The best of EcoWatch, right in your inbox. Sign up for our email newsletter!
The ocean is taking up twice as much heat now as it was just two decades ago, relative to pre-industrial times. According to new research, a third of that heat—and rising—is finding its way into the deep ocean below 700m, temporarily slowing warming at Earth’s surface.
That the oceans are warming isn’t a surprise to scientists—it’s what we would expect from rising greenhouse gases. The more surprising part is the speed at which it is taking place.
The new study, published yesterday in Nature Climate Change, says as much heat entered the oceans in the last 18 years as in the previous 130 years.
The new findings add to a growing body of research on the unseen impact of human activity on the oceans and the role they play in moderating the temperature we feel on Earth’s surface, say scientists not involved in the study.
A Brief History
The oceans take up more than 90 percent of the heat trapped by greenhouse gases. It follows, then, that we would look to the oceans in seeking the fingerprint of human-caused climate change.
Scientists have been studying the oceans for hundreds of years. The Challenger expedition in the 1870s was considered the first real oceanographic voyage, bringing back with it reams of data from previously unexplored parts of the world, from the ocean surface to the sea floor.
Scientists’ instruments have changed a lot over time, from lowering buckets over the sides of wooden ships to the global fleet of drifting floats we have today, known as the ARGO array. Separating real changes in ocean heating from artefacts of switching from old to new methods is one of the biggest challenges in understanding how the oceans have changed over time.
The new study begins by compiling several different sets of observational measurements, from the Challenger expedition right up to the present day.
These include ship-based surveys of the upper ocean down to 700m repeated every year since the 1960s, temperature data down to 2,000m collected by ARGO floats since 2005 and transects carried out by ships extending down to below 2,000m in some parts of the world.
The observational data are far from perfect. There are many areas with sparse data, which means reliably estimating changes to ocean heat content is difficult using observations alone.
To address this, the study compares the different observational datasets with simulations from climate models (CMIP5) used in the latest Intergovernmental Panel on Climate Change, forced with historically realistic levels of greenhouse gases, emissions from land use, changes in solar activity and the temporary cooling effect of volcanic eruptions.
On the whole, the observations compared well with the average from the model simulations at all depths considered (0-700m, 700-2000m and below 2,000m). And it was passing this reliability test that allowed the scientists to cast the models backwards and examine how heat content in the oceans today compares to pre-industrial times.
For the ocean as a whole, the authors find that 50 percent of the heat taken up since 1865 has occurred since 1997. In other words, the oceans have absorbed as much heat in the past 18 years as in the previous 130 years, the paper notes.
These new findings largely confirm what scientists already knew about human-induced climate change, says Dr. Matt Palmer from the Met Office Hadley Center:
"This research shows the strengthening of the climate change signal over time and that more of this signal is finding its way into the deep ocean."
The study also confirms that while temperatures at Earth’s surface have risen more slowly over the past 10-15 years than in previous decades—a familiar feature if you look back at Earth’s full temperature record—there has been no such change of pace in the oceans. Palmer adds:
"[The study] confirms that ocean heat uptake has been proceeding at the expected rate—the ‘hiatus’ is a surface phenomenon. The Earth is still warming and the oceans have been taking up the bulk of that heat."
The novel part of today’s study comes in the comparison of observations with climate models—particularly below 700m—and the comparison of ocean heat content now with preindustrial times. Scientists’ interest in studying the deep ocean has been driven partly by a wish to understand the behaviour of surface temperatures in recent times but mostly by advances in the ways available to monitor ocean temperature, says Palmer.
There is still some work to do in pinning down exactly how much heat the oceans have taken up in the past two decades and whether that can account for the whole so-called slowdown in surface warming, the paper notes. That’s not as straightforward as it sounds, largely because of how to account for the transition to ARGO floats from traditional methods, the paper notes.
Another point to note is that the climate models used do not include volcanic eruptions after 2000, which the authors estimate could offset the rise in global temperature by around 7 percent.
While the oceans seem to have slowed warming at the Earth’s surface in recent decades, this shouldn’t be interpreted as a good thing, says Prof. John Shepherd from the National Oceanography Center in Southampton. He says:
"Once the ocean heat uptake settles down again, the rate of warming is likely to return to what it was before."
