2019 was the third year in a row to set a new record in ocean temperatures. The heating of the oceans is highly concerning, as it shows even more clearly than the air temperatures how the climate crisis is escalating. The oceans absorb most of the heat that the greenhouse gases trap. In addition, the ocean temperatures are less affected by natural variations than surface temperatures are, making ocean data more reliable. The fact that the last 10 years are all among 10 years with the highest temperature on the record shows even better that global warming is undeniable. Even more concerning is that the speed of ocean warming has increased by 500% since 1980s.
Please also read: Weather extremes versus climate overheating
Although ocean temperatures may seem less relevant to us as a terrrestrial species than surface temperatures, oceans have a strong regulatory role in Earth’s climate. Hot oceans lead to more frequent and more severe storms. For example, a hotspot in the Gulf of Mexico produced Hurricane Harvey that killed dozens of people and caused over a hundren billion dollars of damage. Besides, hotter oceans disrupt the water cycle, leading to more droughts, floods and wildfires. Warmer oceans also speed up the ice melt. This causes an even faster sea level rise that is already threatening hundreds of millions of people.
Effects of ocean heating on biodiversity
Ocean warming also has a catastrophic effect on marine wildlife. Many marine species cannot survive the increasingly frequent heatwaves. This leads to mass die-offs of fish, such as the chinook salmon in 2019. Besides, coral bleaching due to warmer oceans has catastrophic consequences for the most diverse marine ecosystems, coral reefs. Even species such as whales are under strong impact of climate change, as their food, the krill, are in decline as a result. Unfortunately, the ocean is heating fastest up to 300 m in depth, which is also the part where most life occurs. Due to greenhouse gas emissions, the oxygen level and the pH of the oceans are also changing. This leads to more and more parts of the ocean becoming inhospitable for life.
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