
By Daisy Dunne
Spraying aerosols high in the stratosphere could dampen global warming over land, but may not prevent the oceans from heating up, new research says.
The findings suggest that this type of "solar geoengineering"—a set of techniques that aim to tackle global warming by reflecting sunlight back into space—may not necessarily stem sea level rise or prevent damage to the world's marine ecosystems.
The research indicates that solar geoengineering could carry "major uncertainties and risks," the lead author told Carbon Brief.
The study also raises the issue of whether global average temperature "is the best metric to control" when addressing the impacts of climate change, another scientist told Carbon Brief.
Harnessing a Volcano
Scientists have suggested that releasing aerosols into the atmosphere—a technique known as "stratospheric aerosol injection"—could cool the planet in a similar way to a large volcanic eruption.
When a volcano erupts, it sends an ash cloud high into the atmosphere. The sulphur dioxide released in the plume combines with water to form sulfuric acid aerosols, which reflect away incoming sunlight, temporarily cooling the Earth.
Artificially introducing aerosols into the atmosphere—via a plane or a high-altitude balloon—could have a similar cooling effect, researchers say.
The idea has never been tested, but previous research using computer simulations suggests that releasing aerosols could help limit global temperature rise to 1.5C—the aspirational target of the Paris agreement—and keep rainfall from becoming irregular.
However, an aerosol sunshade would not protect the planet from rising CO2 emissions—which is causing oceans to become more acidic and crops to become less nutritious, among other problems.
The new study, published in Nature Geoscience, identifies, for the first time, another potential downfall of the proposed technique: it may not be able to limit warming in the deep ocean.
This is because aerosol release could cause rainfall to decrease in some regions, which could influence ocean circulation patterns, says lead author Dr. John Fasullo, a project scientist at the National Center for Atmospheric Research (NCAR), Boulder. He told Carbon Brief:
"The explanation involves two key stages. In the first, the aerosols reduce the amount of rainfall that occurs globally. This change in rainfall is not uniform, rather, reductions are larger in some key regions—namely, the northern Atlantic Ocean—and this increases the salinity of those ocean areas, making the water more dense."
This increase in water density could cause the "Atlantic Meridional Overturning Circulation" (AMOC) to speed up, he said. The AMOC is a perpetual conveyor belt that transports heat from the equator up to the North Atlantic. It is part of a wider network of global ocean circulations patterns that transports heat all around the world. Fasullo said:
"The North Atlantic is a key region of deep-water formation and higher density therefore leads to an acceleration of this circulation. The speed up in deep-water formation buries more heat in the deep ocean that would have otherwise occurred."
Other Worlds
To explore the impact of aerosol release on oceans, the researchers used a set of 20 computer simulations looking at what would happen if aerosols were released between 2020 and 2099. This set of simulations is known as the "geoengineering large ensemble" (GLENS).
The simulations assume that aerosols are released at uniform points across the globe. (Previous research shows doing this would prevent large regional changes in temperature and weather.)
The researchers compared their geoengineering simulations to another set of simulations where no geoengineering takes place and little action is taken to tackle climate change, leading to high emissions in the coming decades (a scenario known as "RCP8.5").
The chart below shows how global average temperature (full lines, left-hand y-axis) and global rainfall levels (dashed lines, right-hand y-axis) are expected to differ between the high-emissions scenario (RCP8.5) simulations and GLENS.
Above: Changes to global mean temperature (full lines, left-hand y-axis) and global rainfall levels (dashed lines, right-hand y-axis) under a scenario with solar geoengineering (GLENS; blue) and a scenario with no geoengineering and high greenhouse gas emissions (RCP8.5; red). Source: Fasullo et al. (2018)
The chart shows how, in the geoengineered world, the global average temperature is kept constant while global rainfall levels fall. In comparison, temperatures and rainfall levels continue to rise under the high-emissions scenario.
The maps below show expected changes to ocean heat content (OHC) between 2010-30 and 2075-95 in the upper ocean (0-300m; left) and in the full-depth of the ocean (right) under the geoengineering scenario. On the maps, red shows increases in OHC, while blue shows decreases.
