A new map shows where carbon needs to stay in nature to avoid climate disaster

Over decades, centuries and millennia, the steady skyward climb of redwoods, the tangled march of mangroves along tropical coasts and the slow submersion of carbon-rich soil in peatlands has locked away billions of tons of carbon.

If these natural vaults get busted open, through deforestation or dredging of swamplands, it would take centuries before those redwoods or mangroves could grow back to their former fullness and reclaim all that carbon. Such carbon is “irrecoverable” on the timescale — decades, not centuries — needed to avoid the worst impacts of climate change, and keeping it locked away is crucial.

Now, through a new mapping project, scientists have estimated how much irrecoverable carbon resides in peatlands, mangroves, forests and elsewhere around the globe — and which areas need protection.

The new estimate puts the total amount of irrecoverable carbon at 139 gigatons, researchers report November 18 in Nature Sustainability. That’s equivalent to about 15 years of human carbon dioxide emissions at current levels. And if all that carbon were released, it’s almost certainly enough to push the planet past 1.5 degrees Celsius of warming above preindustrial levels.
“This is the carbon we must protect to avert climate catastrophe,” says Monica Noon, an environmental data scientist at Conservation International in Arlington, Va. Current efforts to keep global warming below the ambitious target of 1.5 degrees C require that we reach net-zero emissions by 2050, and that carbon stored in nature stays put (SN:12/17/18). But agriculture and other development pressures threaten some of these carbon stores.

To map this at-risk carbon, Noon and her colleagues combined satellite data with estimates of how much total carbon is stored in ecosystems vulnerable to human incursion. The researchers excluded areas like permafrost, which stores lots of carbon but isn’t likely to be developed (although it’s thawing due to warming), as well as tree plantations, which have already been altered (SN: 9/25/19). The researchers then calculated how much carbon would get released from land conversions, such as clearing a forest for farmland.

That land might store varying amounts of carbon, depending on whether it becomes a palm oil plantation or a parking lot. To simplify, the researchers assumed cleared land was left alone, with saplings free to grow where giants once stood. That allowed the researchers to estimate how long it might take for the released carbon to be reintegrated into the land. Much of that carbon would remain in the air by 2050, the team reports, as many of these ecosystems take centuries to return to their former glory, rendering it irrecoverable on a timescale that matters for addressing climate change.
Releasing that 139 gigatons of irrecoverable carbon could have irrevocable consequences. For comparison, the United Nations’ Intergovernmental Panel on Climate Change estimates that humans can emit only 109 more gigatons of carbon to have a two-thirds chance of keeping global warming below 1.5 degrees C. “These are the places we absolutely have to protect,” Noon says.

Approximately half of this irrecoverable carbon sits on just 3.3 percent of Earth’s total land area, equivalent to roughly the area of India and Mexico combined. Key areas are in the Amazon, the Pacific Northwest, and the tropical forests and mangroves of Borneo. “The fact that it’s so concentrated means we can protect it,” Noon says.

Roughly half of irrecoverable carbon already falls within existing protected areas or lands managed by Indigenous peoples. Adding an additional 8 million square kilometers of protected area, which is only about 5.4 percent of the planet’s land surface, would bring 75 percent of this carbon under some form of protection, Noon says.

“It’s really important to have spatially explicit maps of where these irrecoverable carbon stocks are,” says Kate Dooley, a geographer at the University of Melbourne in Australia who wasn’t involved in the study. “It’s a small percentage globally, but it’s still a lot of land.” Many of these dense stores are in places at high risk of development, she says.

“It’s so hard to stop this drive of deforestation,” she says, but these maps will help focus the efforts of governments, civil society groups and academics on the places that matter most for the climate.

Earth is reflecting less light. It’s not clear if that’s a trend

The amount of sunlight that Earth reflects back into space — measured by the dim glow seen on the dark portions of a crescent moon’s face — has decreased measurably in recent years. Whether the decline in earthshine is a short-term blip or yet another ominous sign for Earth’s climate is up in the air, scientists suggest.

Our planet, on average, typically reflects about 30 percent of the sunlight that shines on it. But a new analysis bolsters previous studies suggesting that Earth’s reflectance has been declining in recent years, says Philip Goode, an astrophysicist at Big Bear Solar Observatory in California. From 1998 to 2017, Earth’s reflectance declined about 0.5 percent, the team reported in the Sept. 8 Geophysical Research Letters.

