Climate Change to Become ‘Greatest Pressure on Biodiversity’ by 2070
By Daisy Dunne
The combined effects of global warming and land-use change could cause the world's ecosystems to lose more than a third of their animal species by 2070, a new study finds.
The local loss of species could greatly impair the ability of ecosystems to function as normal, the lead author told Carbon Brief, which could, in turn, threaten natural services, such as pollination.
However, restricting global warming to 2C above pre-industrial levels—which is the limit of the Paris agreement—could reduce the risk facing the world's ecosystems, the author adds.
Rising temperatures and changing rainfall patterns are expected to make existing habitats inhospitable for many animal species. Biodiversity is also under threat from land-use change caused by agriculture, deforestation and land degradation.
The new study, published in Proceedings of the Royal Society of London B, considers how both of these threats could combine to affect ecosystems across the world in the coming decades.
The research finds that, in a future with relatively high amounts of global warming and land-use change, the number of animal species in the average ecosystem could fall by 38 percent, when compared to conditions from 1961-90.
However, some ecosystems are expected to face larger species losses than others, said study author Dr. Tim Newbold, a research fellow at the Centre for Biodiversity and Environment Research at University College London. He told Carbon Brief:
"Climate change is to become, perhaps, the greatest pressure on biodiversity and overtake land-use in terms of impacts on biodiversity. If you combine these things together, the predictions are—at least under business as usual—for very large losses of biodiversity."
For his research, Newbold used modelling to produce a set of maps showing the expected impact of global warming and land-use change—and where these threats could overlap—in different parts of the world.
His results were based on four possible future scenarios, known as the "Representative Concentration Pathways" (RCPs). Each scenario makes assumptions about a range of parameters, including the future rate of greenhouse gas release, the efforts made to combat climate change (mitigation) and the rate of global population growth.
The scenarios include: an "optimistic" scenario which assumes global warming is restricted to below 2C (RCP2.6); a scenario where warming reaches 2-3C (RCP4.5); a scenario where warming reaches 2.6-3.7C (RCP6.0); and a "business-as-usual" scenario where warming reaches 4-6C (RCP8.5). (Carbon Brief has previously described these four RCPs in more detail.)
The maps below show where losses are expected to be "high" (greater than 10 percent of species lost) as a result of climate change (orange) and land-use change (blue) for each scenario. Areas where high losses from global warming and land-use change overlap are also shown (black), as well as where species loss is expected to be low (grey).
Expected biodiversity loss from climate and land-use change by 2070 under (top left to bottom right) RCP2.6, RCP4.5, RCP6.0 and RCP8.5. The maps include where losses are expected to be "high" (greater than 10% of species lost) as a result of climate change (orange) and land-use change (blue) for each scenario. Areas where high losses from global warming and land-use change overlap are also shown (black), as well as where species loss is expected to be low (grey).
The charts show that the combined impacts of climate change and land-use are expected to be highest under the "business-as-usual" scenario. In this scenario, land-use change is expected to cause biodiversity losses of 2 percent, while global warming is expected to cause losses of 29 percent.
Biodiversity losses are expected to be particularly high in the tropical grasslands and savannahs of southern Africa and southern America. This is because these regions are the most likely to be converted to agricultural sites, possibly for the production of palm oil, Newbold said.
The analysis also suggests that amphibians and reptiles could be disproportionately affected by both global warming and land-use change, when compared to mammals and birds.
Many amphibians have complex reproductive life cycles that rely on the availability of both land and freshwater. (For example, tadpoles are restricted to water while adult frogs live on land.) This reliance on multiple environments is likely to increase the group's vulnerability to climate change.
Reptiles could also be uniquely vulnerable to climate change. One reason for this is because reptiles rely on their external environment to regulate their body temperature, meaning they can overheat if temperatures are unusually high.
Bargaining with BECCS
The results show that the RCP2.6 scenario, which projects the smallest level of future climate change, leads to the second most negative land-use impacts on biodiversity.
This is largely because the scenario relies on considerable use of bioenergy with carbon capture and storage (BECCS) to limit the effects of climate change.
Put simply, BECCS involves burning biomass—such as trees and crops—to generate energy and then capturing the resulting CO2 emissions before they are released into the air.
In theory, this process could reduce the amount of CO2 in the atmosphere – making BECCS a "negative emissions technology."
However, using large-scale BECCS to limit warming to 2C could require up to 18 percent of the land surface to be converted to biomass plantations—which could pose a significant threat to biodiversity.
The new study, however, shows that when the impacts of global warming and land-use change are considered together, RCP2.6 still projects the lowest risks for biodiversity out of all of the scenarios.
This suggests that the large land-use costs associated with BECCS may be offset by the resulting reduction in climate change impacts.