Above: Expected changes to ocean heat content (OHC) between 2010-30 and 2075-95 in the upper ocean (0-300m; left) and in the full-depth of the ocean (right) under a solar geoengineering scenario. Red shows increases in OCH, while blue shows decreases. Source: Fasullo et al. (2018)
The charts show how, in the geoengineering scenario, some shallower parts of the ocean are expected to heat up. This includes the Arctic Sea and waters off the western coast of North America.
When the full depth of the ocean is considered, however, many more regions are expected to see OHC increases—with warming likely to be most severe in the Arctic Sea and in the Southern Ocean.
Rising Tides
The findings suggest that—contrary to previous research—solar geoengineering could fail to prevent sea level rise.
Sea level rise is chiefly driven by the expansion of seawater as a result of warming and by the melting of land ice at the world's poles. In some parts, including in Western Antarctica, melting occurs where land ice comes into contact with warm ocean water. Fasullo said:
"Relative to present day, it is extremely likely that sea level will continue to rise under our geoengineering approach, but it is also likely that the rate of this rise will be less than under a business-as-usual climate trajectory [RCP8.5].
"We cannot say with confidence what that rate of rise might be as we don't have models of the ice sheets fully coupled to our climate simulations, nor have we sufficiently vetted such models to have confidence in their projections at this point."
The results could also mean that solar geoengineering would fail to prevent marine heatwaves, which pose a major threat to undersea wildlife, and the expected increases in hurricane intensity. (Although no research has looked at these issues, specifically, so it is still too soon to draw conclusions, Fasullo said.)
The study raises the issue of whether global average temperature "is the best metric to control" when addressing the impacts of climate change, said Prof. Govindasamy Bala, a physical scientist from the Divecha Centre for Climate Change at the Indian Institute of Science, who was not involved in the study. He told Carbon Brief:
"However, as this is a single modeling study, it is not clear to me if the results of this paper are robust. A multi-model based approach would be needed to verify the robustness."
The findings imply that solar geoengineering could have "large potential downsides," said Fasullo:
"There have been various high-profile policymakers in the U.S. that have framed climate change as an engineering challenge. I think the key takeaway from our work is that geoengineering itself carries major uncertainties and risks."
Reposted with permission from our media associate Carbon Brief.
‘Existential Threat to Our Survival’: See the 19 Australian Ecosystems Already Collapsing
By Dana M Bergstrom, Euan Ritchie, Lesley Hughes and Michael Depledge
In 1992, 1,700 scientists warned that human beings and the natural world were "on a collision course." Seventeen years later, scientists described planetary boundaries within which humans and other life could have a "safe space to operate." These are environmental thresholds, such as the amount of carbon dioxide in the atmosphere and changes in land use.
The Good and Bad News
<p><span>Ecosystems consist of living and non-living components, and their interactions. They work like a super-complex engine: when some components are removed or stop working, knock-on consequences can lead to system failure.</span></p><p>Our study is based on measured data and observations, not modeling or predictions for the future. Encouragingly, not all ecosystems we examined have collapsed across their entire range. We still have, for instance, some intact reefs on the Great Barrier Reef, especially in deeper waters. And northern Australia has some of the most intact and least-modified stretches of savanna woodlands on Earth.</p><p><span>Still, collapses are happening, including in regions critical for growing food. This includes the </span><a href="https://www.mdba.gov.au/importance-murray-darling-basin/where-basin" target="_blank" rel="noopener noreferrer">Murray-Darling Basin</a><span>, which covers around 14% of Australia's landmass. Its rivers and other freshwater systems support more than </span><a href="https://www.abs.gov.au/ausstats/[email protected]/latestproducts/94F2007584736094CA2574A50014B1B6?opendocument" target="_blank" rel="noopener noreferrer">30% of Australia's food</a><span> production.