Last year was the hottest for the planet's oceans since global records began in 1958, according to an international team of scientists who track the data. Their findings were published Wednesday in the scientific journal Advances in Atmospheric Sciences.
The year 2018 passed the previous record set just the year before, in 2017; the top five years of ocean heat have come in the last five years. Last year continues a startling trend of global ocean warming that is a direct result of humans' warming of the planet, the authors say.
The same group of scientists published a study last week showing that oceans are warming faster than scientists thought, by absorbing more heat than was previously known. That will result in a six-fold increase in ocean warming by 2081-2100, compared to the past 60 years.
Warmer oceans lead to a variety of problems, such as sea level rise, more intense storms with heavier rainfall, coral bleaching and melting polar ice.
The increasing amount of heat-trapping gases, such as carbon dioxide, released into the atmosphere by humans, creates an energy imbalance that leads to global heating.
"The vast majority of global warming heat ends up deposited in the world's oceans," the authors say, which make it one of the best -- if not the best -- indicator for climate change. In fact, studies show over 90% of the heat trapped by greenhouse gases gets absorbed in the ocean.
"Increases in ocean heat are incontrovertible proof that the Earth is warming," the study said.
Ocean heat shows proof of global warming
Kevin Trenberth, a scientist with the Climate Analysis Section at the US National Center for Atmospheric Research and co-author of the study, said the ocean heat trend is a better climate change indicator than air temperature.
"The global mean surface temperature record is greatly affected by weather, El Nino and so forth," Trenberth said. "The ocean heat warming signal is much more visible and not as noisy."
Impacts from the warmer oceans
The impacts from warming oceans were clearly visible during the past year, according the study's authors.
The added heat resulted in a global mean sea level rise of 29.5 millimeters above the 1981-2010 average, which was the largest ever observed. Rising sea levels makes coastal communities more susceptible to storm surges, coastal erosion and saltwater intrusion of freshwater supplies.
Warmer water fueled a number of major hurricanes and typhoons across the world in 2018, including hurricanes Michael and Florence, which brought massive wind destruction and devastating floods to the US Southeast, and Super Typhoon Mangkhut, the strongest storm of the year, which caused major damage to the Philippines and Hong Kong.
The warmer water also allows the air to hold more moisture, which supercharged the rainfall from Hurricane Florence in the Carolinas. Warmer than normal ocean waters in the Pacific in Indian Ocean also fed major flooding events in Japan and India.
Other impacts from the warmer oceans include bleaching and death of coral reefs, which have been significant in recent years in the Great Barrier Reef off of Australia.
Melting sea ice and ice shelves are another by product of the added heat in the oceans, and can also add to sea level rise as land ice flows into the ocean. An unrelated study released earlier this week found that warmer ocean temperatures have been melting Antarctic ice at a rapidly accelerating rate.
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