Ocean surface warming

Average Global Sea Surface Temperatures

Average Global Sea Surface Temperature: 1880 - 2015

(Average Global Sea Surface Temperature, 1880–2015: USA Environmental Protection Agency. This graph was at “https:// www .epa.gov/climate-indicators/climate-change-indicators-sea-surface-temperature”.

  • The thick orange line shows “the average sea surface temperature of the world’s oceans” between 1880 and 2015.  
  • These temperatures have been rising since 1970.
  • The grey band shows the range of uncertainty in the data.

This increase in sea surface temperature is further strong evidence that the planet is warming.

See The Latest Ocean Heat Graph. (Click on “Learn more” under the “Ocean Heat” graph)

This Climate Dot US website reproduces trusted climate information that was once available on US government websites. The Trump administration fired climate scientists and trashed these government sites. These scientists created this website

The phytoplankton feedback loop

Plankton

Phytoplankton:

  • Play a crucial part in the global carbon cycle.
  • Transfer vast amounts of carbon dioxide from the atmosphere to the ocean, then into the deep ocean.
  • Produce up to half of the oxygen we breathe.
  • They are the base of the ocean food chain.
  • The population has dropped by about 40% since 1950.

When sea surface temperatures rise, this activates the “phytoplankton feedback cycle”, another cyclic sequence of cause-and-effect that tends to raise global air temperatures. (See Self-amplifying feedback loops on this website.)

Higher air temperaturesMore ocean surface heating
More carbon dioxide in the airLess nutrient upwelling
Less photosynthesis & Less carbon sinking to the ocean floorReduced phytoplankton population

Diagram: The feedback cycle increases temperatures and decreases the phytoplankton population

Over a period in which this amplifying cycle was dominant:

  • Higher global air temperatures tend to
  • warm the ocean surface, which tends to
  • reduce the upwelling of cold, heavy, nutrient-rich water, which tends to
  • reduce the population of phytoplankton, which tends to
  • reduce photosynthesis, and reduce carbon accumulation in the deep oceans, which tend to
  • increase carbon dioxide in the air and increase global warming, which tends to
  • increase air temperatures, and the cycle repeats.

Ocean heat waves

Extreme temperatures are destroying kelp, seagrass, and corals – with alarming impacts on humanity. The number of heatwaves affecting the planet’s oceans has increased sharply, killing swathes of sea life, much like wildfires on land that destroy colossal forest areas. The damage caused in these hotspots is also harmful to humans. Humans rely on the oceans for oxygen, food, storm protection and the removal of climate-warming carbon dioxide from the atmosphere.

(Heat-waves sweeping oceans like wildfires: The Guardian: 5 Mar 2019: Damian Carrington)

Ocean temperatures continue to rise.

In 2022, I wrote: Ocean temperature recording began in 1955. In 2022, we saw that our oceans were the hottest on record. Ocean temperatures have broken this record every year since 2017.

(Oceans’ hottest temperatures: The Guardian: 11 Jan 2022)

In 2018, the rate of ocean warming was equivalent to five Hiroshima-size atomic bombs exploding every second.

(Our Oceans broke heat records in 2018, and the consequences are catastrophic: The Guardian: 16 Jan 2019)

Loaded February 2019: Modified 5 July 2026