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How do we know the ocean is getting hotter?
Each bar is one year (0–700 m of global ocean). Color = heat anomaly vs the 1955–1990 baseline (blue = cooler, red = hotter). The numbers above are in zettajoules of extra heat stored — seven decades of almost unbroken red.
Every year since 2005, drawn on top of each other
Each thin grey line is one calendar year of monthly ocean-heat values (top 2 km). The bold red line is the latest year — clearly above everything that came before.
Source: China’s Institute of Atmospheric Physics (IAPv4.2), monthly. Rebased to the same 2005–2009 starting point as the chart below.
Where is the heat going? Pacific, Atlantic, Indian, World
Each row: one ocean basin, one bar per year (0–2000 m). Same color scale across all four — scan for which basin is reddest lately.
How fast is heat building up? Top 2 km of ocean
Extra heat stored vs NOAA’s baseline — reliable from ~2005 when deep measurements were dense enough.
How much energy is that?
Why does this matter? The cascade
About 90% of the heat trapped by greenhouse gases ends up here, in the ocean — not in the air you feel. Ocean heat is the upstream cause; everything below is happening right now, all at the same time.
Ocean stores ~90% of greenhouse heat (the engine) — Earth’s main heat bank, hard to reverse on human timescales.
The direct sea-level chain
- Water warms and expands Thermal expansion is the largest single contributor to global sea-level rise, ahead of melting ice.
- Sea level rises Global mean sea level has risen about 24 cm since 1880 and is accelerating; expansion plus ice-shelf melt together drive the trend.
- Coastal cities flood more often Higher baseline seas turn ordinary high tides and storms into damaging surges.
Other impacts happening at the same time
- Marine heatwaves Heatwave days at sea have risen about +54% per century — roughly twice as frequent as the early 1980s.
- Coral reefs bleach Sustained surface heat pushes reefs past their survival threshold; mass-bleaching events have hit every ocean basin since 2023.
- Hurricanes intensify Warm upper-ocean water powers tropical cyclones; rapid intensification near landfall has become noticeably more common over the past 40 years.
- Less oxygen in the water Warmer water holds less dissolved oxygen; the global ocean has lost about 2% of its oxygen since 1960, squeezing fish and squid habitat.
- Fish move toward the poles Marine species are shifting their range by about 70 km per decade on average, reshaping fisheries and food security.
- Antarctic ice shelves melt from below Warm subsurface water reaches the underside of ice shelves like Thwaites and accelerates their breakup — a second route into sea-level rise.
Each linked tile opens its own live dashboard — click through to see the latest numbers.
Ocean heat in the news
How we know this
- Source: NOAA NCEI global ocean heat content (official climate data record).
- Update cadence: We refresh from NOAA’s public files daily; new calendar years appear when NOAA publishes them (a few times per year).
- Time coverage: Stripes and cumulative total use 0–700 m from 1955; the line chart uses 0–2000 m from ~2005.
- Methods: Basin and global anomalies vs NOAA’s baseline — not a live buoy feed.
- Uncertainty: Year-to-year wiggles are real; the multi-decade warming direction is robust. Other research groups can differ by ~10% on totals.
- Limitations: Deep ocean before ~2005 is less certain; comparison icons are illustrative only.
- Primary data: NOAA NCEI ocean heat content · How this page is built