However, it is important to consider that there could be other solutions for tackling climate change that would not take up large amounts of land, Newbold said. Such options would be the most beneficial for biodiversity, he added:
"The results of studies like this suggest that we should be looking for solutions that mitigate climate change that don't rely on using lots of land—because we know that has large impacts."
Reposted with permission from our media associate Carbon Brief.
By Melissa Gaskill
Two decades ago scientists and volunteers along the Virginia coast started tossing seagrass seeds into barren seaside lagoons. Disease and an intense hurricane had wiped out the plants in the 1930s, and no nearby meadows could serve as a naturally dispersing source of seeds to bring them back.
Restored seagrass beds in Virginia now provide habitat for hundreds of thousands of scallops. Bob Orth, Virginia Institute of Marine Science / CC BY 2.0<p>The paper is part of a growing trend of evidence suggesting seagrass meadows can be easier to restore than other coastal habitats.</p><p>Successful seagrass-restoration methods include <a href="https://www.sciencedirect.com/science/article/abs/pii/S0304377099000078?via%3Dihub" target="_blank">transplanting shoots</a>, <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1061-2971.2004.00314.x" target="_blank" rel="noopener noreferrer">mechanized planting</a> and, more recently, <a href="https://www.nature.com/articles/s41467-020-17438-4" target="_blank" rel="noopener noreferrer">biodegradable mats</a>. Removing threats, proximity to donor seagrass beds, planting techniques, project size and site selection all play roles in a restoration effort's success.</p><p>Human assistance isn't always necessary, though. In areas where some beds remain, seagrass can even recover on its own when stressors are reduced or removed. For example, seagrass began to recover when Tampa Bay improved its water quality by reducing nitrogen loads from runoff by roughly 90%.</p><p>But more and more, seagrass meadows struggle to hang on.</p><p>The marine flowering plants have declined globally since the 1930s and currently disappear at a rate equivalent to a football field every 30 minutes, according to the <a href="https://www.unep.org/resources/report/out-blue-value-seagrasses-environment-and-people" target="_blank" rel="noopener noreferrer">United Nations Environment Programme</a>. And research published in 2018 found the rate of decline is <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB005941" target="_blank" rel="noopener noreferrer">accelerating</a> in many regions.</p><p>The causes of decline vary and overlap, depending on the region. They include thermal stress from climate change; human activities such as dredging, anchoring and coastal infrastructure; and intentional removal in tourist areas. In addition, increased runoff from land carries sediment that clouds the water, blocking sunlight the plants need for photosynthesis. Runoff can also carry contaminants and nutrients from fertilizer that disrupt habitats and cause algal blooms.</p><p>All that damage comes with a cost.</p>
The Value of Seagrass<p>As with ecosystems like rainforests and <a href="https://therevelator.org/mangroves-climate-change/" target="_blank">mangroves</a>, loss of seagrass increases carbon dioxide emissions. And that spells trouble not just for certain habitats but for the whole planet.</p><p>Although seagrass covers at most 0.2% of the seabed, it <a href="https://www.unenvironment.org/news-and-stories/story/seagrass-secret-weapon-fight-against-global-heating" target="_blank">accounts for 10%</a> of the ocean's capacity to store carbon and soils, and these meadows store carbon dioxide an estimated 30 times faster than most terrestrial forests. Slow decomposition rates in seagrass sediments contribute to their <a href="https://www.researchgate.net/publication/238506081_Assessing_the_capacity_of_seagrass_meadows_for_carbon_burial_Current_limitations_and_future_strategies" target="_blank" rel="noopener noreferrer">high carbon burial rates</a>. In Australia, according to <a href="https://onlinelibrary.wiley.com/doi/10.1111/gcb.15204" target="_blank" rel="noopener noreferrer">research</a> by scientists at Edith Cowan University, loss of seagrass meadows since the 1950s has increased carbon dioxide emissions by an amount equivalent to 5 million cars a year. The United Nations Environment Programme reports that a 29% decline in seagrass in Chesapeake Bay between 1991 and 2006 resulted in an estimated loss of up to 1.8 million tons of carbon.</p>
