A hot baseline, then another hot year
Global sea-surface temperatures (60°S–60°N) in July and August 2025 ranked among the warmest on record, only just behind highs in 2023–2024. Regions like the Mediterranean and parts of the North Atlantic saw notably strong marine heatwaves. That means large swaths of the ocean running months above their usual seasonal averages.
Why this is happening
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Human-driven warming: The ocean absorbs the majority of excess heat from greenhouse gases, ratcheting baseline temperatures upward.
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El Niño’s overlay: Natural cycles like El Niño add temporary warmth on top of that higher baseline, juicing the extremes we feel in specific years.
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Regional circulation quirks: Weather patterns and ocean currents can pile heat into certain basins (e.g., the Mediterranean), turning background warming into intense marine heatwaves.
What hotter oceans do
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Storm potential: Warm water is hurricane fuel. While the number of storms varies with wind shear and dust, potential intensity rises as ocean heat rises—shorter ramp-ups and higher ceilings on wind speed and rainfall.
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Ecosystems under pressure: Prolonged heat drives mass coral bleaching, stresses kelp forests, and shifts fish migration, altering catches for coastal communities.
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Weather on land: Oceans steer the atmosphere; heat-laden basins can nudge jet streams and monsoons, tilting regions toward floods, droughts, or wildfires—the kind of extremes Europe and parts of Asia have faced repeatedly.
Cause → Effect, simply
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Cause: Rising greenhouse gases + El Niño.
Effect: Warmer baseline + spikes → broader, longer marine heatwaves. Cause: Hot seas.
Effect: Stronger storm potential, ecosystem stress, and knock-on weather extremes.
What to watch
Recovery depends on how quickly temperatures drop after El Niño fades—and whether mitigation keeps the baseline from stair-stepping higher again.
