2023’s record-high ocean temperatures could become the norm if the earth warms to 3.0°C above pre-industrial levels, estimate climate scientists.

In a new study, researchers have used computer models to show how last year’s extreme ocean conditions are similar to what we would expect to experience in future.

Currently, global temperatures have risen by 1.2°C since the Industrial Revolution – due to increased burning of fossil fuels and the emission of greenhouse gases like carbon dioxide and methane. Our planet continues to pass through milestones in its meteorological history, and the effects are being felt worldwide.

New global temperature records were set each month from June-December in 2023, making it the hottest year on record – with unprecedented consequences for our oceans. 

From March 2023, the North Atlantic began to show extremely warm temperatures far exceeding anything seen in the past 40 years. Since May 2023, the sea ice extent in the Southern Ocean around Antarctica has been the smallest since records began in 1979. As of August 2023, the North Atlantic was about 1.4°C warmer than the 1982-2011 average. 

A team of researchers from the National Centre for Atmospheric Science, National Centre for Earth Observation, University of Reading, and Imperial College London have examined the causes of recent record-breaking ocean temperatures.

Dr Till Kuhlbrodt, a senior climate scientist at the National Centre for Atmospheric Science and University of Reading, led the team’s investigations.

Dr Kuhlbrodt explains how extreme ocean temperatures are warning us of a warming world:

“The extraordinary heat in the North Atlantic and missing sea ice in the Southern Ocean in 2023 tell us the oceans are sounding an alarm. We urgently need to understand exactly why parts of the ocean are warming rapidly so we can prepare for more frequent weather disruption across the planet. How often we get hit by more of these extremes hangs on figuring out what’s driving the Atlantic and Southern Oceans into uncharted territory.”

Oceans cover 71% of the Earth’s surface, and their uptake of heat is crucial in mitigating global warming. 

The new research reveals how the Earth’s energy imbalance is likely a key driver of extreme ocean temperatures. The planet is currently absorbing more than 1.9 watts per square metre more solar energy than it radiates back to space as heat.

The imbalance has grown fast over recent decades, mainly due to heat-trapping greenhouse gases from human activity. This increasing energy surplus is propelling ocean warming, with more than 90% of the excess energy accumulated by Earth being funnelled into the oceans.

Since 2016 the Atlantic Ocean has warmed faster than other ocean basins in the top 100 metres of ocean. The rapid Atlantic warming has coincided with a sharp decline in sea ice cover surrounding Antarctica – and climate scientists are suggesting the two may be linked. 

The research team emphasises the need to quantify how much the rapid Atlantic warming is impacting sea ice cover. Reliably attributing the oceanic and sea ice extremes will ensure climate models can accurately predict future extremes, which will inform mitigation policies and resilience measures across the globe.

Dr Kuhlbrodt adds: “We need more data from the Atlantic to conclusively tie the warming and disappearing ice trends to a shift in the pattern of ocean currents, but the signals point to a hidden climate connection between the poles.”