</span></p><p><span></span><span>The effects of floods, fires, heatwaves and storms do not stop at farm gates; they're felt equally in agricultural areas and natural ecosystems. We shouldn't forget how towns ran out of </span><a href="https://www.mdba.gov.au/issues-murray-darling-basin/drought#effects" target="_blank" rel="noopener noreferrer">drinking water</a><span> during the recent drought.</span></p><p><span></span><span>Drinking water is also at risk when ecosystems collapse in our water catchments. In Victoria, for example, the degradation of giant </span><a href="https://theconversation.com/logging-must-stop-in-melbournes-biggest-water-supply-catchment-106922" target="_blank" rel="noopener noreferrer">Mountain Ash forests</a><span> greatly reduces the amount of water flowing through the Thompson catchment, threatening nearly five million people's drinking water in Melbourne.</span></p><p>This is a dire <em data-redactor-tag="em">wake-up</em> call — not just a <em data-redactor-tag="em">warning</em>. Put bluntly, current changes across the continent, and their potential outcomes, pose an existential threat to our survival, and other life we share environments with.</p><p><span>In investigating patterns of collapse, we found most ecosystems experience multiple, concurrent pressures from both global climate change and regional human impacts (such as land clearing). Pressures are often </span><a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2664.13427" target="_blank" rel="noopener noreferrer">additive and extreme</a><span>.</span></p><p>Take the last 11 years in Western Australia as an example.</p><p>In the summer of 2010 and 2011, a <a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637" target="_blank" rel="noopener noreferrer">heatwave</a> spanning more than 300,000 square kilometers ravaged both marine and land ecosystems. The extreme heat devastated forests and woodlands, kelp forests, seagrass meadows and coral reefs. This catastrophe was followed by two cyclones.</p><p>A record-breaking, marine heatwave in late 2019 dealt a further blow. And another marine heatwave is predicted for <a href="https://www.theguardian.com/environment/2020/dec/24/wa-coastline-facing-marine-heatwave-in-early-2021-csiro-predicts" target="_blank" rel="noopener noreferrer">this April</a>.</p>What to Do About It?
<p><span>Our brains trust comprises 38 experts from 21 universities, CSIRO and the federal Department of Agriculture Water and Environment. Beyond quantifying and reporting more doom and gloom, we asked the question: what can be done?</span></p><p>We devised a simple but tractable scheme called the 3As:</p><ul><li>Awareness of what is important</li><li>Anticipation of what is coming down the line</li><li>Action to stop the pressures or deal with impacts.</li></ul><p>In our paper, we identify positive actions to help protect or restore ecosystems. Many are already happening. In some cases, ecosystems might be better left to recover by themselves, such as coral after a cyclone.</p><p>In other cases, active human intervention will be required – for example, placing artificial nesting boxes for Carnaby's black cockatoos in areas where old trees have been <a href="https://www.environment.gov.au/biodiversity/threatened/publications/factsheet-carnabys-black-cockatoo-calyptorhynchus-latirostris" target="_blank" rel="noopener noreferrer">removed</a>.</p><p><span>"Future-ready" actions are also vital. This includes reinstating </span><a href="https://www.abc.net.au/gardening/factsheets/a-burning-question-fire/12395700" target="_blank" rel="noopener noreferrer">cultural burning practices</a><span>, which have </span><a href="https://theconversation.com/australia-you-have-unfinished-business-its-time-to-let-our-fire-people-care-for-this-land-135196" target="_blank" rel="noopener noreferrer">multiple values and benefits for Aboriginal communities</a><span> and can help minimize the risk and strength of bushfires.</span></p><p>It might also include replanting banks along the Murray River with species better suited to <a href="https://www.abc.net.au/gardening/factsheets/my-garden-path---matt-hansen/12322978" target="_blank" rel="noopener noreferrer">warmer conditions</a>.</p><p>Some actions may be small and localized, but have substantial positive benefits.</p><p>For example, billions of migrating Bogong moths, the main summer food for critically endangered mountain pygmy possums, have not arrived in their typical numbers in Australian alpine regions in recent years. This was further exacerbated by the <a href="https://theconversation.com/six-million-hectares-of-threatened-species-habitat-up-in-smoke-129438" target="_blank" rel="noopener noreferrer">2019-20</a> fires. Brilliantly, <a href="https://www.zoo.org.au/" target="_blank" rel="noopener noreferrer">Zoos Victoria</a> anticipated this pressure and developed supplementary food — <a href="https://theconversation.com/looks-like-an-anzac-biscuit-tastes-like-a-protein-bar-bogong-bikkies-help-mountain-pygmy-possums-after-fire-131045" target="_blank" rel="noopener noreferrer">Bogong bikkies</a>.