Using ground-based instruments at Big Bear, Goode and his colleagues measured earthshine — the light that reflects off our planet, to the moon and then back to Earth — from 1998 to 2017. Because earthshine is most easily gauged when the moon is a slim crescent and the weather is clear, the team collected a mere 801 data points during those 20 years, Goode and his colleagues report.

Much of the decrease in reflectance occurred during the last three years of the two-decade period the team studied, Goode says. Previous analyses of satellite data, he and his colleagues note, hint that the drop in reflectance stems from warmer temperatures along the Pacific coasts of North and South America, which in turn reduced low-altitude cloud cover and exposed the underlying, much darker and less reflective seas.
“Whether or not this is a long-term trend [in Earth’s reflectance] is yet to be seen,” says Edward Schwieterman, a planetary scientist at University of California, Riverside, who was not involved in the new analysis. “This strengthens the argument for collecting more data,” he says.

Decreased cloudiness over the eastern Pacific isn’t the only thing trimming Earth’s reflectance, or albedo, says Shiv Priyam Raghuraman, an atmospheric scientist at Princeton University. Many studies point to a long-term decline in sea ice (especially in the Arctic), ice on land, and tiny pollutants called aerosols — all of which scatter sunlight back into space to cool Earth.

With ice cover declining, Earth is absorbing more radiation. The extra radiation absorbed by Earth in recent decades goes toward warming the oceans and melting more ice, which can contribute to even more warming via a vicious feedback loop, says Schwieterman.

Altogether, Goode and his colleagues estimate, the decline in Earth’s reflectance from 1998 to 2017 means that each square meter of our planet’s surface is absorbing, on average, an extra 0.5 watts of energy. For comparison, the researchers note in their study, planet-warming greenhouse gases and other human activity over the same period boosted energy input to Earth’s surface by an estimated 0.6 watts of energy per square meter. That means the decline in Earth’s reflectance has, over that 20-year period, almost doubled the warming effect our planet experienced.

5 cool things to know about NASA’s Lucy mission to the Trojan asteroids

For the first time, a spacecraft is headed to Jupiter’s odd Trojan asteroids. What Lucy finds there could provide a fresh peek into the history of the solar system.

“Lucy will profoundly change our understanding of planetary evolution in our solar system,” Adriana Ocampo, a planetary scientist at NASA Headquarters in Washington, D.C., said at a news briefing October 14.

The mission is set to launch from the Kennedy Space Center at Cape Canaveral, Fla., as early as October 16. Live coverage will air on NASA TV beginning at 5 a.m. EDT, in anticipation of a 5:34 a.m. blast off.

The Trojan asteroids are two groups of space rocks that are gravitationally trapped in the same orbit as Jupiter around the sun. One group of Trojans orbits ahead of Jupiter; the other follows the gas giant around the sun. Planetary scientists think the Trojans could have formed at different distances from the sun before getting mixed together in their current homes. The asteroids could also be some of the oldest and most pristine objects in the solar system.

The mission will mark several other firsts, from the types of objects it will visit to the way it powers its instruments. Here are five cool things to know about our first visit to the Trojans.

  1. The Trojan asteroids are a solar system time capsule.
    The Trojans occupy spots known as Lagrangian points, where the gravity from the sun and from Jupiter effectively cancel each other out. That means their orbits are stable for billions of years.

“They were probably placed in their orbits by the final gasp of the planet formation process,” the mission’s principal investigator Hal Levison, a planetary scientist at Southwest Research Institute in Boulder, Colo., said September 28 in a news briefing.

But that doesn’t mean the asteroids are all alike. Scientists can tell from Earth that some Trojans are gray and some are red, indicating that they might have formed in different places before settling in their current orbits. Maybe the gray ones formed closer to the sun, and the red ones formed farther from the sun, Levison speculated.

Studying the Trojans’ similarities and differences can help planetary scientists tease out whether and when the giant planets moved around before settling into their present positions (SN: 4/20/12). “This is telling us something really fundamental about the formation of the solar system,” Levison said.

