “atmospheric and oceanic stew” including blocking anticyclones centred over the Tasman Sea, fewer low pressure systems, and a strongly positive Southern Annular Mode.
When this effect was positive, the massive storms that rage in the “roaring forties” and “furious fifties” latitudes in the southern oceans contract toward Antarctica, instead of in our direction.
The combination of that and a strong La Nina climate system in the tropical Pacific — known to drive more anticyclones east of New Zealand — brought many more anticyclones to our region, while blocking cold swells surging up from the deep south. But he and his colleagues also pointed to the hand of human-driven climate change, noting that the Tasman had been warmer over the years leading up to the events.
The effects of the heatwaves were dramatic: air temperatures over the country reached between 1.7C and 2.1C above average, while sea surfaces heated up to between 1.2C and 1.9C above average.
Even more dramatic observations included snapper being caught in Doubtful Sound for the first time ever.