New Study ‘Reduces Uncertainty’ for Climate Sensitivity
By Daisy Dunne
The new study, published in Nature, refines this estimate to 2.8°C, with a corresponding range of 2.2 to 3.4°C. If correct, the new estimates could reduce the uncertainty surrounding climate sensitivity by 60 percent.
The narrower range suggests that global temperature rise is "going to shoot over 1.5°C" above pre-industrial levels, the lead author told Carbon Brief, but "we might be able to avoid 2°C." Meeting either limit will likely require negative emissions technologies that can remove CO2 from the atmosphere, he said.
The new estimate is another "brick in the wall" of scientists' understanding of climate sensitivity, another scientist told Carbon Brief, and "the best-informed views will be reached by multiple lines of evidence."
Climate sensitivity is the amount of warming that can be expected in response to the concentration of CO2 in the atmosphere reaching double the level observed in pre-industrial times.
The research makes a new estimate of the "equilibrium" climate sensitivity (ECS)—that is, the amount of warming expected to occur once the full impact of the extra greenhouse gases release has played out. This measure includes the impact of warming on long-term climate feedback loops, which can take decades, or even centuries, to materialize.
The value of ECS is one of the big climate change questions that scientists are still trying to address.
It is important because understanding how sensitive the Earth is to CO2 could help us to estimate how much the planet could warm in response to greenhouse gases, explained professor Peter Cox, lead author of the new paper and a climate scientist at the University of Exeter. He told Carbon Brief:
"The issue about the equilibrium climate sensitivity is the range that has been given in successive IPCC reports – 1.5 to 4°C—is a range that is essentially 'climate change we could probably adapt to' at the 1.5°C end and 'climate change we probably can't adapt to' at the 4°C end. So that uncertainty has a huge impact on impeding the focused effort to mitigate climate change and adapt."
The new findings indicate that the value of ECS could be close to 2.8°C, said Cox:
"We get a value with a 'likely' range, which means there's a 66 percent probability that it's in that range of 2.2 to 3.4°C with a central estimate of 2.8°C. That's not so far from the central estimate of the IPCC which is 3°C, but the range is much reduced, from 1.5 to 4°C, to 2.2 to 3.4°C. What that means is we can rule out very low climate sensitivities and we can rule out very high climate sensitivities."
Capturing a Signal
There are a number of techniques that scientists can use to work out what ECS could be.
One method is to look at how Earth has responded to natural greenhouse gas changes in its geological past to try to work out how it might respond to future global warming.
A third method used by scientists involves matching global surface temperatures with the global warming trend over the past century to try and work out sensitivity from how the planet is responding. (This is what is known as the "energy budget model" approach.)
The new study uses a similar method to the energy budget model approach. However, instead of matching the global temperature record to global warming, the new research attempts to match temperature records to natural, long-term fluctuations in temperature.
Looking at natural variability rather than the warming trend allowed the scientists to exclude a range of uncertainties associated with human-caused climate change, Cox explained:
"Normally the way this [research] is done is by looking at the historical record warming, which makes sense. We've seen 1°C of warming, roughly speaking, and so you may think that must tell you how sensitive the climate is. But it doesn't. The main reason it doesn't is that we don't know how much energy or heat we've put in the system in terms of radiative forcing—greenhouse gases."
To understand how historical temperature fluctuations have changed over the past century, the researchers first removed the global warming trend from a set of observational temperature data.
They then compared this data to results from a series of 22 global climate models. Some models had lower climate sensitivity, while some some models had higher climate sensitivity.
The results are shown on the chart below. On the chart, black dots show natural fluctuations in temperature from 1940 to 2020. Each line represents the results from one model, with magenta lines showing results from higher sensitivity models and green showing the results from models with lower climate sensitivity.
Natural temperature variability (black dots) compared to simulations of variability from climate models with higher climate sensitivity (magenta) and lower climate sensitivity (green). Each line represents the results from one model.Cox et al. (2018)
The chart indicates that higher sensitivity models generally predict a higher level of variability than has been observed over the past 50 years, while lower sensitivity models either closely match the observed trend or estimate a lower amount of variability.
