Climate

Coastal mangrove forests are carbon storage powerhouses, tucking away vast amounts of organic matter among their submerged, tangled root webs.

But even for mangroves, there is a “remarkable” amount of carbon stored in small pockets of forest growing around sinkholes on Mexico’s Yucatan Peninsula, researchers report May 5 in Biology Letters. These forests can stock away more than five times as much carbon per hectare as most other terrestrial forests.

There are dozens of mangrove-lined sinkholes, or cenotes, on the peninsula. Such carbon storage hot spots could help nations or companies achieve carbon neutrality — in which the volume of greenhouse gas emissions released into the atmosphere is balanced by the amount of carbon sequestered away (SN: 1/31/20).

At three cenotes, researchers led by Fernanda Adame, a wetland scientist at Griffith University in Brisbane, Australia, collected samples of soil at depths down to 6 meters, and used carbon-14 dating to estimate how fast the soil had accumulated at each site. The three cenotes each had “massive” amounts of soil organic carbon, the researchers report, averaging about 1,500 metric tons per hectare. One site, Casa Cenote, stored as much as 2,792 metric tons per hectare.

Mangrove roots make ideal traps for organic material. The submerged soils also help preserve carbon. As sea levels have slowly risen over the last 8,000 years, mangroves have kept pace, climbing atop sediment ported in from rivers or migrating inland. In the cave-riddled limestone terrain of the Yucatan Peninsula, there are no rivers to supply sediment. Instead, “the mangroves produce more roots to avoid drowning,” which also helps the trees climb upward more quickly, offering more space for organic matter to accumulate, Adame says.

As global temperatures increase, sea levels may eventually rise too quickly for mangroves to keep up (SN: 6/4/20). Other, more immediate threats to the peninsula’s carbon-rich cenotes include groundwater pollution, expanding infrastructure, urbanization and tourism. More

A sudden zag in which way the North Pole was drifting in the 1990s probably stemmed in large part from glacial melt caused by climate change, a new study suggests.

The locations of Earth’s geographic poles, where the planet’s axis pierces the surface, aren’t fixed. Instead, they wander in seasonal and near-annual cycles, largely driven by weather patterns and ocean currents (SN: 4/15/03). But in addition to moving about in relatively tight swirls just a few meters across, the poles drift over time as the planet’s weight distribution shifts and alters its rotation around its axis.

Before the mid-1990s, the North Pole had been drifting toward the western edge of Canada’s Ellesmere Island. But then the pole veered eastward by about 71 degrees toward the northeastern tip of Greenland. It’s continued to head that way, moving about 10 centimeters per year. Scientists aren’t quite sure why this shift occurred, says Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research in Beijing.

Liu and colleagues checked how well the polar drift trends matched data from previous studies on glacial melt worldwide. In particular, glacier melt in Alaska, Greenland and the southern Andes accelerated in the 1990s (SN: 9/30/20). The timing of that melting, as well as the effects it would have had on Earth’s mass distribution, suggests that glacial melt induced by climate change helped trigger the change in polar drift, the team reports in the April 16 Geophysical Research Letters.

The team’s analysis shows that while glacier melting can account for much of the change in polar drift, it doesn’t explain all of it. So other factors must be at play. With copious irrigation, for example, groundwater pumped from aquifers in one region can end up in an ocean far away (SN: 10/9/19). Like glacial melt, water management alone can’t explain the North Pole’s tack, the team reports, but it can give the Earth’s axis a substantial nudge.

The findings “reveal how much human activity can have an impact on changes to the mass of water stored on land,” says Vincent Humphrey, a climate scientist at the University of Zurich not involved in this study. And they show how large these mass shifts can be, he says. “They’re so big that they can change the axis of the Earth.” More

The under-ice trek of an autonomous underwater vehicle is giving scientists their first direct evidence for how and where warm ocean waters are threatening the stability of Antarctica’s vulnerable Thwaites Glacier. These new data will ultimately help scientists more accurately project the fate of the glacier — how quickly it is melting and retreating inland, and how far it might be from complete collapse, the team reports April 9 in Science Advances.

“We know there’s a sick patient out there, and it’s not able to tell us where it hurts,” says Eric Rignot, a glaciologist at the University of California, Irvine who was not involved in the new study. “So this is the first diagnosis.”

Scientists have eyed the Florida-sized Thwaites Glacier with mounting concern for two decades. Satellite images reveal it has been retreating at an alarming rate of somewhere between 0.6 to 0.8 kilometers per year on average since 2001, prompting some to dub it the “doomsday glacier.” But estimates of how quickly the glacier is retreating, based on computer simulations, vary widely from place to place on the glacier, Rignot and other researchers reported in Science Advances in 2019. Such uncertainty is the biggest difficulty when it comes to future projections of sea level rise (SN: 1/7/20).

