A drunken forest in Alaska, where trees are tilting or collapsing to the ground due to permafrost melt
Global Warming Images/Shutterstock
Melting permafrost in Arctic forests may cause trees to tilt to the side in ways that slow their growth, reducing the amount of carbon these “drunken forests” store.
The northern hemisphere’s boreal forest is a vast ecosystem that contains up to 40 per cent of all carbon stored on land. Rapid warming of the Arctic due to climate change is already affecting how these forests grow and thus how much carbon they store. It is also melting…
A destructive 2022 storm in Spain produced large hailstones up to 12 centimetres in diameter
Tomeu Rigo Ribas
A scanner at a dentist’s office has produced the first high-resolution 3D images of the internal structure of large hailstones. Such detailed views could help researchers better forecast which storms will generate these destructive pieces of ice.
“The first result was impressive,” says Carme Farnell Barqué at the Meteorological Service of Catalonia in Spain. “Wow! We can see the interior of the stone without breaking it. We could see different layers, with different densities.”
The hailstones fell during an intense storm that struck the northeast of Spain in 2022, killing one child, injuring dozens of people and causing millions of dollars’ worth of damage. The largest hailstones that fell had diameters of 12 centimetres, about twice the size of a tennis ball.
A few days after the storm, Farnell Barqué and her colleagues asked around to see if anyone had kept any of the hail. They collected 14 hailstones, up to 8.5 centimetres in diameter, that people had stored in plastic bags in their freezers.
Hailstones form when layers of supercooled water accumulate on an initial embryonic ice particle in a storm. The shape and density of these layers of ice within hailstones can reveal details about the growth process. But normally, researchers can only study a few cross-sections of a single hailstone by slicing open the ice with a hot knife.
In this case, an orthodontist friend of Farnell Barqué suggested the researchers instead use a CT scanner to reveal the hailstones’ complete internal structure. And a scanner was available in a dentist’s office.
The team scanned three of the hailstones, generating hundreds of cross-sections showing variations in density within each piece of ice. Some of the details were surprising: for instance, although the hailstones were spherical, their nuclei were located far off centre. Farnell Barqué says this suggests the thickest part of the stone formed as it was falling, rather than when it was cycling between different altitudes on updrafts within the storm.
Julian Brimelow at the Northern Hail Project in Canada says a few other small hailstones have been scanned this way, but the stones from Spain are much larger. “This is important, because we are still not certain how and where in a thunderstorm hail grows to achieve such impressive sizes,” he says.
This better understanding could improve forecasts of hail size in future storms. “We can associate each layer of the growing part with the radar data on the evolution of the thunderstorm,” says Tomeu Rigo at the Meteorological Service of Catalonia. “Then it’s possible to relate this with new thunderstorms and project our results to the future.”
“We probably do need to look at this for more hailstones,” says John Allen at Central Michigan University, who is planning a large hailstone-collecting survey in the US Great Plains in 2025. “The question is: how viable is this method for large numbers of stones?”
Drilling for ice cores helps reveal the health of the Antarctic
Nerilie Abram
If all our fear and uncertainty over climate change could be distilled into a single statistic, then arguably it was delivered to an emergency summit on the future of the Antarctic last month.
Nerilie Abram at the Australian National University, Canberra, opened her presentation with a slide headlined “Antarctic sea ice has declined precipitously since 2014, and in July 2023 exceeded a minus 7 sigma event”.
Around 1.1 billion people live around lakes that freeze
mktotoro/iStockphoto/Getty Images
Like melting sea ice and glaciers, the frozen sheets that cover lakes are vanishing, too. Lake ice loss has accelerated over the past 25 years, with lakes in the northern hemisphere melting an average of 45 days earlier than they did a century ago.
“The loss of ice in freshwater systems has consequences that are social, environmental and economic,” says Stephanie Hampton of the Carnegie Institution for Science in Washington DC.
Slowly cracking through the dense pack ice of Antarctica’s Weddell Sea is hefty, ice-breaking research vessel S. A. Agulhas II (pictured below). It was part of Endurance22, a successful 2022 expedition to locate the sunken ship of explorer Ernest Shackleton.
James Blake/Falklands Maritime Heritage Trust
Endurance went down in 1915 after it was trapped by pack ice during its first voyage – leaving him and his crew of 27 men stranded, with little hope of rescue. “The story of survival of Shackleton and the crew of the Endurance is a legendary feat of leadership, grit, determination and perseverance against all the odds,” says Nico Vincent, deputy leader of the Endurance22 expedition. In new book Endurance, he and the wreck mission leader John Shears detail the search for the lost ship.
James Blake/Falklands Maritime Heritage Trust
A stunning bird’s-eye view (pictured above) shows members of Endurance22’s subsea team edging a returning underwater autonomous vehicle into position at the vessel’s stern before heaving it onboard again.
