New Zealand’s sea temperatures have reached record highs, surpassing global averages.

New Zealand’s sea temperatures have reached unprecedented highs, significantly exceeding global averages and raising concerns about the health of local marine life and ecosystems. Experts emphasize that this new data dispels the belief that New Zealand is shielded from extreme temperatures.

According to recent data from Stats NZ, oceanic sea-surface temperatures in New Zealand have risen between 0.16–0.26°C per decade since 1982, and coastal waters have warmed by 0.19–0.34°C per decade. Both oceanic and coastal regions recorded their hottest years in either 2022 or 2023.

Matt Pinkerton, a principal scientist at the National Institute for Water and Atmospheric Research, stated that the rate of ocean surface warming around New Zealand has doubled the global average of 0.18°C per decade over the past 20 years, with the Chatham Rise region experiencing temperatures three times higher than the global average. This trend is attributed to New Zealand’s geographic position, which exposes it to warming from the Pacific, Tasman Sea, and Southern Oceans.

“New Zealand’s high temperatures disprove the notion that the island nation is protected from extreme temperatures,” Pinkerton said. “Being surrounded by so much ocean, we thought we were somewhat shielded from the warming effects, but this data indicates otherwise.”

Marine heatwaves—extended periods of unusually warm seawater—have also intensified. The Western North Island experienced heatwave conditions for 89% of 2022, the highest among coastal regions, while the Tasman Sea spent 61% of the year in a heatwave, the highest among oceanic regions.

Stuart Jones, the environmental and agricultural statistics manager at Stats NZ, noted that even small temperature increases can disrupt marine ecosystems, cause species to relocate, and elevate disease risks. Past marine heatwaves have led to significant ecological impacts, including mass sea sponge bleaching, die-offs of southern bull kelp, large-scale fish strandings, and penguin deaths.

Dr. Christopher Cornwall, a marine biology lecturer at Victoria University of Wellington, warned that intense marine heatwaves could cause large-scale ecological changes by killing habitat-forming species such as kelp. “Both the background warming and more frequent, intense, and longer marine heatwaves are likely already permanently altering these marine ecosystems within Aotearoa.”

Cornwall and Pinkerton stress that the full impact of warmer oceans on ecosystems remains poorly understood, underscoring the need for long-term monitoring to anticipate and plan for changes, especially regarding fishing quotas.

A separate Stats NZ dataset revealed that phytoplankton, microscopic algae that form the base of marine food webs, are decreasing in New Zealand’s warmer northern waters, correlating with rising sea-surface temperatures.

Dr. Georgia Grant, a climate scientist at GNS Science, added that New Zealanders will also feel the effects of warming seas, as the ocean heavily influences the island nation’s weather. The world’s oceans have absorbed about 90% of the extra heat generated by human-caused climate change, contributing to the increased severity of storms like Cyclone Gabrielle under climate warming conditions.