  1. The spacecraft will visit more individual objects than any other single spacecraft.
    Lucy will visit eight asteroids, including their moons. Over its 12-year mission, it will visit one asteroid in the main asteroid belt between Mars and Jupiter, and seven Trojans, two of which are binary systems where a pair of asteroids orbit each other.

“We are going to be visiting the most asteroids ever with one mission,” planetary scientist Cathy Olkin, Lucy’s deputy principal investigator, said in the Oct. 14 briefing.

The spacecraft will observe the asteroids’ composition, shape, gravity and geology for clues to where they formed and how they got to the Lagrangian points.

The spacecraft’s first destination, in April 2025, will be an asteroid in the main belt. Next, it will visit five asteroids in the group of Trojans that orbit the sun ahead of Jupiter: Eurybates and its satellite Queta in August 2027; Polymele in September 2027; Leucus in April 2028; and Orus in November 2028. Finally, the spacecraft will shift to Jupiter’s other side and visit the twin asteroids Patroclus and Menoetius in the trailing group of space rocks in March 2033.

The spacecraft won’t land on any of its targets, but it will swoop within 965 kilometers of their surfaces at speeds of 3 to 5 meters per second relative to the asteroids’ speed through space.

There’s no need to worry about collisions while zipping through these asteroid clusters, Levison said. Although there are about 7,000 known Trojans, they’re very far apart. “If you were standing on any one of our targets, you wouldn’t be able to tell you were part of the swarm,” he said.

  1. Lucy will have a weird flight path.
    In order to make so many stops, Lucy will need to take a complex path. First, the spacecraft will swoop past Earth twice to get a gravitational boost from our planet that will help propel it onward to its first asteroid.

The closest Earth flyby, in October 2022, will take it within 300 kilometers of the planet’s surface, closer than the International Space Station, the Hubble Space Telescope and many satellites, Olkin said. Observers on Earth might even be able to see it. “I’m hoping to go near where it flies past and look up and see Lucy flying by a year from now,” she said.

Then in December 2030, after more than a year exploring the “leading” swarm of Trojans, Lucy will come back to the vicinity of Earth for one more boost. That final gravitational slingshot will send the spacecraft to the other side of the sun to visit the “trailing” swarm. This will make Lucy the first spacecraft ever to venture to the outer solar system and come back near Earth again.

  1. Lucy will travel farther from the sun than any other solar-powered craft.
    Another record Lucy will break has to do with its power source: the sun. Lucy will run on solar power out to 850 million kilometers away from the sun, making it the farthest-flung solar powered spacecraft ever.

To accomplish that, Lucy has a pair of enormous solar arrays. Each 10-sided array is more than 7.3 meters across and includes about 4,000 solar cells per panel, Lucy project manager Donya Douglas-Bradshaw said in a news briefing on October 13. Standing on one end, Lucy and its solar panels would be as tall as a five-story building.

“It’s a very intricate, sophisticated design,” she said. The advantage of using solar power is that the team can adjust how much power the spacecraft needs based on how far from the sun it is.

  1. The inspiration for Lucy’s name is decidedly earthbound.
    NASA missions are often named for famous scientists, or with acronyms that describe what the mission will do. Lucy, on the other hand, is named after a fossil.

The idea that the Trojans hold secrets to the history of the solar system is part of how the mission got its unusual name. To understand, go back to 1974, when paleoanthropologist Donald Johanson and a graduate student discovered a fossil of a human ancestor who had lived 3.2 million years ago. After listening to the Beatles song “Lucy in the Sky with Diamonds” at camp that night, Johanson’s team named the fossil hominid “Lucy.” (In a poetic echo, the first asteroid the Lucy spacecraft will visit is named Donaldjohanson.)

Planetary scientists hope the study of the Trojans will revolutionize our understanding of the solar system’s history in the same way that studying Lucy’s fossil revolutionized our understanding of human history.

“We think these asteroids are fossils of solar system formation,” Levison said. So his team named the spacecraft after the fossil.

The spacecraft even carries a diamond in one of its instruments, to help split beams of light. Said planetary scientist Phil Christensen of Arizona State University in Tempe at the Oct. 14 briefing: “We truly are sending a diamond into the sky with Lucy.”

What the Perseverance rover’s quiet landing reveals about meteor strikes on Mars

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.
But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”