Warming is affecting oceanic currents including ENSO (El Niño and La Niña) and the Antarctic Circumpolar Current. These play a significant role in the world’s climate, with heatwaves supercharging New Zealand storms and affecting oceanic ecosystems.
Warmer water carries less oxygen than cold water, so marine heatwaves are changing oceanic ecosystems in multiple ways from ocean acidification and heat stress leading to coral bleaching and mass death of marine life (top image), affecting oceanic ecosystems
See the National Science Challenges research (Video 2) on the link between marine heat waves and climate extremes. To monitor
the occurrence of such extreme events around New Zealand, a marine heatwave forecast tool has been developed as part of the Moana Project.
Deeper ocean heatwaves are not felt at the surface, so about half are not being recorded:
Annual number of subsurface marine heatwave shows a significant increase in response to subsurface mean-state warming during the past three decades. Our findings reveal the limitation of identifying marine heatwaves solely based on the sea surface temperature and underscore the necessity of subsurface observations for monitoring marine heatwaves. – Sun et al, October 2023
Warming of the oceans and associated deoxygenation are altering marine ecosystems. Current knowledge suggests these changes may be reversible on a centennial timescale at the ocean surface but irreversible at deeper depths even if global warming were to ameliorate. – Santana-Falcón et al, 2023
We have breached 7 out of 9 Planetary Boundaries. In this 2025 edition, we assess for the first time that Ocean Acidification is the seventh transgressed Planetary Boundary – Planetary Health Check Sept. 2025
During austral [southern hemisphere] summer 2017/18, the New Zealand region experienced an unprecedented coupled ocean-atmosphere heatwave, covering an area of 4 million km2. Regional average air temperature anomalies over land were +2.2°C, and sea surface temperature anomalies reached +3.7°C in the eastern Tasman Sea… The event persisted for the entire austral summer resulting in a 3.8 ± 0.6 km3 loss of glacier ice in the Southern Alps (the largest annual loss in records back to 1962)… The best match suggests this extreme summer may be typical of average New Zealand summer climate for 2081–2100, under the RCP4.5 or RCP6.0 scenario. – Salinger et al 2019
Rather than a glimpse into what summers might be like after 2081, the warming over the ocean increased the following year (Fig. 5). Then in the summer of 2019/2020 something extraordinary happened:
In an event that is unprecedented in 40 years of record-keeping, temperatures over Antarctica rose rapidly, causing the polar vortex over the Southern Hemisphere to break down and even reverse direction. This had cascading effects on weather patterns. – Freedman, January, 2020
Marine heatwaves occurred every year since then. Once global average temperatures exceed 1.5°C (this occurred 2023-2024) extreme marine heatwaves that occurred on average once per century, are more likely to occur ever decade. At +3.5°C, the worst case scenario and our current climate trajectory:
…the number of marine heatwave days is projected to increase by a factor of at least 40. At this level of warming, marine heatwaves have a spatial extent that is over 20 times bigger than preindustrial levels… Under high future emissions, by the late 21st century, much of the global ocean may reach a permanent state of marine heatwave, relative to a fixed pre-industrial threshold. – Marine Heatwaves International Working Group (PDF, 2021).
Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it much faster than the snow and ice.
