Pattern of ocean warming persists
Earth’s oceans are taking a hit for the planet but the reckoning is coming, writes Tony Barboza , of the Los Angeles Times.
EARTH’S oceans had their warmest year on record in 2018, a stark indication of the enormous amount of heat being absorbed by the sea as greenhouse gas emissions continue to rise, scientists reported last week.
The analysis by an international team of scientists confirms the oceans are heating up much faster than previously recognised and the pace of warming has accelerated sharply since the 1990s.
Rising ocean temperatures are already having profound consequences across the globe, scientists say, contributing to more intense hurricanes, destroying coral reefs and causing sea levels to rise.
The report in the journal Advances in Academic Sciences builds on a study published the previous week that found oceans are warming 40% more, on average, than was estimated by a United Nations scientific panel just five years ago. In fact, each of the past 10 years is among the 10 warmest on record, according to data from Lijing Cheng, of the Institute of Atmospheric Physics in Beijing, who led the research.
The unrelenting pattern is ‘‘incontrovertible proof that the Earth is warming’,’ the authors of the new study wrote.
Earth’s oceans provide a crucial buffer against climate change by swallowing 93% of the excess heat trapped by the greenhouse gases humans are spewing into the atmosphere.
‘‘The oceans are really the earth’s thermometer,’’ said Zeke Hausfather, a climate scientist with academic nonprofit Berkeley Earth who collaborated on the research.
‘‘They’re where all the heat ends up. They’re where we’d expect the strongest signs of climate change to be. And that’s exactly what we see.’’
In contrast with rising surface temperatures, which can vary from year to year with the influence of weather and cyclical climate patterns such as El Nino, the warming of the ocean has been inexorable; virtually every year has broken the heat record set just 12 months earlier.
‘‘There’s no sign of any slowdown or pause,’’ Hausfather said.
‘‘The ocean temperature is increasing year over year in lockstep with increases in atmospheric carbon dioxide and other greenhouse gases.’’
Indeed, emissions have accelerated as President Donald Trump and some other world leaders have pursued energy policies that promote fossil fuels.
Global carbon emissions increased 1.6% from 2016 to 2017, then jumped an additional 2.7% in 2018, according to estimates published last month in the journal Environmental Research Letters. Earlier this month, research firm Rhodium Group reported that US carbon emissions rose 3.4% in 2018 after years of declines.
Rather than measure the water’s temperature, the researchers focused on the amount of energy the oceans had taken in. They determined the heat content had increased by around 370 zettajoules (1ZJ = 1021 joules) since 1955. The increase in 2018 alone compared with 2017 — about 9ZJ — was about 100 million times greater than the heat released by the atomic bomb dropped on Hiroshima, Japan, Hausfather said.
The rate of warming in the ocean’s upper 1980m has been up to five times faster since 1991 than it was in the 1970s and ’80s, scientists found. The warming is more pronounced in shallower waters, about twothirds of the energy accumulating within
610m of the surface.
The effects will grow more devastating the longer oceans continue to warm, scientists say. Wetter, more powerful hurricanes, like Harvey in 2017, will become more frequent. Marine ecosystems, including coral reefs already stressed by past warming, will be unable to recover from marine heat waves and bleaching.
Oceans cover 71% of the
Earth’s surface, but the heat they contain is distributed unevenly. In 2018, one of the warmest spots was along the East Coast of the United States, where Hurricane Florence caused severe flood damage in the Carolinas last autumn.
Warming ocean waters have had a direct influence on storms such as Florence and Harvey, scientists said, feeding them more energy and allowing them to hold more water vapour that rains down on coastal communities.
Ocean warming is also the main driver of the rising sea levels that are threatening coastal communities and ecosystems and causing more severe flooding.
Without global action to slash greenhouse gas emissions, the study projects, the planet could see about another foot of sea level rise just from warmer water taking up more space.
That socalled thermal expansion does not factor in additional increases expected as ice sheets melt in Greenland and the Antarctic.
Lisa Suatoni, a marine ecologist at the Natural Resources Defence Council, said the warming detected to date was already causing rapid transformation of ocean ecosystems, including certain marine species moving towards the poles and economically harmful disruptions to fisheries.
‘‘The ocean is playing this silent but important service to the earth in absorbing most of the heat that’s being trapped by our greenhouse gas emissions, but that service comes at a cost,’’ Suatoni said.
‘‘The transformation that global warming is having on the oceans is largely unseen because we’re land animals and it’s hard to observe.’’
That is changing. Scientists’ observations are improving considerably thanks to new measurement techniques, particularly Argo, a network of drifting, automated floats in operation since the mid2000s that periodically descend into the ocean to measure temperature and salinity, then transmit the readings to satellites.
The new analysis is based on Argo’s measurements of the upper 1980m of the ocean combined with earlier readings that go back to the 1950s. Scientists compared four different estimates of ocean warming completed since the United Nations’ Intergovernmental Panel on Climate Change report in 2014 and found them converging in agreement: Oceans were warming faster than previous estimates. — TNS
❛ The ocean is playing this silent but important service to the earth in absorbing most of the heat . . . but that service comes at a cost