Earth Humanity39;s greatest ally against climate change is the itself
Earth Earth ally change climate against greatest the Humanity's is itself
Thu, 22 Apr 2021 09:00:00 -0700
Humanity's greatest ally against climate change is the Earth itself · Ecosystems can draw down carbon and buffer us from the worst effects of climate change — but
Spring has returned to the California coast, bringing with it abundant sunshine and calmer seas. Storm-tossed sands settle. Nourishing cold water floods in from offshore. It is time for a climate superhero to emerge.
Giant kelp is among the best organisms on the planet for taking planet-warming gases out of the atmosphere. Buoyed by small, gas-filled bulbs called “bladders,” these huge algae grow toward the ocean surface at a pace of up to two feet per day. Their flexible stems and leafy blades form a dense underwater canopy that can store 20 times as much carbon as an equivalent expanse of terrestrial trees.
And when the fierce waves of winter come and kelp is ripped from its rocky anchors and washed out to the deep sea, that carbon gets buried on the ocean floor. It may stay there for centuries, even millennia, locking away more greenhouse gases than 20 million American homes use in a year.
Yet this powerful force for planetary protection is under siege. Warming waters and worsening storms caused by climate change have weakened the kelp forests. Sewage and sediment spill onto them from cities on the shore. Most significantly, the demise of important predators such as otters and sea stars has led to an explosion in the population of sea urchins, which eat kelp. Huge swaths of underwater forest are being replaced by urchin “barrens” — denuded landscapes, desolate but for the spiky, spherical animals. Eventually, even the urchins start to starve.
Humans have put our planet on a path toward disaster. If people keep polluting at the current rate, scientists say, climate change will cause prolonged droughts, devastating storms, collapsing ecosystems and vanishing species. Coastal cities will be deluged by sea level rise; widespread food and water shortages will lead to the deaths of millions. To avoid this fate, civilization must rapidly transform — cutting carbon emissions 40 percent by 2030 and reaching “net zero” by the middle of the century.
The Earth itself is our greatest ally in this effort. Ecosystems like California’s kelp forests absorb about half of the greenhouse gases humans emit, studies show. Without them, warming would be even worse. Nature shields us from the worst consequences of our own actions, forgiving the sins we refuse to repent.
But it cannot endure endless abuse. Life on Earth is threatened by overexploitation, pollution and habitat degradation, in addition to rising temperatures. The fraction of the planet that is undisturbed by human activities shrinks every year.
If we hope to solve climate change, humanity must also address this biodiversity crisis — restoring ecosystems and the creatures that inhabit them. Otherwise, our species risks becoming like the sea urchins: agents of our own suffering, looters of the only home we have.
One way to revitalize ecosystems: protect the ground they grow from.
Think of the soft, spongy soil of an old-growth woodland. Here, a towering oak tree draws up water and nutrients via threadlike fungi attached to its roots. In exchange, the fungi take sugar from the oak, funneling carbon from the air into the ground.
Now imagine a leaf from that oak drifting slowly to the forest floor. Perhaps it becomes food for an earthworm. Then microbes attack the earthworm’s droppings, breaking down the residue further still.
Eventually, the carbon that was once a leaf can become trapped in clods of earth. Other atoms may form strong chemical bonds with minerals like iron, which prevents them from reacting with oxygen and returning to the air. Under the right conditions, carbon might stay locked away in dense, dark earth for centuries. Soils contain more carbon than the entire atmosphere and all the world’s plants combined.
This makes soil both a ticking time bomb and an overlooked climate solution, said Asmeret Asefaw Berhe, a soil biogeochemist at the University of California at Merced. As the world warms, the carbon contained in frozen Arctic peatlands is at risk of release. As people till the ground for agriculture and excavate land for development, any trapped carbon is unleashed into the air. At least a third of all soils on Earth have been degraded by human activities.
“And because soil is such an important reservoir,” Berhe said, “a small change in the release of that carbon can lead to a big change in the concentrations of greenhouse gases in the atmosphere.”
But soil can be rehabilitated, making it a carbon stockpile once more. Farmers can reduce or eliminate the practice of tilling — which involves turning over the top layer of soil, displacing essential microbes and increasing erosion. By allowing fields to lie fallow, or planting cover crops, they can return nutrients to the soil. Adding carbon-rich materials such as compost or biochar (a form of charcoal produced by burning organic matter in an oxygen-free environment) can boost carbon storage and enhance soil health.
A 2020 analysis in the journal Nature Sustainability found that better soil stewardship could reduce emissions by at least 5.5 gigatons of carbon dioxide each year — about 15 percent of current annual emissions.
“Once that happens,” Berhe said, “it’s not just the carbon status of the soil that’s improved. The soil literally becomes softer. It holds more water and nutrients. It’s easier for plants to grow in … and serve as a home for the most abundant and diverse group of organisms that we know of.”