James Blake/Falklands Maritime Heritage Trust
But, fittingly, centre stage (above) is taken by an amazing mosaic of over 25,000 images of the wreck itself. It reveals an incredibly well-preserved ship, its masts, anchors and steam engine funnel all still present, while the hull is also intact, resting upright on the seabed. Shears and Vincent hope the story of the ship will offer a fresh perspective on the epic tale for a new generation.
Endurance: The discovery of Shackleton’s legendary ship by John Shears and Nico Vincent is published on 5 November
For the second year in a row, Antarctic sea ice has reached near-record low levels. This reinforces concerns that human-caused climate change has initiated a lasting “regime shift” in the amount of ice that forms in the Southern Ocean each year.
“Last year we were talking about whether Antarctic sea ice is undergoing a regime shift. Not anymore,” says Edward Doddridge at the Institute for Marine and Antarctic Studies in Australia. “Antarctica has pretty definitively answered that question for us. Now we are talking about what the impacts of that…
Sergio Pitamitz/VW Pics/Universal Images Group via Getty Images
Rising land beneath Antarctica’s ice sheet could slow ice loss and reduce sea-level rise in coming centuries. However, if emissions continue to rise, the effect could raise sea levels even more than the melting ice alone.
The finding comes from a model that simulates the mantle – the layer beneath Earth’s crust – in more detail than ever before. As melting ice reduces the weight of Antarctica, the elastic mantle below rebounds, raising the land above it. As melting ice reduces the weight of the continent, Earth’s elastic mantle rebounds, raising the land above it. The rebounding land may in turn slow the flow of the ice sheet where it meets the sea. This “sea level feedback” mainly happens because the rising land reshapes the seabed in a way that limits the thickness of the ice sheet at its edge – thinner ice there reduces the overall flux of ice into the sea.
Researchers have long thought this effect would play some role in slowing ice loss. But it wasn’t clear when this effect would kick in, or how it would vary at different parts of the ice sheet.
Natalya Gomez at McGill University in Canada and her colleagues modelled the relationship between the melting ice and rebounding land, including a simulation of the mantle that captured differences in viscosity beneath the continent. East Antarctica sits above a more viscous mantle and thicker crust, while West Antarctica’s rapidly melting glaciers lie atop a less viscous mantle and thinner crust. This more detailed picture of the interior Earth is based on decades of precise measurements of changes in the elevation of the ice sheet, as well as data about the mantle below Antarctica from seismic waves produced by earthquakes. “This is something that’s been hard earned,” says Gomez.
Under a very low-emissions scenario, the researchers found rebounding land reduced Antarctica’s contribution to global average sea level rise by over half a metre by 2500, compared with a model that treated the ground beneath the ice as rigid. This effect was less significant under a moderate emissions scenario, but it still led to a substantial reduction in sea level rise, which kicked in as soon as 2100.
However, under a very high emissions scenario, the team found that rebounding land led Antarctica to contribute an additional 0.8 metres to sea level rise by 2500. This happened because the ice sheet receded faster than the land rebounded, and because the rising seafloor displaced more water into the rest of the ocean.
“From a modelling perspective it’s a very big advance,” says Alexander Bradley at the British Antarctic Survey. He says rebounding land was always assumed to reduce sea level rise, but this higher-resolution modelling shows that the effect depends on emissions. “The changes that take place in the 21st and 22nd century are really baked in by what we do now,” says Bradley.
Alexander Robel at the Georgia Institute of Technology in Atlanta says “it’s a very good simulation”, but the scenario where rebounding land increases sea level rise is based on worst-case assumptions about emissions as well as the rate at which the ice sheet retreats.
Queshque glacier in Peru is retreating because of global heating
Emilio Mateo/Aspen Global Change Institute
Mountain glaciers in the Andes are almost certainly the smallest they have been for at least 130,000 years, a study of rocks exposed by the melting ice has found.
“This shocked us, frankly,” says Andrew Gorin at the University of California, Berkeley. “I think this is clear evidence that at least one region in the world has now departed the hospitable climatic conditions that have fostered the development of human civilisation.”
The Andes mountain range is so high up that there are permanent glaciers in many places, even in tropical areas. In fact, almost all of the world’s tropical glaciers are in the Andes.
It has been clear for decades that these glaciers are both thinning and retreating as a result of global heating. But how this compares with what happened in the more distant past hasn’t been clear.
Gorin and his colleagues have analysed 20 samples of rock that were recently exposed due to the retreat of four tropical glaciers in the Andes. They looked for isotopes of carbon and beryllium that form when exposed rock is hit by cosmic rays, which can reveal when a glacier last retreated past a certain point.
Similar studies in northerly regions of the world have shown that glaciers there were at their smallest a few thousand years ago, around the middle of the current interglacial period. This is because changes in Earth’s orbit resulted in northern areas getting more winter sunshine, says Gorin, causing glaciers to retreat.
While the shrinking of northern glaciers in the mid-interglacial was a regional rather than global phenomenon, the researchers expected to find something similar in the Andes at that time. Instead, levels of the isotypes they found were so low that they were almost undetectable.
