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.
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EcoWatch Daily Newsletter
By Mark Hertsgaard
What follows are not candidate endorsements. Rather, this nonpartisan guide aims to inform voters' choices, help journalists decide what races to follow, and explore what the 2020 elections could portend for climate action in the United States in 2021 and beyond.
Will the White House Turn Green?<p>Whether the White House changes hands is the most important climate question of the 2020 elections. President Donald Trump rejects climate science, is withdrawing the United States from the Paris Agreement, and has accelerated fossil fuel development. His climate policy seems to be, as he tweeted in January when rejecting a U.S. Army Corps of Engineers proposal to protect New York City from storm surges, "Get your mops and buckets ready."</p><p>Joe Biden, who started the 2020 campaign with a climate position so weak that activists gave it an "F," called Trump a "climate arsonist" during California's recent wildfires. Biden backs a $2 trillion plan to create millions of jobs while slashing emissions—a Green New Deal in all but name. Equally striking, his running mate, California Senator Kamala Harris, has endorsed phasing out fossil fuel production—a politically explosive scientific imperative.</p><p>The race will be decided in a handful of battleground states, five of which already face grave climate dangers: Florida (hurricanes and sea-level rise), North Carolina (ditto), Texas (storms and drought), Michigan (floods), and Arizona (heat waves and drought). <a href="https://climatecommunication.yale.edu/visualizations-data/ycom-us/" target="_blank">Public concern is rising</a> in these states, but will that concern translate into votes?</p>
Will Democrats Flip the Senate, and by Enough to Pass a Green New Deal?<p>With Democrats all but certain to maintain their majority in the U.S. House of Representatives, the Senate will determine whether a potential Biden administration can actually deliver climate progress. Democrats need to pick up three seats to flip the Senate if Biden wins, four if he doesn't. But since aggressive climate policy is shunned by some Democrats, notably Joe Manchin of coal-dependent West Virginia, Democrats probably need to gain five or six Senate seats to pass a Green New Deal.</p><p>Environmentalists, including the League of Conservation Voters, are targeting six Republicans who polls suggest are vulnerable.</p><ul><li>Steve Daines of Montana, who denies climate science</li><li>Martha McSally of Arizona</li><li>Thom Tillis of North Carolina</li><li>Susan Collins of Maine</li><li>Joni Ernst of Iowa (bankrolled by Charles Koch)</li><li>John James of Michigan (also a Koch beneficiary)</li></ul><p>Republican Senators are even at risk in conservative Kansas and Alaska. In both states, the Democratic candidates are physicians—not a bad credential amid a pandemic—who support climate action. In Kansas, Barbara Bollier faces an incumbent funded by Charles Koch. In Alaska, Al Gross urges a transition away from oil, though his openness to limited drilling in the Arctic National Wildlife Preserve dims his appeal to green groups. He faces incumbent Republican Dan Sullivan, who receives an 8 percent lifetime voting record from the League of Conservation Voters.</p>
Will Local and State Races Advance Climate Progress?<h4>THE CLIMATE HAWKS</h4><p>Under Democratic and Republican leadership alike, Washington has long been a graveyard for strong climate action. But governors can boost or block renewable energy; the Vermont and New Hampshire races are worth watching. Attorneys general can sue fossil fuel companies for lying about climate change; climate hawks are running for the top law enforcement seats in Montana and North Carolina. State legislatures can accelerate or delay climate progress, as the new Democratic majorities in Virginia have shown. Here, races to watch include Pennsylvania, North Carolina, and Colorado.</p><h4>THE CLIMATE POLICY MAKERS</h4><p>Perhaps the most powerful, and most overlooked, climate policy makers are public utility commissions. They control whether pipelines and other energy infrastructure gets built; they regulate whether electric utilities expand solar and energy efficiency or stick with the carbon-heavy status quo. Regulatory capture and outright corruption are not uncommon.</p><p>A prime example is Arizona, where a former two-term commissioner known as the godfather of solar in the state is seeking a comeback. Bill Mundell argues that since Arizona law permits utilities to contribute to commissioners' electoral campaigns, the companies can buy their own regulators. Which may explain why super-sunny Arizona has so little installed solar capacity.</p><p>In South Dakota, Remi Bald Eagle, a Native American U.S. Army veteran, seeks a seat on the South Dakota Public Utilities Commission, which rules on the Standing Rock oil pipeline. And in what <em>HuffPost</em> called "the most important environmental race in the country," Democrat Chrysta Castaneda, who favors phasing out oil production, is running for the Texas Railroad Commission, which despite its name decides what oil, gas, and electric companies in America's leading petro-state can build.</p>