Together, these results allowed the researchers to produce their narrower range.
Understanding ECS could help scientists to work out how much the climate is likely to warm in the future, Cox said, which in turn could allow policymakers to estimate how easy it will be to meet the goals of the Paris agreement.
Climate sensitivity is the amount of warming that will occur after CO2 concentrations become twice as high as they were in pre-industrial times. Pre-industrial CO2 concentration levels were about 280 parts per million (ppm) and levels are currently at around 404 ppm.
This means that, if humans stopped releasing CO2 today, the world should expect to experience more than half of the warming dictated by the ECS. Cox explained:
"That means that if you've got an ECS of 4°C, then you've pretty much already missed the 2°C target of Paris. So the ECS value has a big impact on the feasibility of Paris."
If the results are correct and the climate sensitivity is 2.8°C, then it is likely that the world will fail to limit warming to 1.5°C above pre-industrial levels, which is the aspirational goal of the Paris agreement, Cox added:
"Our numbers suggest that we're going to shoot over 1.5°C. We might be able to avoid 2°C—it will take a huge effort to do so. I think, to achieve 1.5°C, you definitely have to think of negative emissions technologies and, if you want 2°C, you need to think about it, too, even if it's only a short-term stop gap."
Negative emissions technologies are a group of techniques—many of which still remain hypothetical—that aim to remove CO2 from the air in an attempt to tackle climate change.
The study's results "reduce the probability of very high climate sensitivity," which should "reassure" those taking steps to meet the goals of the Paris agreement, said professor Gabi Hegerl, a climate system scientist from the University of Edinburgh, who was not involved in the research. She told Carbon Brief:
"It also emphasizes that climate change won't be small, so reducing climate change will continue to require very sharp reductions of emissions leading towards ceasing emissions."
Reducing uncertainty surrounding climate sensitivity should help policymakers to refocus their efforts on tackling climate change, said Cox:
"If you can reduce the uncertainty, which I think we can, then you can focus your mind on what needs to be done. We can rule out very low values, where you might say, 'don't worry about it, we'll adapt' and you can rule out very high values that might lead to you to a sort of hopeless[ness] where you think, 'it's too late.' We are still in that zone where action is urgent, but not too late. But it is very urgent."
'Brick in the Wall'
The new paper adds to the extensive research around the potential value for ECS.
Despite debate among scientists about the best way to estimate climate sensitivity, each new research paper can be seen as a "brick in the wall" of our understanding, said professor Andrew Dessler, an atmospheric scientist from Texas A&M University, who was not involved in the research. He told Carbon Brief:
"I don't think any single paper will by itself redefine what we think about ECS. Rather, the best-informed views will be reached by multiple lines of evidence, with care taken in relating the inferred ECS from different methods."
The methods used in the study are "credible," said professor Steven Sherwood, deputy director of the Climate Change Research Centre at the University of New South Wales. However, it does have its limitations, he said.
For example, the paper does not discuss how natural events, such as El Niño, could impact temperature fluctuations, he told Carbon Brief:
"The approach mixes up natural variability due to El Niño, decadal variations, volcanic eruptions and air pollutants, and we know that models have different biases with respect to each of these. There are also theoretical problems with applying their statistical approach in this way, even though it seems to work. So it is not clear whether to put more weight on this study, or the previous ones suggesting even higher sensitivity."
In addition, the research may have made "significant" errors in its attempts to reduce uncertainty surrounding climate sensitivity, said Dr. Patrick Brown, a climate scientist from the Carnegie Institution for Science in Stanford, California.
Last month, Brown was the lead author of a Nature paper which found that ECS could be relatively higher than previous estimates have suggested—their central estimate was 3.7°C. Brown told Carbon Brief:
"They appear to be comparing the IPCC ECS 'likely' range of 1.5 to 4.5°C to their constrained ECS model range. This is not an appropriate comparison because the 16 models that they use do not span the entire uncertainty range of ECS.
