New research reveals two rapidly warming oceanic bands near 40° latitude, with New Zealand situated in the most affected southern zone, posing significant risks to marine ecosystems and global climate patterns.
Key Points at a Glance
- Two oceanic bands near 40° latitude are experiencing unprecedented warming.
- New Zealand lies within the fastest-warming southern band.
- Warming linked to shifts in jet streams and ocean currents since 2005.
- Impacts include disrupted marine ecosystems and intensified extreme weather events.
A new study led by renowned climate scientist Dr. Kevin Trenberth, affiliated with the University of Auckland and the National Center for Atmospheric Research (NCAR), has uncovered two zones of rapidly warming ocean water that circle the globe near the 40° latitude lines in both the Northern and Southern Hemispheres. These two bands, each hundreds of kilometers wide, are absorbing more heat than any other region of the ocean—and the consequences could be profound.
The southern band, which includes waters around New Zealand, Tasmania, and parts of the South Atlantic, has emerged as the fastest-warming oceanic region on the planet. Meanwhile, its northern twin, located east of the United States and Japan, is experiencing similarly concerning increases in ocean heat content. These patterns were revealed by a detailed analysis of ocean temperature data from 2000 to 2023, comparing recent observations with a 2000–2004 baseline.
What makes these findings especially important is the scale and consistency of the warming. The research tracked changes in ocean heat content down to 2,000 meters, offering a three-dimensional picture of how heat is distributed throughout the water column. This approach paints a more accurate and alarming image of oceanic warming than surface temperatures alone.
These bands are warming so rapidly in part because of shifting jet streams and ocean currents—phenomena influenced by the same greenhouse gas accumulation that drives global climate change. The jet streams in both hemispheres appear to be moving poleward, nudging oceanic currents into new patterns that facilitate more intense heat uptake in specific regions. This shift has been particularly evident since around 2005, a turning point when these warming trends began to accelerate markedly.
Beyond temperature metrics, the study highlights the cascading effects on marine systems. Warmer oceans hold more moisture and energy, which can supercharge storms and drive unpredictable weather patterns. Marine ecosystems—especially those reliant on cooler water temperatures—face existential threats, with fish stocks migrating, coral reefs bleaching, and plankton populations destabilizing. Such changes can ripple outward into global food chains, economic systems, and weather events far from the ocean itself.
Interestingly, while these 40° bands are warming rapidly, the study also identified regions near 20° latitude, especially in the subtropics, where ocean temperatures have remained surprisingly stable or increased far less than expected. This uneven distribution of ocean heat complicates climate modeling and raises new questions about where and how the planet absorbs excess energy from greenhouse gas emissions.
Trenberth stresses that natural climate variability contributes to these changes but is far from the sole cause. Instead, the driving factor is anthropogenic—human-caused—greenhouse gas emissions. The ocean, which acts as Earth’s largest heat sink, absorbs over 90% of the excess energy trapped by greenhouse gases. Understanding where this heat goes is essential to forecasting and preparing for future climate impacts.
New Zealand’s geographic position within this southern hot zone places it on the frontline of these changes. The surrounding waters are critical to the nation’s climate, biodiversity, and economy. From fisheries to agriculture and coastal infrastructure, the implications of warmer oceans are vast and deeply interwoven into the fabric of society.
As Dr. Trenberth and his colleagues point out, this is a call to action. Monitoring and modeling ocean heat must become central components of climate strategy—not only to understand global warming but also to mitigate its worst impacts. With marine heatwaves becoming more frequent and severe, better ocean observations are vital for preparing communities, adapting ecosystems, and guiding international policy.
The study’s findings shine a spotlight on just how dynamic and uneven climate change can be. Rather than uniform warming, the planet is experiencing an increasingly complex pattern of regional effects, influenced by geography, oceanography, and atmospheric physics. This complexity makes scientific understanding and public awareness more important than ever.
Source: University of Auckland
