Climate Change Likely Drove Our Ancestors to Extinction, Study Finds
Could the climate crisis drive Homo sapiens to extinction?
If history repeats itself, then maybe. In a study published in One Earth Thursday, scientists used a combination of the fossil record and climate modeling to determine that three early human species lost a significant chunk of their climate niche right before going extinct.
"It is worrisome to discover that our ancestors, which were no less impressive in terms of mental power as compared to any other species on Earth, could not resist climate change," lead author Pasquale Raia of Università di Napoli Federico II in Napoli, Italy said in a Cell Press press release published by Phys.org. "And we found that just when our own species is sawing the branch we're sitting on by causing climate change. I personally take this as a thunderous warning message. Climate change made Homo vulnerable and hapless in the past, and this may just be happening again."
The researchers looked at six early human species that had existed from the Pliocene to the Pleistocene epochs: Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, Homo neanderthalensis and Homo sapiens. They compared 2,754 archeological findings with a climate emulator that determines rainfall, temperature and other factors over the last five million years in order to determine the climate niche for each species and whether it changed over time.
A climate niche is the sweet spot of climate conditions that are best suited to a given species' survival, New Scientist explained.
For Homo erectus, Homo heidelbergensis and Homo neanderthalensis, their climate niche shrunk just before extinction. Homo erectus, for example, went extinct during the last glacial period, which was the coldest period that species had ever experienced, the study said.
"Our findings show that despite technological innovations including the use of fire and refined stone tools, the formation of complex social networks, and — in the case of Neanderthals — even the production of glued spear points, fitted clothes, and a good amount of cultural and genetic exchange with Homo sapiens, past Homo species could not survive intense climate change," Raia said in the press release. "They tried hard; they made for the warmest places in reach as the climate got cold, but at the end of the day, that wasn't enough."
The researchers do think that, for Neanderthals, direct competition with modern humans combined with climate changes to push the species to the brink.
Other researchers who were not involved in the study cautioned that the fossil record is spotty for all of the species studied besides Neanderthals, which might mean that the species had longer lifespans or different climate niches than revealed in the study.
"Individuals belonging to these taxa lived at times, and in places, not sampled by the existing fossil record," Bernard Wood at George Washington University in Washington, DC told New Scientist.
The researchers did try to account for this somewhat by testing for two fossil records: a core fossil record including only remains known to belong to each species and an extended fossil record including unidentified remains that could have belonged to more than one species. They found that the climate niche shrunk before extinction for the three species in question no matter which record they used.
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By Robert J. Orth, Jonathan Lefcheck and Karen McGlathery
A century ago Virginia's coastal lagoons were a natural paradise. Fishing boats bobbed on the waves as geese flocked overhead. Beneath the surface, miles of seagrass gently swayed in the surf, making the seabed look like a vast underwater prairie.
Why Didn’t Seagrasses Recover Naturally?<p>Development, nutrient runoff and other human impacts have damaged marshes, mangroves, coral reefs and seagrasses in many bays and estuaries worldwide. Loss or shrinkage of these key habitats has reduced commercial fisheries, increased erosion, made coastlines more vulnerable to floods and storms and harmed many types of aquatic life. Rapid climate change has compounded these effects through <a href="https://theconversation.com/ocean-warming-has-fisheries-on-the-move-helping-some-but-hurting-more-116248" target="_blank">rising global temperatures</a>, more <a href="https://theconversation.com/more-frequent-and-intense-tropical-storms-mean-less-recovery-time-for-the-worlds-coastlines-123335" target="_blank">frequent and severe storms</a> and <a href="https://theconversation.com/as-climate-change-alters-the-oceans-what-will-happen-to-dungeness-crabs-61501" target="_blank">ocean acidification</a>.</p><p>In the late 1990s, local residents told two of us who are longtime students of seagrasses (Robert "JJ" Orth and Karen McGlathery) that they had spotted small patches of eelgrass in shallow waters off Virginia's eastern shore. For years the conventional view had been that seagrasses in this area had not recovered from the events of the 1930s because human activities had <a href="https://doi.org/10.1016/j.aquabot.2005.07.007" target="_blank">made the area inhospitable for them</a>.</p><p>But studies showed that water quality in these coastal bays was <a href="https://doi.org/10.1007/BF02782971" target="_blank" rel="noopener noreferrer">comparatively good</a>. This led us to explore a different explanation: Seeds from healthy seagrass populations elsewhere along the Atlantic coast simply weren't reaching these isolated bays. Seagrasses are underwater flowering plants, so seeds are among the main ways they reproduce and spread to new environments.</p>
Eelgrass beds were restored in four bays at the southern tip of Virginia's eastern shore on the Atlantic coast. David J. Wilcox/VIMS, CC BY-ND