The primary culprit for the rapid retreat of Thwaites and other Antarctic glaciers is known: Relatively warm ocean waters sneak beneath the floating ice shelves, the fringes of the glaciers that jut out into the ocean (SN: 9/9/20). This water eats away at the ice shelves’ underpinnings, points where the ice is anchored to the seafloor that buttress the rest of the glacier against sliding into the sea.

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Scientists have used satellite data to roughly map out what lies beneath the Thwaites ice shelf. Three deep channels carved into the seafloor snake beneath a vast water-filled cavity 120 kilometers across. But without direct measurements of the chemistry and paths the water takes to reach Thwaites’ underbelly, it’s been impossible to know where the threatening water is really coming from, how warm it is, and where it’s attacking the ice, says Anna Wåhlin, a physical oceanographer at the University of Gothenburg in Sweden.

In February and March 2019, Wåhlin and her colleagues sent the AUV Ran to traverse two of the deep channels. Gliding about 50 meters above the seafloor, the AUV collected the first direct measurements of temperature, salinity and oxygen levels in the water. From those measurements, the team was able to trace the origins of different parcels of water mixing beneath Thwaites.

Based on its chemical makeup, some of the warm water came from neighboring Pine Island Bay. “We were very surprised,” because Pine Island Bay wasn’t previously thought to be a major player in the future of Thwaites, Wåhlin says. The water mass from there was near the bottom of the cavity, about 500 meters deep, and was both less salty than the surrounding seawater and several degrees Celsius warmer than the freezing point. That’s an unstable situation, likely to create turbulence, and increasing the potential for erosion of the ice, Wåhlin says.

The find also suggests that what happens in Pine Island Bay doesn’t necessarily stay in Pine Island Bay — and that the fate of Thwaites may be closely intertwined with that of the Pine Island Glacier, another rapidly-melting river of ice, Wåhlin says. Together, the two glaciers are responsible for most of the ice and water that Antarctica is currently shedding. But while Thwaites is still pinned to the seafloor in some places, which slows its slide into the sea, those underpinnings are long gone for Pine Island, she says.

In April, scientists identified three tipping points for the precarious Pine Island glacier, thresholds it might cross as climate conditions evolve that would lead to phases of rapid, irreversible retreat. The third and final threshold, prompted by a roughly 1.2 degree Celsius increase in the temperature of ocean waters compared with current ocean temperatures, would drive the glacier to complete collapse, the team found.

An upcoming expedition Wåhlin and others are planning for January 2022 will use two AUVs to explore much farther into the cavity beneath Thwaites. Ideally, the AUVS will get several hundred kilometers closer to the shore, all the way to the grounding line, where the base of the glacier rests on land.

“That’s the key down the line,” Rignot says. Observing how water masses are interacting with the glacier’s grounding line will be crucial to understanding the future of the glacier, he says. “That’s the place where melting makes the most difference to the glacier’s stability.”

And there’s a lot that researchers still don’t know about the vast water cavity beneath Thwaites ice shelf, including its precise dimensions and the best places for AUVs to explore, he adds. “We are only just at the beginning.” More

Among the biggest questions for climate change forecasters is how atmospheric aerosols shape clouds, which can help cool the planet. Now, a new study finds that one promising strategy for understanding how aerosols and clouds interact can overestimate the cooling ability of pollution-generated clouds by up to 200 percent, researchers report in the Jan. 29 Science.
“Clouds in general, and how aerosols interact with the climate, are a big uncertainty in climate models,” says Franziska Glassmeier, an atmospheric scientist at Delft University of Technology in the Netherlands. Scientists know that aerosols — both natural, as from volcanoes, and human-caused, as from pollution — can change a cloud’s thickness, ability to scatter sunlight or how much rainfall it produces. But these complicated physical effects are difficult to simulate, so scientists have sought real-world examples to study these effects.
Enter ship tracks. Exhaust belched out of massive cargo ships crossing the oceans can form these bright lines of clouds. The tiny exhaust particles act as cloud nuclei: Water vapor condenses on the particles to form cloud droplets, the watery stuff of clouds. Ship tracks are “this prime example where we can see this cause and effect,” Glassmeier says. “Put in particles, and you can see the clouds get brighter.” Brighter clouds means that they are reflecting even more sunlight back into space.
Visible and measurable by satellite, the tracks offer a potential window into how larger-scale industrial pollution around the globe might be altering the planet’s cloudscape — and perhaps how such clouds might affect the climate. Satellite-derived analyses of ship tracks involve measuring the density of the water droplets in the clouds from the images, and calculating how the brightness of the clouds changes over time.