“This is an alarm bell. It’s the canary in the coal mine for mountain glaciers everywhere,” says Gorin.
“We’re quickly blowing past climate milestones that we thought were decades away,” he says. “We chose the specific locations that we sampled at these glaciers with the implicit assumption that these glaciers were not smaller than they have ever been in human history.”
The findings show directly that these glaciers didn’t retreat as far as they have today at any time in the past 11,700 years. Before this point, there was a global glacial period, and studies by other teams show that the tropics were cooler then.
While the study doesn’t say this, Gorin agreed when asked that this means Andean glaciers have almost certainly shrunk to the smallest they have been since at least the previous interglacial, around 130,000 years ago.
“I’d bet my life savings that your assertion that these glaciers are now the smallest they’ve been since the last interglacial is true,” he says. “However, due to the limitations of the technique we used to address this question, we can’t definitively prove that fact, and this is why we don’t say so in the article.”
“This is a shocking piece of research,” says Liam Taylor at the University of Leeds in the UK. “Undoubtedly, the science is conclusively showing that glaciers across the Andes are in a state that they haven’t been in since before the Holocene began 11,700 years ago, and this is directly caused by human activities changing the climate.”
The retreat of glaciers is already affecting farming, drinking water supplies, sanitation and hydropower in the region, says Taylor. This is because glaciers act as reservoirs, storing winter snowfall and releasing meltwater in the summer.
“Many of the glaciers in this region have now passed ‘peak water’, meaning that meltwater that supplies freshwater downstream is drying up,” he says.
In the past century, tens of thousands of people in Peru have also been killed by floods caused by the bursting of lakes formed as the glaciers retreated, says Stephan Harrison at the University of Exeter in the UK. More such disasters could occur around the world as mountain glaciers retreat.
Climate models suggest that mountain glaciers will lose more than 90 per cent of their ice by the end of the century, he says, leaving just a few small glaciers in the highest areas.
It was 21 years ago that I trekked and swam solo, without resupply, across the icy Arctic Ocean from Canada to the North Geographic Pole. The feat hasn’t yet been repeated and probably won’t be due to a drop in sea-ice cover caused by warming resulting from greenhouse gas emissions far to the south.
It had taken three attempts over 15 years before success in 2003 in reaching the pole, around 770 kilometres from Canada in the central Arctic Ocean’s “high seas”. By then, the nature of the 75-day challenge had morphed to require an amphibious element – swimming between…
Broken sea ice in Lancaster Sound, part of the Northwest Passage
Alison Cook
Shipping companies have anticipated that melting sea ice will open a shorter route through the Canadian Arctic, but they may see their hopes dashed by thicker ice flowing in from further north.
“The northern part [of the Northwest Passage] is not going to be an open new shipping route anytime soon,” says Alison Cook at the Scottish Association for Marine Science.
For more than a century, sailors have navigated the icy waters of the Canadian Arctic along the Northwest Passage, which has offered a treacherous but efficient route between the Atlantic and Pacific Oceans. Melting sea ice due to climate change has made the southern part of the passage less risky, and voyages through it have quadrupled since 1990.
The northern part of the passage promises an even shorter route, but few ships use it because it remains bound with ice for more of the year than the southern part does. However, the entire passage had a nearly ice-free summer in 2007, and additional warming has occurred since, leading many to assume the northern part of the route is on track to become routinely navigable. That possibility has spurred visions of an Arctic shipping boom.
Cook and her colleagues used ice charts that the Canadian government supplied to sea captains between 2007 and 2021 to assess whether such visions were coming true. For each section of the Northwest Passage, they determined the number of weeks per year with little-enough ice that it would be safe for a moderately ice-worthy vessel to sail through.
Map showing the routes that can be taken through the Northwest Passage in the Canadian Arctic Archipelago
Alison Cook
This detailed view of the ice revealed that, rather than an opening of the passage, the safe shipping season declined along several “choke points” during that period, especially on the northern route. The shipping season in the east of the Beaufort Sea fell from 27 weeks to 13 weeks, for instance. The M’Clure Strait season declined from 6.5 weeks to just 2 weeks of safe shipping per year. Other areas saw seasons extend by a few weeks or experienced no change, but the openness of the overall route is set by the section with the shortest season, says Cook.
The researchers attribute the shorter seasons mainly to an increase in thicker sea ice flowing in from the region north of Greenland known as the Last Ice Area. As the climate warms, this site is expected to be the final redoubt for Arctic sea ice. “It’s becoming a bit less robust because of climate change, and it’s becoming more mobile,” says Cook.
The finding matches expectations that ice will survive longest in the Canadian Arctic, says Amanda Lynch at Brown University in Rhode Island, who wasn’t involved with the research. A bigger geopolitical and economic question now is how melting ice will affect shipping on the Russian side of the Arctic, she says.