"For example, no model that they investigate has an ECS below 2.2°C. Thus their claim that they reduced uncertainty in ECS by 60 percent comes partly from the coincidence of which models happened to be included in their study."
However, writing in an accompanying News & Views article, professor Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds, who was also not involved in the research, argues that some published estimates for ECS have "depended on the researchers' assumptions about ECS, rather than the evidence." He wrote:
"By contrast, Cox et al started from climate-model values that are at the upper end of the IPCC range and used evidence to effectively rule out catastrophically high values."
Forster added that the methods used in the present study are "enviably simple" and will leave climate scientists asking, "why didn't I think of that?" He said:
"In my view, Cox and colleagues' estimate and the estimates produced by analysing the historical energy budget carry the most weight, because they are based on simpler physical theories of climate forcing and response, and do not directly require the use of a climate that correctly represents cloud."
Reposted with permission from our media associate Carbon Brief.
EcoWatch Daily Newsletter
By Zahida Sherman
Cooking has always intimidated me. As a child, I would anxiously peer into the kitchen as my mother prepared Christmas dinner for our family.
Falling in Love With Food All Over Again<p>Slowly, through my most intimate relationships with friends and partners, I began to see the beauty — and rewards — of cooking.</p><p>I got tired of giving in to defeat and always bringing chips or paper products to social gatherings. I started asking my mom to send me her Christmas and Thanksgiving recipes. I even volunteered to host Thanksgiving dinner at my place.</p><p>Each time I heard my loved ones sing the praises of the foods I prepared for them, I felt a tinge more confident that I could carry out our traditions my way.</p><p>In reaching out to other relatives for their favorite recipes, I learned that they had a little help of their own. They didn't rely solely on their ancestral cooking instincts. They turned to Black chefs for guidance.</p><p>These 7 cookbooks by Black chefs have inspired my family and fed us in nutrients, joy, and spiritual sustenance. They're also helping me overcome my personal fears of cooking.</p>
Get CookingWhether you're in recovery from cooking fears like me, or are just looking to expand your culinary confidence with dishes honoring Black heritage, these Black chefs are here to support you on your journey.Turn on some music, give yourself permission to make mistakes, and throw down for yourself or your loved ones. Glorious flavors await you.
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By Tara Lohan
The conclusion to decades of work to remove a dam on the Middle Fork Nooksack River east of Bellingham, Washington began with a bang yesterday as crews breached the dam with a carefully planned detonation. This explosive denouement is also a beginning.
The History<p>The Middle Fork Nooksack drains glacier-fed headwater streams that run off the icy summit of 10,778-foot Mt. Baker. The Middle Fork joins the North Fork and then the mainstem of the Nooksack River, which travels to Bellingham Bay and Puget Sound. The entire Nooksack watershed stretches 830 square miles across Washington and into British Columbia.</p>
A Plan Comes Together<p>The Middle Fork dam is not a pool dam built for water storage. Much of the time, water flows over the top until dam operators drop a floodgate to divert water to new locations. That water travels about 14 miles through tunnel and pipeline to Mirror Lake, then Anderson Creek, and to Lake Whatcom before finally being delivered to residents' taps.</p><p>Before removing the dam, engineers had to move the water intake 700 feet upstream and situate it at an elevation that still enabled city water withdrawals throughout the year, regardless of flow conditions.</p><p>They also needed to make sure that the rushing water didn't sweep up fish and accidentally send them through the water-supply system.</p><p>"The solution required a fairly complex design in the intake structure, including a fish exit pipe out of that structure to put fish back into the river in a way that meets current environmental permit standards," explains LaCroix.</p>
Project layout for the removal of the Middle Fork Nooksack diversion dam and rebuilding of water intake. City of Bellingham<p>Despite the cost and the work, she says, being able to continue to meet their municipal water obligations while opening up habitat for threatened species has been a win-win.</p><p>"I think there's a lot of benefits to having a dam removal versus fish passage — the main one being that you get a free-flowing river that can be a dynamic ecosystem and change over time," she says. "A static fish ladder just can't provide that same level of ecosystem benefit."</p>