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To assess how well ship tracks actually represent the overall impact of pollution on clouds, Glassmeier and her colleagues compared the cooling effect of ship track clouds with that of simulated pollution-derived clouds, such as might occur over a city. In particular, the researchers wanted to simulate how both the thickness and the brightness of the clouds — and therefore their cooling effect — might evolve over time, as a result of processes like rainfall and evaporation.
The problem, the team found, is that the ship tracks don’t tell the whole story. Ship tracks are short-lived, because the source of pollution is always on the move. But industrial pollution doesn’t tend to happen in a brief pulse: Instead, there is a steady influx of particles to the atmosphere. And that difference in inputs affects how natural clouds respond over time.
In both the ship track studies and the simulations of industrial pollution, clouds initially brighten and produce a cooling effect. That’s because, in both cases, the addition of abundant aerosol particles to the atmosphere gives water vapor numerous surfaces on which to condense, creating many small water droplets that form this brighter cloud and reflect incoming radiation.
After a few hours, however, as a ship moves on, the ship track goes away, and the pulse of pollution ceases, Glassmeier says. The initial brief bit of cooling subsides as the preexisting natural clouds return to their original, nonpolluted state.
But in the case of industrial pollutants, the natural clouds don’t return to their original state, the simulations show. Rather, the pollutants hasten the clouds’ demise. That’s because the tinier aerosol-seeded droplets begin to evaporate more quickly than larger, natural cloud droplets would. This increased evaporation thins the original cloud, allowing more heat through than if the pollutants never arrived. And that can ultimately have an overall warming, rather than cooling, effect on the climate, the team says.
“There is this timescale effect that needs to be taken into account,” Glassmeier says. Relying solely on ship track data to understand all sources of pollution misses this gradual thinning effect. “I wouldn’t throw all the ship track data away; we just need to interpret it in a new way.” Current climate models tend to omit this thinning effect, she says.
The new study is “really useful for helping to interpret aerosol-cloud relationships in satellite data,” says Edward Gryspeerdt, an atmospheric physicist at Imperial College London who was not involved in the study. It “demonstrates that the cloud response to aerosols is not instant, but evolves over time.”
Scientists have been aware that ship tracks may not lead to cooling, says Graeme Stephens, an atmospheric scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. For example, Stephens notes that he and others have previously found that ship tracks can speed up cloud thinning by increasing the rate of evaporation at the tops of the clouds, while at the same time suppressing rainfall, which maintains some of the cloud’s thickness. These two competing responses make determining a cloud’s ultimate fate tricky.
But what ship tracks can do is act as “a controlled laboratory of sorts,” Stephens says. They “offer us a way to examine aerosol influences on clouds in a direct, concrete way.” More

An analysis of the successes and failures of past electrical power projects across Africa suggests the continent isn’t likely to go green before 2030. More

The New Climate WarMichael E. MannPublic Affairs, $29
Sometime around the fifth century B.C., the Chinese general and military strategist Sun Tzu wrote in his highly quotable treatise The Art of War, “If you know the enemy and know yourself, you need not fear the result of a hundred battles.”
In The New Climate War, climate scientist Michael Mann channels Sun Tzu to demystify the myriad tactics of “the enemy” — in this case, “the fossil fuel companies, right-wing plutocrats and oil-funded governments” and other forces standing in the way of large-scale action to combat climate change. “Any plan for victory requires recognizing and defeating the tactics now being used by inactivists as they continue to wage war,” he writes.
Mann is a veteran of the climate wars of the 1990s and early 2000s, when the scientific evidence that the climate is changing due to human emissions of greenhouse gases was under attack. Now, with the effects of climate change all around us (SN: 12/21/20), we are in a new phase of those wars, he argues. Outright denial has morphed into “deception, distraction and delay.”
Such tactics, he says, are direct descendants of earlier public relations battles over whether producers or consumers must bear ultimate responsibility for, say, smoking-related deaths. When it comes to the climate, Mann warns, an overemphasis on individual actions could eclipse efforts to achieve the real prize: industrial-scale emissions reductions.