Enhancing carbon in soils is just the beginning. In 2017, an international team of scientists set out to determine how much carbon the planet could pull out of the atmosphere, if humans would only give it a chance. In a study in the Proceedings of the National Academy of Sciences (PNAS), they concluded natural climate systems are capable of storing almost 24 gigatons of carbon dioxide per year — roughly two thirds of what people emit. About half of that sequestration would be cost-effective, meaning enacting the necessary protections would cost less than the consequences of keeping that carbon in the air.
Of the climate solutions they studied, few delivered more carbon bang per buck than mangroves — lush systems of salt-tolerant shrubs and trees that thrive where freshwater rivers spill into the sea. Though these forests occupy just 0.5 percent of the Earth’s shorelines, they account for 10 percent of the coast’s carbon storage capacity.
And they do more than just draw down carbon. With their luxuriant canopies and pillar-like roots extending deep into brackish water, mangroves provide shelter for small fish and help clean coasts. When storms strike a shoreline, they lessen the force of the waves.
But the unique ecosystems are too often dismissed as unproductive swamps, good for no one but the mosquitoes. In the past half-century, more than a quarter of the world’s mangroves have been destroyed — drained for development, converted for shrimp farms, poisoned by fertilizer and drowned by dammed-up streams. Activists who seek to protect the mangroves have found themselves the target of harassment, lawsuits and physical violence.
“Human nature needs nature,” said Alfredo Quarto, executive director of the Mangrove Action Project. “But we don’t see it, we don’t see how integrated we are.”
“If we manage mangroves for making profits for the few at the cost of the many and the cost of our future,” he continued, “we’re killing ourselves.”
Quarto’s organization has developed a community-based process to restore depleted mangroves to their former glory. Environmentalists work with residents to identify the causes of decline — pollution from nearby farms, blockages in streams — and fix the problems so the forests can rebound on their own.
At one site in El Salvador, Quarto said, mangrove restoration efforts have revitalized the local fishing industry, boosted tourism and protected endangered sea turtles on the brink of extinction. Seen in satellite photos, the area is a richer, deeper green than any other part of the coast. From the ground, it is an aquatic Eden, perfumed by the mangroves’ bell-shaped flowers, noisy with the snapping of shrimp and the songs of birds.
“There is an alternative,” Quarto said. “That’s the thing we try to instill in people around the world.”
This October, global leaders will gather in Kunming, China, for the 15th conference of parties to the United Nation’s Convention on Biological Diversity. There they are expected to hammer out a plan for protecting ecosystems — a “Paris agreement for biodiversity,” in the words of one scientist.
Several nations, including the United States, will advocate for setting aside 30 percent of the world’s land and oceans for nature by the end of the decade. Such protections would go a long way toward reducing carbon emissions, as well as boosting animal and plant populations and improving planetary health.
Yet the Earth cannot compensate for all of humanity’s pollution, said William Schlesinger, former dean of Duke University’s School of the Environment and a co-author on the 2017 PNAS study. Unless people also reduce the amount of greenhouse gases we emit, no amount of ecological restoration will save us.
“The bottom line is we’ve got to get off of using fossil fuels in transportation and heating and lighting and everything else,” Schlesinger said.
In public talks, he puts it this way: “It’s easier to patch a hole in a bag than to pick up the marbles that fall out.”
Nowhere is that more evident than in the Arctic, where temperatures are rising faster than anywhere else on Earth.
Since the end of the last ice age, the frozen expanse at the top of the world has acted as a protective shield. During the summer, when the sun shines 24 hours a day, Arctic sea ice reflects about two-thirds of the light that hits it back into space. By contrast, the dark open ocean absorbs the majority of the sun’s heat.
“It’s like the air conditioning unit of our planet,” said Melinda Webster, a sea ice specialist at the University of Alaska Fairbanks.
If the Arctic loses its perpetual ice cover, it would add half a degree Celsius of warming to the global average temperature, studies suggest. The world is hurtling toward that milestone. Since 1979, the volume of ice left at the end of the summer has shrunk about 75 percent.
“Sea ice is such a powerful thing,” Webster said. “When you see its expansive, vast scale — how dynamic it is, how much it can change by the season — and you realize how critically important it is, the prospect of losing it does frighten me.”
There is just one way to save it, she said: by stopping global warming. Only by ending the use of fossil fuels and eliminating greenhouse gas emissions can people prevent the Arctic from heating further and give the ice a chance to recover.
If we do nothing, models indicate, it will be a matter of decades before the summertime Arctic is ice-free for the first time in human history. Sea levels will surge, coastal communities will be deluged, and we will no longer have the planet’s air conditioning unit to help us cool our world down.
This is perhaps the most important lesson nature holds for us. Though Earth has undergone countless changes in the past 4.6 billion years, we humans have experienced only a narrow band of the planet’s possibilities. Our species evolved and our civilization was built under fairly stable climate conditions. When things changed, they changed slowly, giving us time to adapt.