Restoration Success<p>Despite local authorities' championing dam removal on the Middle Fork, the project has largely flown under the radar, overshadowed in the Pacific Northwest by heated discussions about a much larger potential project — removing <a href="https://www.seattletimes.com/seattle-news/feds-reject-removal-of-4-snake-river-dams-in-key-report/" target="_blank">four federal hydroelectric dams on the lower Snake River</a>, a major tributary of the Columbia River.</p><p>Proponents of dam removal there see it as the best chance for recovering threatened salmon populations, including Chinook, which could help starving Southern Resident killer whales. Those dams also provide irrigation water, barge navigation and hydropower, so there's been more pushback against removal efforts.</p><p>Previous dam removals around the country, however, have proved successful at aiding fish recovery and river restoration.</p><p>Most notably the 1999 demolition of <a href="https://therevelator.org/edwards-dam-removal/" target="_blank">Edwards Dam on Maine's Kennebec River</a> restored the annual run of alewives, a type of herring essential to the food web. The fish run has gone from zero to 5 million in the two decades since dam removal. Blueback herring, striped bass, sturgeon and shad have also extended their reach. And the resurgence has brought back osprey, bald eagles and other wildlife, too.</p><p>The overwhelming success of river restoration on the Kennebec helped to spur a nationwide dam removal movement that's now seen 1,200 dams come down since 1999. Last year a record <a href="https://www.americanrivers.org/conservation-resource/a-record-26-states-removed-dams-in-2019/" target="_blank">90 dams</a> were removed in 26 states, including <a href="https://therevelator.org/cleveland-forest-dam-removal/" target="_blank">20 dams in California's Cleveland National Forest</a>.</p>
Spider excavators remove on dam on San Juan Creek in California's Cleveland National Forest. Julie Donnell, USFS<p>The results have been seen in the Pacific Northwest, as well, which boasts the largest dam removal thus far in the country. In 2011 and 2014, the demolition of <a href="https://therevelator.org/elwha-dam-removal/" target="_blank">two dams</a> on Elwha River, which runs through Washington's Olympic National Park, opened up 70 miles of habitat that had been blocked for a century. Scientists have started seeing all five species of salmon native to the river coming back, particularly Chinook and coho. Bull trout, they've observed, have increased in size since the dams were removal.</p>
Benefits on the Middle Fork Nooksack<p>McEwan hopes to see a similar outcome on the Middle Fork.</p><p>Like the Elwha the Middle Fork Nooksack is a relatively pristine river with little development, and dam removal is expected to provide a big boost to fish. The additional miles of spawning habitat are important, but so is the temperature of that water.</p><p>The dam removal will open access to cold upstream waters, which are ideal for salmon and getting harder to come by as climate change warms waters and reduces mountain runoff.</p><p>"This is really great for the climate change resiliency for these species," says McEwan.</p><p>Steelhead will get back 45% of their historic habitat in the river, and scientists expect Chinook populations to increase in abundance by 31%.</p><p>That <em>could</em> help Southern Resident killer whales.</p><p>"When you get to the ocean, it's a little bit of a black box in terms of what you can model and say definitively is going to help, but more fish is better for orcas," McEwan says.</p><p>Upstream habitat will see benefits, too.</p><p>Oceangoing fish like salmon enrich their bodies with carbon and nitrogen while at sea. When they return to their natal rivers to spawn and die, the marine-derived nutrients they carry back upriver become important food and fertilizer for both riverine and terrestrial ecosystems — aiding everything from trees to birds to bears.</p><p>"Once the fish start making their way back, it will start changing the whole ecological system," says Delgado.</p><p><span></span>But any ecological benefit from salmon restoration, either in the ocean or the upper watershed, won't be immediate.<br></p><p>"The population of salmon on the Middle Fork is so low that we expect it's going to take quite a while to rebound," she says. "But the big picture is that what's good for salmon is good for the region — our history and our destiny are intricately intertwined."</p><p>After decades of work, that process of restoration has finally begun.</p>
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By Katie Howell
A new tool called The Food Systems Dashboard aims to save decision makers time and energy by painting a complete picture of a country's food system. Created by the Johns Hopkins' Alliance for a Healthier World, the Global Alliance for Improved Nutrition (GAIN), and the U.N. Food and Agriculture Organization (FAO), the Dashboard compiles food systems data from over 35 sources and offers it as a public good.