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He pulls no punches, calling out sources of “friendly fire” from climate advocates who he says divide the climate community and play into the “enemy’s” hands. These advocates include climate purists who lambaste scientists for flying or eating meat; science communicators who push fatalistic visions of catastrophic futures; and idealistic technocrats who advocate for risky, pie-in-the-sky geoengineering ideas. All, Mann says, distract from what we can do in the here and now: regulate emissions and invest in renewable energy.
The New Climate War’s main focus is to combat psychological warfare, and on this front, the book is fascinating and often entertaining. It’s an engrossing mix of footnoted history, acerbic political commentary and personal anecdotes. As far as what readers can do to assist in the battle, Mann advocates four strategies: Disregard the doomsayers; get inspired by youth activists like Greta Thunberg; focus on educating the people who will listen; and don’t be fooled into thinking it’s too late to take action to change the political system.
Buy The New Climate War from Amazon.com. Science News is a participant in the Amazon Services LLC Associates Program. Please see our FAQ for more details. More

2020 is in a “dead heat” with 2016 for the hottest year on record, scientists with NASA and the National Oceanic and Atmospheric Administration announced January 14.
Based on ocean temperature data from buoys, floats and ships, as well as temperatures measured over land at weather stations around the globe, the U.S. agencies conducted independent analyses and arrived at a similar conclusion.
NASA’s analysis showed 2020 to be slightly hotter, while NOAA’s showed that 2016 was still slightly ahead. But the differences in those assessments are within margins of error, “so it’s effectively a statistical tie,” said NASA climatologist Gavin Schmidt of the Goddard Institute for Space Studies in New York City at a Jan. 14 news conference.
NOAA climate scientist Russell Vose, who is also based in New York City, described in the news conference the extreme warmth that occurred over land last year, including a months-long heat wave in Siberia (SN: 12/21/20). Europe and Asia recorded their hottest average temperatures on record in 2020, with South America recording its second warmest.
It’s possible that 2020’s temperatures in some areas might have been even higher if not for massive wildfires. Vose noted that smoke lofted high into the stratosphere as a result of Australia’s intense fires in early 2020 may have slightly decreased temperatures in the Northern Hemisphere, though this is not yet known (SN: 12/15/20).
The ocean-climate pattern known as the El Niño Southern Oscillation can boost or decrease global temperatures, depending on whether it’s in an El Niño or La Niña phase, respectively, Schmidt said (SN: 5/2/16). The El Niño phase was waning at the start of 2020, and a La Niña was starting, so the overall impact of this pattern was muted for the year. 2016, on the other hand, got a large temperature boost from El Niño. Without that, “2020 would have been by far the warmest year on record,” he said.
But placed in the bigger picture, these rankings “don’t tell the whole story,” Vose said. “The last six to seven years really stand out above the rest of the record, suggesting the kind of rapid warming we’re seeing. [And] each of the past four decades was warmer than the one preceding it.” More

A more acidic ocean could give some species a glow-up.
As the pH of the ocean decreases as a result of climate change, some bioluminescent organisms might get brighter, while others see their lights dim, scientists report January 2 at the virtual annual meeting of the Society for Integrative and Comparative Biology.
Bioluminescence is de rigueur in parts of the ocean (SN: 5/19/20). The ability to light the dark has evolved more than 90 times in different species. As a result, the chemical structures that create bioluminescence vary wildly — from single chains of atoms to massive ringed complexes.
With such variability, changes in pH could have unpredictable effects on creatures’ ability to glow (SN: 7/6/10). If fossil fuel emissions continue as they are, average ocean pH is expected to drop from 8.1 to 7.7 by 2100. To find out how bioluminescence might be affected by that decrease, sensory biologist Tom Iwanicki and colleagues at the University of Hawaii at Manoa gathered 49 studies on bioluminescence across nine different phyla. The team then analyzed data from those studies to see how the brightness of the creatures’ bioluminescent compounds varied at pH levels from 8.1 to 7.7.

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As pH drops, the bioluminescent chemicals in some species, such as the sea pansy (Renilla reniformis), increase light production twofold, the data showed. Other compounds, such as those in the sea firefly (Vargula hilgendorfii), have modest increases of only about 20 percent. And some species, like the firefly squid (Watasenia scintillans), actually appear to have a 70 percent decrease in light production.
For the sea firefly — which uses glowing trails to attract mates — a small increase could give it a sexy advantage. But for the firefly squid — which also uses luminescence for communication — low pH and less light might not be a good thing.
Because the work was an analysis of previously published research, “I’m interpreting this as a first step, not a definitive result,” says Karen Chan, a marine biologist at Swarthmore College in Pennsylvania who wasn’t involved in the study. It “provides [a] testable hypothesis that we should … look into.”
The next step is definitely testing, Iwanicki agrees. Most of the analyzed studies took the luminescing chemicals out of an organism to test them. Finding out how the compounds function in creatures in the ocean will be key. “Throughout our oceans, upward of 75 percent of visible critters are capable of bioluminescence,” Iwanicki says. “When we’re wholescale changing the conditions in which they can use that [ability] … that’ll have a world of impacts.” More