If you've taken a coastal dip during the Easter break, chances are the water felt warmer than expected for this time of year.
The Earth's mean sea surface temperature (SST) has been around 0.7 degrees Celsius above the 1982-2011 average for weeks and has exceeded daily record levels since the middle of March.
Preliminary satellite data from the National Oceanic and Atmospheric Administration (NOAA), shows the global mean ocean surface temperature peaked at 21.1C in early April, passing the old record of 21.0C from March 2016.
The data measures the average temperature of the ocean's surface, covering the majority of the world's ice-free oceans.
The global average typically peaks in March, before decreasing to November as the vast Southern Hemisphere waters cool following the autumn equinox.
While the Earth's average SST has dropped slightly in recent days, it is still 0.1C above the old April record, with further daily and monthly records possible in the near future.
Marine heatwaves across Australia and the globe
A daily SST map reveals the extent of the warming oceans, with the water temperature currently above average across most of the Pacific, Atlantic, and Indian oceans.
The warmest waters compared to normal are currently off the west coast of South America, sitting about 5C above the April average.
Waters surrounding Australia have been warmer than usual off almost every coastline this year, at times 3C above normal.
"Sea surface temperatures for March were 0.66C above the 1961-1990 average, equal fourth warmest on record … but the only area where March was the highest on record was a small area off the Pilbara coast," Bureau of Meteorology climate scientist Blair Trewin said.
The Tasman Sea off the NSW north coast was warm enough in February and March to theoretically support the formation of a Tropical Cyclone, although atmospheric conditions above the surface were unsuitable.
While east Australian waters have remained just below record levels in 2023, the Coral Sea was at near record highs in late 2022.
"For the central Great Barrier Reef region, the SSTs were potentially record-breaking over the period September-November 2022," CSIRO Environment research oceanographer Chris Chapman said.
Global ocean temperatures trending upwards
The recent record continues the climate change induced warming seen across the majority of earth’s oceans during the past few decades.
The joint Bureau of Meteorologist and CSIRO State of the Climate report in 2022 reported a 1.05C increase in SSTs in the Australian region since 1900, with eight of the 10 warmest years recorded since 2010.
Dr Chapman said there is "clear and unambiguous evidence" of rising water temperatures.
"Although ocean temperatures will not increase at the same rate everywhere, almost the entire near surface ocean will be affected by rising temperatures in the coming decades."
El Niño could lead to further warming
The possible emergence of El Niño in 2023 could boost ocean temperatures even further over the next year.
According to the CSIRO, El Niño tends to increase globally averaged SSTs and raise sea-levels, a La Niña does the opposite.
Dr Chapman said that while El-Niño, or La-Nina, might make warmer oceans temperatures more likely, it is a combination of factors such as the "flavour, strength, and timing" of the phase that help determine this rise.
"Along with what else is going on in the climate system at the time, will all play a role in what eventually occurs," Dr Chapman said.
Warmer temperatures often occur in the year of decay, the year following El Niño's peak.
This was evident in 2016 which saw global SST records broken, one year after a very strong El Niño in 2015.