</p><p><span>Other more challenging, global or large-scale actions must address the </span><a href="https://www.youtube.com/watch?v=iICpI9H0GkU&t=34s" target="_blank" rel="noopener noreferrer">root cause of environmental threats</a><span>, such as </span><a href="https://www.nature.com/articles/s41559-018-0504-8" target="_blank" rel="noopener noreferrer">human population growth and per-capita consumption</a><span> of environmental resources.</span><br></p><p>We must rapidly reduce greenhouse gas emissions to net-zero, remove or suppress invasive species such as <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12080" target="_blank" rel="noopener noreferrer">feral cats</a> and <a href="https://theconversation.com/the-buffel-kerfuffle-how-one-species-quietly-destroys-native-wildlife-and-cultural-sites-in-arid-australia-149456" target="_blank" rel="noopener noreferrer">buffel grass</a>, and stop widespread <a href="https://theconversation.com/to-reduce-fire-risk-and-meet-climate-targets-over-300-scientists-call-for-stronger-land-clearing-laws-113172" target="_blank" rel="noopener noreferrer">land clearing</a> and other forms of habitat destruction.</p>Our Lives Depend On It
<p>The multiple ecosystem collapses we have documented in Australia are a harbinger for <a href="https://www.iucn.org/news/protected-areas/202102/natures-future-our-future-world-speaks" target="_blank">environments globally</a>.</p><p>The simplicity of the 3As is to show people <em>can</em> do something positive, either at the local level of a landcare group, or at the level of government departments and conservation agencies.</p><p>Our lives and those of our <a href="https://theconversation.com/children-are-our-future-and-the-planets-heres-how-you-can-teach-them-to-take-care-of-it-113759" target="_blank">children</a>, as well as our <a href="https://theconversation.com/taking-care-of-business-the-private-sector-is-waking-up-to-natures-value-153786" target="_blank" rel="noopener noreferrer">economies</a>, societies and <a href="https://theconversation.com/to-address-the-ecological-crisis-aboriginal-peoples-must-be-restored-as-custodians-of-country-108594" target="_blank" rel="noopener noreferrer">cultures</a>, depend on it.</p><p>We simply cannot afford any further delay.</p><p><em><a rel="noopener noreferrer" href="https://theconversation.com/profiles/dana-m-bergstrom-1008495" target="_blank" style="">Dana M Bergstrom</a> is a principal research scientist at the University of Wollongong. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/euan-ritchie-735" target="_blank" style="">Euan Ritchie</a> is a professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences at Deakin University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/lesley-hughes-5823" target="_blank">Lesley Hughes</a> is a professor at the Department of Biological Sciences at Macquarie University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/michael-depledge-114659" target="_blank">Michael Depledge</a> is a professor and chair, Environment and Human Health, at the University of Exeter. </em></p><p><em>Disclosure statements: Dana Bergstrom works for the Australian Antarctic Division and is a Visiting Fellow at the University of Wollongong. Her research including fieldwork on Macquarie Island and in Antarctica was supported by the Australian Antarctic Division.</em></p><p><em>Euan Ritchie receives funding from the Australian Research Council, The Australia and Pacific Science Foundation, Australian Geographic, Parks Victoria, Department of Environment, Land, Water and Planning, and the Bushfire and Natural Hazards CRC. Euan Ritchie is a Director (Media Working Group) of the Ecological Society of Australia, and a member of the Australian Mammal Society.</em></p><p><em>Lesley Hughes receives funding from the Australian Research Council. She is a Councillor with the Climate Council of Australia, a member of the Wentworth Group of Concerned Scientists and a Director of WWF-Australia.</em></p><p><em>Michael Depledge does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</em></p><p><em>Reposted with permission from <a href="https://theconversation.com/existential-threat-to-our-survival-see-the-19-australian-ecosystems-already-collapsing-154077" target="_blank" style="">The Conversation</a>. </em></p>- Coral Reef Tipping Point: 'Near-Annual' Bleaching May Occur ... ›
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