It’s Getting Hot in Here: Ocean temperatures are on the rise

GLOBAL— A new study conducted under Plos Climate published on Feb. 1 written by Kisei R. Tanaka, and Kyle S.Van Houtan found more than half of the planet’s ocean surface has regularly surpassed historical extreme heat thresholds starting in 2014.

The study concluded such excessive ocean temperatures, fueled by climate change, have become the “new normal.” These heat extremes threaten crucial marine ecosystems, including coral reefs, seagrass meadows, and kelp forests, altering their structure and function while jeopardizing their ability to provide sustenance to human communities.

 

 

Although 2014 was the first year where more than half of the ocean surpassed the threshold, this upward trend continued in the following years reaching 57 percent of the ocean by 2019, according to the study.

 

Scientists have analyzed sea surface temperatures over the last 150 years, from 1870-to 2019, which have risen because of global heating. They found that extreme temperatures occurring just two percent of the time a century ago have occurred at least 50 percent of the time across the global ocean since 2014.

 

“This is a superb paper,” said President and CEO of the Aquarium of the Pacific Peter Kareiva. “They [the authors] used ocean sea surface temperature data from 1870 to 2019. The data were broken up into temperatures for each month and every 1 degree by 1-degree grid cell of the ocean. This massive publicly available data set is reconstructed from instrument records and historical in situ measurements of surface water temperatures. From this long data series, the first isolated the global data just for the fifty years from 1870 to 1919. Think of that as baseline pre-high emissions and pre-global warming.”

 

Kareiva applauded the study and explained that from those fifty years, the study identified extreme heat events as temperatures for a particular grid cell and month as temperatures in the highest two percent of all temperatures ever recorded (essentially the hottest record for those fifty years).

 

“What they discovered is startling,” said Kareiva. “Extreme events which once only covered two percent of the ocean surface, as of 2019 now cover 57 percent of the global ocean surface. In other words, the new normal, where normal is defined as what occurs more frequently than 50 percent, in what was only one hundred years ago an extreme heatwave. So, you might say the new normal is that the ocean now has a fever. We tend to talk about average temperatures. A change of one degree in average temperature might not seem like much but associated with that increase in average temperature are also more frequent extreme events or heatwaves.”

 

Some hotspots have extreme temperatures that severely affect wildlife 90 percent of the time. More than 90 percent of the heat trapped by greenhouse gases is absorbed by the ocean, which plays a critical role in maintaining a stable climate.

 

Due to these ever-increasing heatwaves in the last few years, researchers have seen massive fish kills in Western Australia, plunging salmon populations in the Gulf of Alaska that led to as many as one million seabird deaths, altered ocean currents, shifts in species ranges in the ocean, and just last summer a massive die-off of clams, roughly 50 percent of the population and 40 percent of the oyster population in the Pacific Northwest, according to Kareiva.

 

In addition, oyster farms lost production and money because of this. Heatwaves also bleach coral, and sometimes the damage is so severe the reefs do not recover. Locally, researchers have seen the decline of bull kelp off the coast of Northern California, which is driven by heatwaves.

 

According to the study, the shift in temperatures identified by the researchers grew out of their initial exploration of the history of kelp forest changes throughout California. As part of that study, Van Houtan and his colleagues began quantifying and mapping out sea surface heat extremes, key stressors for kelp along California’s coast over the past century.

 

The authors said they later decided to expand their efforts beyond California to understand the frequency and location of extreme marine heat worldwide.

 

In doing so, Tanaka and Van Houtan used historical records to determine average temperatures for the ocean’s surface from 1870 to 1919, identifying the top 2 percent of temperature increases during that period as “extreme heat,” according to the study. Then they mapped extremes for the next century that followed to determine whether such events were becoming more frequent.

 

“Today, the majority of the ocean’s surface has warmed to temperatures that only a century ago occurred as rare, once-in-50-year extreme warming events,” Van Houtan said in a statement.

 

As confirmed by the increasing evidence that extreme heat has become the new normal throughout most of the ocean’s surfaces, Tanaka and Van Houtan stress the need to control emissions generated from fossil fuels which they constitute as “the driver of climate change.”

 

“These dramatic changes we’ve recorded in the ocean are yet another piece of evidence that should be a wake-up call to act on climate change,” said Van Houtan. “We are experiencing it now, and it is speeding up.”

 

Oceans are a critical element in understanding climate change. The oceans cover roughly 70 percent of the planet’s surface and absorb more than 90 percent of heat produced from global warming. This new study has been helpful for researchers to look at the surface temperatures and evaluate the increase in extreme heat at the ocean’s surface and the extreme heat that is increasing over time.

 

Kyle Van Houtan and the Monterey Bay Aquarium were unavailable for comment.