»Meerestemperatur weiter auf Rekordniveau«

Studie einer internationalen Forschergruppe im Journal "Advances in Atmospheric Sciences" (engl. Originalfassung), 14.1.2020

Human-emitted greenhouse gases (GHGs) have resulted in a long-term and unequivocal warming of the planet. Because the oceans are the main repository of the Earth’s energy imbalance, measuring ocean heat content is one of the best way to quantify the rate of global warming. These data reveal that the world’s oceans (especially at upper 2000 m) in 2019 were the warmest in recorded human history. 

The ocean heating is irrefutable, and a key measure of the Earth’s energy imbalance: the excess GHGs in the air trap more heat inside the climate system and drives global warming. More than 90% of the heat accumulates in the ocean because of its large heat capacity, and the remaining heating manifests as atmospheric warming, a drying and warming landmass, and melting of land and sea ice. According to the altimetry satellite record, the past 10 years are also the highest in global mean sea level since 1900.

Increases in ocean temperature reduce dissolved oxygen in the ocean and significantly affect sea life, particularly corals. The increasing heat increases evaporation, and the extra moisture in the warmer atmosphere nourishes heavy rains and promotes flooding, leading to a more extreme hydrological cycle and more extreme weather (in particular hurricanes and typhoons). It is one of the key reasons why the Earth has experienced increasing catastrophic fires in the Amazon, California, and Australia in 2019 (extending into 2020 for Australia). 

It is important to note that ocean warming will continue even if the global mean surface air temperature can be stabilized at or below 2°C (the key policy target of the Paris Agreement). This means that the ocean (and the large ice sheets) are slow to respond and equilibrate, and will continue to change even after radiative forcing stabilizes. However, the rates and magnitudes of ocean warming will be smaller with lower GHG emissions. Hence, the rate of increase can be reduced by appropriate human actions that lead to rapid reductions in GHG emissions, thereby reducing the risks to humans and other life on Earth.

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