And we have never had to adapt to anything like the world we live in now. The last time atmospheric carbon concentrations were this high, humanity’s ancestors hadn’t even learned to stand on two legs. The last time average global temperatures changed this much, this fast — well, scientists don’t think that’s ever happened.
The rapid transformation of our planet doesn’t just endanger ecosystems; humanity will suffer. People have never lived on a planet without mangroves, or peatlands, or summertime ice. We’ve never had to go without the benefits the Earth provides.
Recovery is still possible — the kelp forests are proof. Along the California coast, marine protected areas have been established to protect kelp habitat. Fishermen are harvesting excess urchins from the barrens. Scientists are working on developing more heat-tolerant strains of giant algae, and environmental groups are restoring reefs and replanting the sea beds where kelp once grew.
Slowly, in scattered areas, the forest has started to return. The canopies are thickening; fish swim once more amid their swaying stems. Even the urchins are plumper and healthier — a reminder that all life depends on diversity.
Nature doesn’t only need us to save it. Humanity needs nature if we hope to survive.
Thu, 22 Apr 2021 09:00:00 -0700
The carbon, prevented from being buried even deeper in Earth, will eventually escape back into the atmosphere—where it could help warm the planet
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Researchers sample natural springs near Irazú volcano in Costa Rica.
A few kilometers below our feet lies a hidden world of microbes whose chemical reactions are shaping the long-term habitability of the planet. A new study suggests some of these microbes are siphoning off massive amounts of carbon as it enters Earth, using it to fuel their own sunless ecosystems. The carbon, prevented from being buried even deeper in Earth, will eventually escape back into the atmosphere—where it could help warm the planet. Researchers say the microbes represent an overlooked factor in efforts to balance Earth’s deep carbon cycle.
“It’s a really big leap forward,” says Georgia Institute of Technology biogeochemist Jennifer Glass, who was not involved in the study. She adds that this is one of the first papers to show how subterranean microbes can trap globally significant amounts of carbon.
Warming from human emissions of carbon dioxide (CO2) will be the deciding factor for surface temperatures in the coming centuries. But there is also a deeper carbon cycle, one that plays out over hundreds of millions of years. Slabs of ocean crust dive into Earth’s mantle at subduction zones, taking carbon down with them for long-term storage in the mantle. Some of this carbon, dissolved in rising blobs of magma and gasses, gets re-emitted at volcanoes. But much of what goes down doesn’t come back up, and researchers still don’t fully understand why.
Scientists found some of that missing carbon in 2017, when they examined gasses and fluids bubbling up from more than 20 hot springs in Costa Rica. The springs were 40 to 120 kilometers above the subduction zone where the Cocos Plate dives beneath Central America. Scientists found that a portion of the CO2 that goes down with the descending plate is turned into rock and never reaches the deep mantle or the atmosphere. But they also saw hints that more CO2 was being siphoned off the plate than rock formation alone could explain.
Now, by performing additional analyses on the hot spring samples, the same research team has found signs of chemical reactions that could only be facilitated by living things. The ratio of carbon isotopes in the samples suggests microbes are trapping the CO2 from the descending plate and turning it into organic carbon to “feed” and grow their own community. Indeed, the scientists found many bacteria in their hot spring samples that had the genes necessary for this chemical reaction. If this conversion is in fact happening—and the team’s calculations are right—microbes under this small swath of Costa Rica could be sequestering enough carbon each year to total the mass of 650 to 6500 blue whales.
“Small things add up,” says Katherine Fullerton, a microbiologist at Pellissippi State Community College who helped lead the study.
These microbes could be sequestering 2% to 22% of the carbon previously thought to reach the deep mantle, the researchers report today in Nature Geoscience. By keeping carbon close to the surface, where it is likely to eventually percolate up and re-enter the atmosphere, the microbes may be helping warm the planet over the long term, although this would require additional research to confirm.
Two percent may not have much of an effect on the deep carbon cycle, says Oliver Plümper, an expert in rock-fluid interactions at Utrecht University who was not involved in the study. But 22% would be “quite exciting.” He says this calculation constitutes an important piece to the puzzle of the deep carbon cycle, and it could impact projections of how stable Earth’s climate will remain in the long term—and how long the planet is likely to be habitable.
The researchers also found evidence for a second group of microbes that live off the organic leftovers of the carbon-sequestering bacteria. “There’s a whole world happening underneath Costa Rica,” says Karen Lloyd, co-author and microbiologist at the University of Tennessee, Knoxville. The researchers suspect similar activity is taking place in other subduction zones all over the world.
Glass says the research is off to a good start. But the next step—proving the bacteria express the genes to make proteins that modify and trap carbon—will require a lot of work, including isotope tracers to track the chemical reactions and drilling projects to glean direct samples from within Earth. And although it’s clear that these microbes are having an impact on us, they seem to function relatively independently from the surface world, Lloyd says. If the Sun were snuffed out today, these residents of the underworld likely wouldn’t know the difference.
Raleigh McElvery is a science journalist based in Cambridge, Massachusetts.
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– April 22, 2021