How the ocean acts to moderate surface temperatures is vital for understanding how our planet responds to greenhouse gases over the long term, a concept known as the “climate sensitivity." The mechanisms and timescales at play are critical pieces of that ongoing puzzle.
YOU MIGHT ALSO LIKE
EcoWatch Daily Newsletter
Tensions are continuing to rise in Canada over a controversial pipeline project as protesters enter their 12th day blockading railways, demonstrating on streets and highways, and paralyzing the nation's rail system
Colorado River Has Lost 1.5 Billion Tons of Water to the Climate Crisis, 'Severe Water Shortages' May Follow
California is headed toward drought conditions as February, typically the state's wettest month, passes without a drop of rain. The lack of rainfall could lead to early fire conditions. With no rain predicted for the next week, it looks as if this month will be only the second time in 170 years that San Francisco has not had a drop of rain in February, according to The Weather Channel.
The last time San Francisco did not record a drop of rain in February was in 1864 as the Civil War raged.
"This hasn't happened in 150 years or more," said Daniel Swain, a climate scientist at UCLA's Institute of the Environment and Sustainability to The Guardian. "There have even been a couple [of] wildfires – which is definitely not something you typically hear about in the middle of winter."
While the Pacific Northwest has flooded from heavy rains, the southern part of the West Coast has seen one storm after another pass by. Last week, the U.S. Drought Monitor said more Californians are in drought conditions than at any time during 2019, as The Weather Channel reported.
The dry winter has included areas that have seen devastating fires recently, including Sonoma, Napa, Lake and Mendocino counties. If the dry conditions continue, those areas will once again have dangerously high fire conditions, according to The Mercury News.
"Given what we've seen so far this year and the forecast for the next few weeks, I do think it's pretty likely we'll end up in some degree of drought by this summer," said Swain, as The Mercury News reported.
Another alarming sign of an impending drought is the decreased snowpack in the Sierra Nevada Mountain range. The National Weather Service posted to Twitter a side-by-side comparison of snowpack from February 2019 and from this year, illustrating the puny snowpack this year. The snow accumulated in the Sierra Nevadas provides water to roughly 30 percent of the state, according to NBC Los Angeles.
Right now, the snowpack is at 53 percent of its normal volume after two warm and dry months to start the year. It is a remarkable decline, considering that the snowpack started 2020 at 90 percent of its historical average, as The Guardian reported.
"Those numbers are going to continue to go down," said Swain. "I would guess that the 1 March number is going to be less than 50 percent."
The National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center forecast that the drier-than-average conditions may last through April.
NOAA said Northern California will continue deeper into drought through the end of April, citing that the "persistent high pressure over the North Pacific Ocean is expected to continue, diverting storm systems to the north and south and away from California and parts of the Southwest," as The Weather Channel reported.
As the climate crisis escalates and the world continues to heat up, California should expect to see water drawn out of its ecosystem, making the state warmer and drier. Increased heat will lead to further loss of snow, both as less falls and as more of it melts quickly, according to The Guardian.
"We aren't going to necessarily see less rain, it's just that that rain goes less far. That's a future where the flood risk extends, with bigger wetter storms in a warming world," said Swain, as The Guardian reported.
The Guardian noted that while California's reservoirs are currently near capacity, the more immediate impact of the warm, dry winter will be how it raises the fire danger as trees and grasslands dry out.
"The plants and the forests don't benefit from the water storage reservoirs," said Swain, as The Mercury News reported. "If conditions remain very dry heading into summer, the landscape and vegetation is definitely going to feel it this year. From a wildfire perspective, the dry years do tend to be the bad fire years, especially in Northern California."
- Is California heading for another drought? - Los Angeles Times ›
- CA wildfire season: Will rain, snow weather forecast end risk? | The ... ›
- California Fires Now Rage All Year as Drought Creates Tinderbox ... ›
- California weather stays dry as rain and snow come up short | The ... ›
- California Emerged From Drought and Is Still Catching Fire - The ... ›
A warm day in winter used to be a rare and uplifting relief.
Now such days are routine reminders of climate change – all the more foreboding when they coincide with news stories about unprecedented wildfires, record-breaking "rain bombs," or the accelerated melting of polar ice sheets.
Where, then, can one turn for hope in these dark months of the year?