Eelgrass in the river delta at Prince William Sound, Alaska. Alaska ShoreZone Program NOAA / NMFS / AKFSC; Courtesy of Mandy Lindeberg / NOAA / NMFS / AKFSC<p>Seagrasses also protect costal habitats. A healthy meadow slows wave energy, reduces erosion and lowers the risk of flooding. In Morro Bay, California, a 90% decline in the seagrass species known as eelgrass caused extensive erosion, according to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0272771420303528?via%3Dihub" target="_blank" rel="noopener noreferrer">paper</a> from researchers at California Polytechnic State University.</p><p>"Right away, we noticed big patterns in sediment loss or erosion," said lead author Ryan Walter. "Many studies have shown this on individual eelgrass beds, but very few studies looked at it on a systemwide scale."</p><p>In the tropics, seagrass's natural protection can reduce the need for expensive and often-environmentally unfriendly <a href="https://www.nioz.nl/en/news/zeegras-spaart-stranden-en-geld" target="_blank" rel="noopener noreferrer">beach nourishments</a> regularly conducted in tourism areas.</p><p>Seagrass ecosystems improve water quality and clarity, filtering particles out of the water column and preventing resuspension of sediment. This role could be even more important in the future. By producing oxygen through photosynthesis, meadows could help offset decreased oxygen levels caused by warmer water temperatures (oxygen is less soluble in warm than in cold water).</p><p>The meadows also provide vital habitat for a wide variety of marine life, including fish, sea turtles, birds, marine mammals such as manatees, invertebrates and algae. They provide nursery habitat for <a href="https://wedocs.unep.org/bitstream/handle/20.500.11822/32636/seagrass.pdf?sequence=1&isAllowed=y" target="_blank" rel="noopener noreferrer">roughly 20%</a> of the world's largest fisheries — an <a href="https://www.floridamuseum.ufl.edu/science/seagrass-meadows-harbor-wildlife-for-centuries/" target="_blank" rel="noopener noreferrer">estimated 70%</a> of fish habitats in Florida alone.</p><p>Conversely, their disappearance can contribute to die-offs of marine life. The loss of more than 20 square miles of seagrass in Florida's Biscayne Bay may have helped set the stage for a widespread <a href="https://www.wlrn.org/2020-08-14/the-seagrass-died-that-may-have-triggered-a-widespread-fish-kill-in-biscayne-bay" target="_blank">fish kill</a> in summer 2020. Lack of grasses to produce oxygen left the basin more vulnerable when temperatures rose and oxygen levels dropped as a result, says Florida International University professor Piero Gardinali.</p>
Damaged Systems, a Changing Climate<p>Governments and conservationists around the world have already put a lot of effort into coastal restoration efforts. And that's helped some seagrass populations.</p><p>Where stressors remain, though, restoration grows more complicated. <a href="https://www.rug.nl/research/portal/en/publications/the-future-of-seagrass-ecosystem-services-in-a-changing-world(3a8c56db-7bed-4c9e-ac7f-c72453e2a102).html" target="_blank">Research</a> published this September found that only 37% of seagrass restorations have survived. Newly restored meadows remain vulnerable to the original stressors that depleted them, as well as to storms — and <a href="https://www.ecowatch.com/tag/climate-crisis">climate change</a>.</p>
Seagrass in Dry Tortugas National Park, Florida. Alicia Wellman / Florida Fish and Wildlife / CC BY-NC-ND 2.0<p>In Chesapeake Bay a cold-water species of seagrass is currently hitting its heat limit, especially in summer, according to Alexander Challen Hyman of University of Florida's School of Natural Resources and Environment. As waters continue to warm due to climate change, the species likely will disappear there.</p><p>Climate-driven sea-level rise complicates the problem as well. Seagrasses thrive at specific depths — too shallow and they dry out or are eaten, too deep and there isn't enough light for photosynthesis.</p>
But There’s Good News, Too<p>Luckily, left to its own devices, a seagrass meadow can flourish for hundreds of years, according to a <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2019.1861" target="_blank" rel="noopener noreferrer">paper</a> published last year by Hyman and other researchers from the University of Florida. The researchers arrived at their conclusion by looking at shells of living mollusks and fossil shells to estimate the ages of meadows in Florida's Big Bend region on the Gulf Coast.</p><p>That area has extensive, relatively pristine seagrass meadows. "Our motivation was to understand the past history of these systems, and shells store a lot of history," said co-author Michal Kowalewski.</p><p>A high degree of similarity between living and dead shells indicates a stable area, while a mismatch suggests an area shifted from seagrass to barren sand. The researchers found that long-term accumulations of shells resembled living ones, suggesting that the seagrass habitats have been stable over time.</p><p>That stability allows biodiversity to thrive, creating conditions where specialist species can survive and flourish, according to Hyman.</p><p>Discovering the long-term stability of seagrass meadows has implications for choosing restoration sites, Kowalewski notes.</p><p>"There must be reasons they thrive in one place, while a mile away they don't and fossil data says they probably never did," he said. "If we remove a seagrass patch, we cannot hope to plant it somewhere else. It's not just the seagrass that is special. The location at which it's found is special, too."</p><p>A better approach is conserving these habitats in the first place, but we're not doing enough of that right now. The UN reports that marine protected areas safeguard just 26% of recorded seagrass meadows, compared with 40% of coral reefs and 43% of mangroves.</p>
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