Will the Influencers Usher in a Green New Era?<h4>THE UNCOUNTED</h4><p>The story that goes largely under-reported in every U.S. election is how few Americans vote. In 2016, some 90 million, <a href="https://www.pewresearch.org/politics/2018/08/09/an-examination-of-the-2016-electorate-based-on-validated-voters/" target="_blank" rel="noopener noreferrer">roughly four out of every 10 eligible voters</a>, did not cast a ballot. Attorney Nathaniel Stinnett claims that 10 million of these nonvoters nevertheless identify as environmentalists: They support green policies, even donate to activist groups; they just don't vote. Stinnett's <a href="https://www.environmentalvoter.org/" target="_blank" rel="noopener noreferrer">Environmental Voter Project</a> works to awaken this sleeping giant.</p><h4>THE SUNRISE MOVEMENT</h4><p>Meanwhile, the young climate activists of the <a href="http://www.sunrisemovement.org/" target="_blank" rel="noopener noreferrer">Sunrise Movement</a> are already winning elections with an unabashedly Green New Deal message. More than any other group, Sunrise pushed the Green New Deal into the national political conversation, helping Representative Alexandria Ocasio-Cortez and Senator Ed Markey draft the eponymous congressional resolution. In 2020, Sunrise has helped Green New Deal champions defeat centrists in Democratic primaries, with Markey dealing Representative Joe Kennedy Jr. the first defeat a Kennedy has ever suffered in a Massachusetts election. But can Sunrise also be successful against Republicans in the general elections this fall?</p><h4>THE STARPOWER</h4><p>And an intriguing wild card: celebrity firepower, grassroots activism, and big-bucks marketing have converged behind a campaign to get Latina mothers to vote climate in 2020. Latinos have long been the U.S. demographic most concerned about climate change. Now, <a href="https://votelikeamadre.com/" target="_blank" rel="noopener noreferrer">Vote Like A Madre</a> aims to get 5 million Latina mothers in Florida, Texas, and Arizona to the polls. Jennifer Lopez, Salma Hayak, and Lin-Manuel Miranda are urging mothers to make a "pinky promise" to vote for their kids' climate future in November. Turning out even a quarter of those 5 million voters, though no easy task, could swing the results in three states Trump must win to remain president, which brings us back to the first category, "Will the White House Turn Green?"</p>
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By Tony Carnie
South Africa is home to around 1,300 of the world's roughly 7,100 remaining cheetahs. It's also the only country in the world with significant cheetah population growth, thanks largely to a nongovernmental conservation project that depends on careful and intensive human management of small, fenced-in cheetah populations. Because most of the reserves are privately funded and properly fenced, the animals benefit from higher levels of security than in the increasingly thinly funded state reserves.
Vincent van der Merwe at a cheetah translocation. Endangered Wildlife Trust
Under Pressure<p>Cheetah populations elsewhere in Southern Africa have not prospered over the past 50 years. In Zimbabwe, cheetah numbers have crashed from 1,500 in 1975, to just 170 today. Botswana's cheetah population has held steady at around 1,500 over the same period, but illegal capture for captive breeding and conflicts with farmers and the growing human population are increasing. In Namibia, there were an estimated 3,000 cheetah in in 1975; roughly 1,400 remain today.</p><p>In contrast, South Africa's cheetah numbers have grown from about 500 in 1975 to nearly 1,300 today. Van der Merwe, who is also a Ph.D. student at the University of Cape Town's Institute for Communities and Wildlife in Africa (iCWild), says he's confident that South Africa will soon overtake Namibia and Botswana, largely because the majority of South African cheetahs are protected and managed behind fences, whereas most of the animals in the neighboring countries remain more vulnerable on mainly unfenced lands.</p><p>Wildlife researchers Florian Weise and colleagues have reported that private stock owners in Namibia still trap cheetahs mainly for translocation, but there are few public or private reserves large enough to contain them. Weise says that conservation efforts need to focus on improving tolerance toward cheetahs in commercial livestock and game farming areas to reduce indiscriminate trapping.</p><p>Van der Merwe says fences can be both a blessing and a curse. While these barriers prevent cheetahs and other wild animals from migrating naturally to breed and feed, they also protect cheetahs from the growing tide of threats from humanity and agriculture.</p><p>To simulate natural dispersion patterns that guard against inbreeding, the trust helps landowners swap their animals with other cheetah reserves elsewhere in the country. The South African metapopulation project has been so successful in boosting numbers that the trust is having to look beyond national boundaries to secure new translocation areas in Malawi, Zambia and Mozambique.</p><p>Cheetah translocations have been going on in South Africa since the mid-1960s, when the first unsuccessful attempts were made to move scores of these animals from Namibia. These relocations were mostly unsuccessful.</p>
Charli de Vos uses a VHF antenna to locate cheetahs in Phinda Game Reserve. Tony Carnie for Mongabay
Swinging for the Fences<p>But other wildlife conservation leaders have a different perspective on cheetah conservation strategy.</p><p>Gus Mills, a senior carnivore researcher retired in 2006 from SANParks, the agency that manages South Africa's national parks, after a career of more than 30 years in Kalahari and Kruger national parks. He says the focus should be on quality of living spaces rather than the quantity of cheetahs.</p><p>Mills, who was the founder of the Endangered Wildlife Trust's Carnivore Conservation Group in 1995, and who also spent six years after retirement studying cheetahs in the Kalahari, says it's more important to properly protect and, where possible, expand the size of existing protected areas.</p><p>He also advocates a triage approach to cheetah conservation, in which scarce funds and resources are focused on protecting cheetahs in formally protected areas, rather than diluting scarce resources in an attempt to try and save every single remaining cheetah population.</p><p>"People have an obsession with numbers. But I believe that it is more important to protect large landscape and habitats properly," Mills said.</p><p>He suggests that cheetahs enclosed within small reserves live in artificial conditions: "It's almost like glorified farming."</p><p>"In the long run we have to focus on consolidating formally protected areas," he added. "Africa's human population will double by 2050, so cheetah populations in unfenced areas will become unsustainable if they are eating people's livestock."</p>
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