Record levels of greenhouse gases have caused “planetary scale changes on land, in the ocean and in the atmosphere”, a UN agency says in a report that shows the past eight years were the hottest ever recorded on Earth.

Global sea levels are rising at more than double the pace they did in the first decade of measurements from 1993 to 2002 and touched a new record high last year, the World Meteorological Organization (WMO) said on Friday 21^st April 2023 in its State of Global Climate 2022 report.

Ocean heating

According to the WMO report, ocean heat content reached a new observed record high in 2022.  Around 90% of the energy trapped in the climate system by greenhouse gases goes into the ocean, somewhat ameliorating even higher temperature increases but posing risks to marine ecosystems. Ocean warming rates have been particularly high in the past two decades. Despite continuing La Niña conditions, 58% of the ocean surface experienced at least one marine heatwave during 2022.

Earlier in April 2023,  the global sea surface hit a new record high temperature. It has never warmed this much, this quickly. Now further evidence was revealed in an important new study published last week.  Over the past 15 years, the Earth’s accumulated heat has increased by 50%, with most of the extra going into the oceans.

This is having real world consequences, the BBC reported – not only did the overall temperature of the oceans hit a new record in April this year, in some regions the difference from the long term was enormous.

What are the impacts of ocean warming?

The BBC stated that the average surface temperature of the world’s seas has increased by around 0.9C compared to preindustrial levels, with 0.6C coming in the last 40 years alone.

This is less than increases in air temperatures over the land – which have risen by more than 1.5C since preindustrial times. This is because much more energy is needed to heat water than land, and because oceans absorb heat far below their surface. Even this seemingly small average increase has significant real-world consequences.

• Loss of species: more frequent and intense marine heatwaves lead to mass mortality of sea life. This is particularly damaging for coral reefs.
• More extreme weather: increased heat in the upper ocean surface means hurricanes and cyclones can pick up more energy. This means they become more intense and longer-lasting.
• Sea-level rise: warmer waters take up more space – known as thermal expansion – and can greatly accelerate the melting of glaciers from Greenland and Antarctica that flow into the oceans. This raises global sea levels, increasing risks of coastal flooding.
• Less ability to absorb CO2: the oceans currently take up about a quarter of greenhouse gas emissions. Warmer waters have less ability to absorb CO2. If the oceans take up less CO2 in future, more would accumulate in the atmosphere – further warming the air and oceans.

This story has been compiled from extracts in Al Jazeera, BBC, UN World Meteorological Organization, Guardian, and Earth System Science Data.