Sowing a New Crop<p>From our <a href="https://doi.org/10.2307/1941597" target="_blank">earlier research</a>, we knew that when eelgrass seeds fall from the parent plant, they sink to the sea bottom quickly and don't move far from where they land. We also knew that these seeds don't germinate until late fall or early winter. This meant that if we collected the seeds in spring, when eelgrass flowers, we could hold them until the fall, helping them survive over the months in between.</p><p>We decided to try reseeding eelgrass in the areas where they were missing. Starting in 1999, we collected seeds by hand from underwater meadows in nearby Chesapeake Bay – plucking the long reproductive shoots, bringing them back to our laboratory and holding them in large outdoor seawater tanks until they released their seeds naturally. After about 10 years we started gathering the grasses using a custom-built underwater "lawn mower" to collect many more of the reproductive shoots than we could by hand.</p><p>In 2001 we sowed our first round by simply tossing seeds from a boat. Our first test plots covered 28 acres of mud flats in waters 2 to 3 feet deep. Returning the following year, we saw new seedlings sprouting up.</p><p>Each year since then, the <a href="https://www.vims.edu/" target="_blank">Virginia Institute of Marine Science</a> and the <a href="https://www.nature.org/en-us/about-us/where-we-work/united-states/virginia/" target="_blank" rel="noopener noreferrer">Nature Conservancy's Virginia Coast Reserve</a>, along with staff and students from the <a href="https://www.vcrlter.virginia.edu/" target="_blank" rel="noopener noreferrer">University of Virginia</a>, have led a team of scientists and citizens to collect and seed a combined 536 acres of bare bottom in several coastal bays.</p><p>These initial plots took off and rapidly expanded. By 2020 they covered 9,600 acres across four bays. Several factors helped them flourish. These bays are naturally flushed with cool, clean water from the Atlantic Ocean. And they lie off the tip of Virginia's eastern shore, where there is little coastal development.</p>
<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="a482c2146febd6782c99960c2b55feb8"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/K9NyfPLINtk?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span>
Sheltering Marine Life and Storing Carbon<p>Since eelgrass disappeared from these bays in the 1930s, human understanding of seagrass ecosystems has evolved. Today people don't pack their walls full of seagrass insulation but instead value different services they provide, such as habitat for fish and shellfish – including many <a href="https://doi.org/10.1111/conl.12645" target="_blank" rel="noopener noreferrer">commercially and recreationally important species</a>.</p><p>Scientists and government agencies also have recognized the importance of coastal systems in capturing and storing so-called "<a href="https://oceanservice.noaa.gov/facts/bluecarbon.html" target="_blank" rel="noopener noreferrer">blue carbon</a>." In fact, we now know that seagrasses constitute a globally significant <a href="https://doi.org/10.1038/ngeo1477" target="_blank" rel="noopener noreferrer">carbon sink</a>. They are a key tool for reducing carbon dioxide in the atmosphere and <a href="https://doi.org/10.1038/s41598-020-64094-1" target="_blank" rel="noopener noreferrer">slowing climate change</a></p><p>We are working to understand the valuable services that our restored seagrass beds provide. To our surprise, fish and invertebrates returned within only a few years as the meadows expanded. These organisms have established extensive food webs that include species ranging from tiny seahorses to 6-foot-long sandbar sharks.<br></p><p>Other benefits were equally dramatic. Water in the bays become clearer as the seagrass canopy trapped floating particles and deposited them onto the bottom, burying significant stocks of carbon and nitrogen in sediments bound by the grasses' roots. Our research is the first to verify the overall net carbon captured by seagrass, and is now being used to issue carbon offset credits that in turn <a href="https://vaseagrant.org/eelgrass-carbon-credits/" target="_blank">create more funds for restoration</a>.</p><p>One big question was whether restoring seagrasses could make it possible to bring back bay scallops, which once generated millions of dollars for the local economy. Since bay scallops no longer existed in Virginia, we obtained broodstock from North Carolina, which we have <a href="https://chesapeakebaymagazine.com/return-of-the-bay-scallop/" target="_blank">reared and released annually</a> since 2013. Regular surveys now reveal a growing population of bay scallops in the restored eelgrass, although there is still some way to go before they reach levels seen in the 1930s.</p>
Restored seagrass beds (dark areas) along Virginia's Atlantic coast, with sunlight reflecting from a small island. Jonathan Lefcheck, CC BY-ND
A Model for Coastal Restoration<p>Repairing damaged ecosystems is such an urgent mission worldwide that the United Nations has designated 2021-2030 as the <a href="https://www.decadeonrestoration.org/" target="_blank">U.N. Decade on Ecosystem Restoration</a>. We see the success we have achieved with eelgrass restoration as a prime model for similar efforts in coastal areas around the world.</p><p>Our project focused not only on reviving this essential habitat, but also on charting how restoring seagrasses affected the ecosystem and on the co-restoration of bay scallops. It provides a road map for involving scholars, nonprofits organizations, citizens and government agencies in an ecological mission where they can see the results of their work.</p><p>Recent assessments show that the restored zone only covers about 30% of the total habitable bottom in our project area. With continued support, eelgrass – and the many benefits it provides – may continue to thrive and expand well into the 21st century.</p>
By Jessica Corbett
Leaders of climate and conservation groups on Tuesday welcomed House Democrats' introduction of landmark legislation that aims to address the ocean impacts of human-caused global heating and reform federal ocean management—recognizing that, as Rep. Raúl M. Grijalva put it, "a healthy ocean is key to fighting the climate crisis."
<div id="a858f" class="rm-shortcode" data-rm-shortcode-id="99d487bc34e6e570edd2a3089e616347"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1318606309256798208" data-partner="rebelmouse"><div style="margin:1em 0">🎥 We're live! @NRDems, @RepRaulGrijalva, and @USRepKCastor are unveiling #OceanClimateAction legislation. W… https://t.co/pPdylA6cKQ</div> — Select Committee on the Climate Crisis (@Select Committee on the Climate Crisis)<a href="https://twitter.com/ClimateCrisis/statuses/1318606309256798208">1603215217.0</a></blockquote></div>
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