By Manuela Callari
It can grow to a maximum of six inches (16 centimeters), change color depending on mood and habitat, and, like all seahorses, the White's seahorse male gestates its young. But this tiny snouted fish is under threat.
Building an Ocean Seahorse Destination<p>Seahorses are found in tropical and temperate coastal water worldwide, but are most abundant around Australia, China and the Philippines. </p><p>Trade in the tiny creatures is strictly regulated because of their use in traditional medicine, aquariums and their sale as dried curios. But because they are poor swimmers and cannot easily move elsewhere, habitat loss is a particular threat for these curious animals. </p><p>Seahorses wrap their tails around seagrass and corals to avoid being carried away on currents. They use the habitat to spawn and hide from predators such as crabs, while also feeding on riches of plankton and small crustaceans living in the reef.</p><p><span></span>Where corals aren't available, <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/aqc.1217" target="_blank">scientists</a> found seahorses taking up residence in fishing nets and old crab traps abandoned at the bottom of the ocean. </p>
Mixing With the Locals<p>Baby seahorse mortality is high in the wild because they are easily caught, so those bred in the protected environment of the aquarium weren't ready to be released into the wild until early May.</p><p>The team released 90 new arrivals into Sydney Harbor, placing some directly into the purpose-built hotels, and others onto a net that wild seahorses had already settled on.</p><p>Before setting them free, the researchers marked each young seahorse with a fluorescent tag with unique IDs inserted just beneath the skin to track how they get on in the different environments. </p><p>"The most exciting part was being able to put these animals into the wild and then go back a month later and still see them surviving and growing," said McCracken. </p><p>The seahorses will be old enough to mate and reproduce around October or November 2020. And researchers hope that by then, they will be able to breed with the wild population. </p>
Building a Global Seahorse Hotel Chain<p>With seahorses everywhere facing the loss of their coral reef homes, similar projects have sprung up in places like Greece and South Africa, home to the world's most endangered seahorse, the Knysna seahorse. </p><p>"The endangered South African seahorse is benefiting from something quite similar, even though it wasn't intentional," said Peter Teske, professor at the Department of Zoology, University of Johannesburg.</p><p>In the South African <a href="https://www.researchgate.net/publication/322649251_An_endangered_seahorse_selectively_chooses_an_artificial_structure" target="_blank">case</a>, seahorses have bedded down in "Reno mattresses" — wire cages filled with rocks — that were used to build a new marina. Researchers from NGO Knysna Basin Project found the structures acted as a refuge for the animals.<span></span></p><p><span></span>While Teske describes the seahorse hotels as "a positive news story" and a great way to create public awareness of conservation, he added that establishing artificial habitats in some areas will only prevent the extinction of local populations.</p><p>"For a complete recovery, it is necessary to give the natural habitat a chance to regenerate," said the seahorse expert. </p>
Underwater Mascot<p>In Australia, the researchers hope the project could provide an opportunity to raise awareness not only of the plight of the Sydney seahorses but the other animals with which it shares its ocean habitat.</p><p>The waters around Sydney and the east coast are rich in biodiversity and include several threatened species like the weedy seadragon — a relative of the seahorse — and the grey nurse shark. Like the seahorse, they're also under pressure from pollution, ocean traffic and habitat loss through storms and coastal construction. </p><p>"It's a good thing to get people's support and interest. The seahorses are a useful vehicle to get people concerned if the harbor is in trouble," said David Booth, professor of marine ecology at the University of Technology Sydney who is also working on the project. </p><p>The hotels have become an attraction for divers hoping to catch a glimpse of these small but near mythical creatures. </p><p>"Everyone loves seahorses," added Booth, "they are so popular." </p>
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