Spike in ocean heat stuns scientists: Have we breached a climate tipping point?
TAMPA, Fla. (WFLA) — Global oceans are so hot right now, scientists all around the world are struggling to explain the phenomenon. Sea surface temperatures in June are so far above record territory it is being deemed almost statistically impossible in a climate without global heating.
This is happening across the huge expanse of the Pacific and Atlantic Oceans.
In the North Atlantic Ocean — which was already way above record levels — temperatures have strikingly shot directly upward over the past two weeks.
A shocking visual shared on Twitter earlier this month is prompting many to ask whether this recent surge is evidence that human-caused heating has propelled the climate past a tipping point.
Luckily, climate scientists say the answer is likely no. Instead, it is much more probable to be a compounding coalescence of various factors – some natural and some human-caused. In other words, a coincidence of natural factors piled on top of the steady trend of human-caused global heating.
Regardless it’s a vivid illustration of the new extremes Earth can reach when conditions are ripe.
Ocean temperatures in any given region are the result of complex interactions between ocean currents, weather, climate oscillations and longer-term climate trends. In the case of this year, there are many factors, but the biggest factor is the change from La Niña to El Niño in the Tropical Pacific Ocean – a natural cycle that has global implications.
For the past three years, Earth has been in a rare prolonged La Niña event. During that time, heat piled up in the tropical Western Pacific Ocean near Indonesia. But this spring, subsurface heat started propagating eastward across the Pacific Ocean and reached the surface. This marked the beginning of the warm phase called El Niño.
With warm water now sitting on the surface of the entire Tropical Pacific Ocean – a particularly wide swath of the ocean basin – Pacific Ocean temperatures have been rising fast.
But the effects of El Niño are not confined to the Pacific Ocean. The ocean-air heat exchange results in changes in the atmospheric steering flow and pressure systems in the Atlantic as well. These changes in weather over the Atlantic Ocean, some related to El Niño, can have significant impacts on surface ocean temperatures.
At the same time, in the high latitudes of Canada and the far North Atlantic, a very blocked jet stream pattern has persisted for weeks. These persistent weather patterns have a significant impact on the underlying sea surface temperatures. Areas where it is sunny and calm tend to warm up and cloudy, windy areas tend to cool.
Canada has been trapped under a heat dome leading to record-setting wildfires and the US eastern seaboard/ western Atlantic has been stuck under the opposite — a cool dip in the jet stream. And over on the other side of the Atlantic, an ocean heat dome has been present near Europe.
The result of this stubborn configuration is a cooler-than-normal NW Atlantic and a much warmer-than-normal NE Atlantic.
To the south across the Tropical Atlantic, this odd and persistent configuration of atmospheric steering and pressure systems has resulted in record-shattering heat. Sea surface temperatures are so hot across the “main development region” (seen in deep red between Africa and the Caribbean on this map) they have already reached levels expected during peak hurricane season in September.
To be more specific, this excess heat can be explained by some interrelated factors. Atmospheric high pressure over the Subtropical Atlantic is weaker than normal, likely due to a combination of the odd North Atlantic steering discussed above, and also El Niño’s influence, weakening the tropical winds called trade winds.
These trade winds blow across the deep tropical Atlantic from east (Africa) to west (Caribbean). When they are strong the waters cool due to increased upwelling of cooler water from below and also increased evaporation. This season, however, the weaker high pressure and lighter trade winds are helping increase sea surface temperatures.
Weaker trade winds usually also correspond to less Saharan dust coming off of Africa. This year, dust is at a record low. Less dust means cleaner air, allowing more sun to reach and heat the ocean surface.
From the above, we can see the various ways persistent weather patterns can shape ocean temperatures around the globe. But there are a few more underlying reasons for the record warm departures in ocean surface temperature.
The most obvious is greenhouse warming. This did not cause the recent spike, but it is a big reason we are able to so easily achieve record territory nowadays.
In general, the oceans have warmed around 2 degrees Fahrenheit since the early 1900s. This is the elevated baseline/ foundation which everything else is built upon.
If you compare June ocean temperatures in the 1982 El Niño — which eventually became one of the strongest ever — to June 2023 you can easily see the stark difference. This year is far and away much warmer across global oceans. That is mainly due to a trend in human-caused greenhouse warming.
But there’s more. Over the past few decades atmospheric pollution, especially across the North Atlantic, has lessened due to the Clean Air Act. Airborne pollution decreases the amount of sunlight reaching the Earth and helps cool us, masking some of the greenhouse warming. But as pollution has decreased in recent decades the Atlantic ocean temperatures have increased.
One very prominent example of this is very recent. In 2020, cargo ships, which traditionally burned the dirtiest of fuel, were forced to substantially reduce Sulphur dioxide (SO2) emissions. Now, cargo ships are running much cleaner. The reduction in pollution, which is otherwise good news, means an increase in ocean heating.
In this graph, you can see the dramatic drop in SO2 in the last 2 years. The jury is still out on how much this is contributing to ocean heating.
Lastly, we should address a real wildcard. In January 2022, the underwater Hunga Tonga Volcano erupted in the South Pacific Ocean. The resulting explosion spewed large amounts of water vapor high up into the atmosphere where it still lingers.
This water vapor cools the upper atmosphere but warms Earth’s surface. It is an unexpected natural phenomenon.
So, it is clear from the analysis above that there is not one culprit for the ocean’s uncanny warmth. Instead, it seems like the unfortunate coincidence of various factors, both natural and human. If this logic is correct, then this perturbation is not evidence of humans tripping a climate tipping point, for now.
But as 2023 unfolds, El Niño will continue to intensify in the Pacific, infusing the climate system with even more energy. On top of global heating, this will supercharge global weather patterns yielding extremes modern man has yet to experience.
And as global heating persists in the coming decades, tipping points may very well be breached in the climate system, causing irreversible impacts.
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