The world is warming and most people notice it on extremely hot days or when they have to pay the electricity bill in summer. However scientists have stated that the best way to measure Earth warming is not in the air, but the ocean.
A new study led by climate scientist Kevin Trenberth reveals that extra heat absorbing our planet is not distributed in a uniform way, but it’s mainly in two large belts of hot water, one in the Northern Hemisphere and one in the Southern Hemisphere, both near 40 degrees latitude. So, let’s learn more about this study, shall we?
Two ocean belts heating so fast
According to the study, more than 90% of the extra heat trapped by greenhouse gases ends up in the ocean and not in the atmosphere. This means that the ocean heat is one of the best indicators of global warming.
Trenberth and his team analyzed temperature data of the ocean up to 2,000 meters deep, by using data collected by thousands of Argo floats and other instruments between the years 2000 and 2023. When they averaged this data by latitude, they saw a clear pattern:
- In the tropics, warming is irregular because of natural events like El Niño and La Niña, which move heat back and forth across the Pacific.
- In the mid-latitudes (around 40° north and 40–45° south), the warming is steady and stronger than in other regions.
- In the subtropical zones (around 20°), long-term warming has been surprisingly low.
The Southern Hemisphere belt is particularly intense, stretching from south of New Zealand to Argentina and Tasmania, including the Southern Ocean. These waters have absorbed more heat than almost anywhere else on Earth.
How winds and currents concentrate heat
What most people would think is that these areas heat up simply because they receive more sunlight, but Trenberth’s study shows that heat is concentrated by ocean and atmospheric movements.
Scientists combined satellite radiation data with measurements of winds, humidity, and temperature and found that:
- Strong ocean currents, such as the Gulf Stream and Kuroshio Current, carry heat and concentrate it in the Northern Hemisphere belts.
- In the Southern Hemisphere, stronger westerly winds that have shifted toward the poles push warm water into the 40°S belt while cooler deep water rises elsewhere.
- These movements act like a “conveyor belt,” piling up heat in the belts instead of spreading it evenly.
Why this ocean warming matters
The warming of these ocean belts has direct effects on everyday life, especially for people living near the coasts:
- Marine heatwaves damage coral reefs, kelp forests, and fisheries.
- More evaporation leads to heavier rainfall and stronger storms.
- Sea levels rise faster in these regions because warm water expands.
Behind the hot belts
Something important that the study also emphasizes is that human-made greenhouse gases are the main reason for the long-term heat buildup. However, other factors amplify it, like:
- Natural variations such as El Niño, La Niña, and Pacific cycles.
- Cleaner air in parts of the Northern Hemisphere allows more solar energy to reach the ocean.
So…
The next time you hear about record heat or extreme storms, remember: much of that energy is coming from these hidden hot belts in the ocean. The oceans are the Earth’s thermometer—and right now, they’re telling us something urgent: it’s time to act.