Climate

The science is unequivocal: Humans are dramatically overhauling Earth’s climate. The effects of climate change are now found everywhere around the globe and are intensifying rapidly, states a sweeping new analysis released August 9 by the United Nations’ Intergovernmental Panel on Climate Change, or IPCC. And the window to reverse some of these effects is closing.

“There is no room for doubt any longer” about humans’ responsibility for current climate change, says Kim Cobb, a climate scientist at Georgia Tech in Atlanta and an author on the first chapter of the report. “And now we can say quite definitely that a whole class of extreme [events]” is linked to human-caused climate change.

Climate change is already affecting every region on Earth in multiple ways, from drought and fire conditions in the U.S. West to heat waves in Europe and flooding in Asia, the report notes  (SN: 7/7/21). Each of the past four decades has been the warmest on record since preindustrial times (SN: 5/26/21).

The study also looks at several different scenarios of greenhouse gas warming, including perhaps the most hopeful scenarios in which by 2050 the world achieves “net zero” carbon emissions, where emitted gases are balanced by carbon removal from the atmosphere.

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If the world gets down to net-zero emissions, the decades afterward hold “hints of light,” says Baylor Fox-Kemper, an oceanographer at Brown University in Providence, R.I., and the coordinating lead author of the new report’s chapter on oceans and Earth’s icy regions. “Temperatures come back down a little — not all the way back to preindustrial times, but there’s a little recovery.”

But other changes are irreversible on near-future timescales — that is, the next century or more, Fox-Kemper says. Even in those mid-century net-zero emissions scenarios, “it’s still pretty bad,” he says. Sea levels, for example, will continue to rise until about the year 2300, driven in part by the juggernaut of Greenland’s melting ice sheet (SN: 9/30/20). “We may have already crossed [the] threshold beyond which Greenland’s melting could be stopped,” he says. Still, swift and deep emissions reductions would significantly slow how much sea levels will rise by the end of the century, the report finds.

The new analysis is the sixth in a series of massive assessment reports undertaken by the IPCC since 1990. In each report, hundreds of scientists from around the world analyze the findings of thousands of studies to form a consensus picture of how Earth’s climate is changing and what role people play in those changes.

“The key message [of this report] is still the same as was first published in 1990 … human-induced emissions of greenhouse gases pose a threat for humans’ well-being and the biosphere,” said Petteri Taalas, Secretary-General of the World Meteorological Organization, at an event announcing the report’s release August 9.

But researchers understand climate change far better now than they did in 1990, when the first assessment report was released. In the last three decades, new findings have poured in from tens of thousands more observing stations, from a wealth of satellite instruments, and from dramatically improved climate simulations (SN: 1/7/20).

The IPCC’s fifth assessment report, released in several parts during 2013 and 2014, was itself a game changer. It was the first to state that greenhouse gas emissions from human activities are driving climate change — a conclusion that set the stage for 195 nations to agree in Paris in 2015 to curb those emissions (SN: 4/13/14; SN: 12/12/15).

The Paris Agreement set a target of limiting the global average temperature to 2 degrees Celsius above preindustrial times. But many island nations and others most threatened by climate change feared that this target wasn’t stringent enough. So in an unprecedented step, the U.N. commissioned a report by the IPCC to compare how a future Earth might look if warming were limited to just 1.5 degrees Celsius instead.

The Dixie Fire, the largest individual wildfire in California’s history, started on July 13, 2021 and left the town of Greenville, including its library (shown) in ruins. The IPCC’s sixth assessment report finds that humans are unequivocally responsible for the planet’s rising temperatures since the late 1800s, and links these changes to extreme weather including wildfires, drought, heat waves, extreme precipitation and properties of tropical cyclones. Trevor Bexon/Getty Images

That special report, released in 2018, revealed in fine detail how just half a degree of extra warming by 2100 could matter, from the increased likelihood of heat waves to higher sea levels (SN: 12/17/18). The one-two punch of those concrete findings and scorching temperatures in 2019 grabbed the attention of public and policy makers alike.

Scientists were surprised by how hard the 1.5 degree report landed. “Even for me,” says Ko Barrett, vice chair of the IPCC and a senior advisor for climate at the U.S. National Oceanic and Atmospheric Administration, “a person who has dedicated my entire professional career to addressing climate change, the report caused me to rethink my personal contribution to the climate problem. Climate change was not some distant temperature target to be hit in the ethereal future. It was close; it was now.”

IPCC scientists hope the new report, with its powerful emphasis on the regional and local effects of climate change — fully a third of the report is devoted to outlining those — will have a similar impact. And its timing is significant. Beginning October 31, heads of state from around the world are scheduled to meet in Glasgow, Scotland, to discuss updated — and hopefully increasingly ambitious — plans to reduce emissions to meet the targets of the 2015 Paris Agreement. 

With previous reports, “the world listened, but it didn’t hear. Or the world listened, but it didn’t act strongly enough,” said Inger Andersen, executive director of the U.N. Environment Programme, at the Aug. 9 event for the report’s release. “We certainly urge them … to listen to the facts on the table now.” More

The westward journey of the mighty Yukon River takes it from its headwaters in Canada’s British Columbia straight across Alaska. The river has many stories to tell, of generations of Indigenous people hunting on its banks and fishing in its waters, of paddle-wheeled boats and gold panning and pipelines.

Where it meets the Bering Sea, the river fans out into an intricate delta resembling cauliflower lobes of river channels and ponds. The delta has a story to tell, too — that of an increasingly green Arctic.

A composite image of the delta’s northern lobe, taken May 29 by the U.S. Geological Survey’s Landsat 8 satellite, shows willow shrublands lining river channels as they wind toward the sea. Farther inland, tussock grasses carpet the tundra. Grasslike sedge meadows populate low-lying wetlands, punctuated by ponds left behind by springtime floods along the riverbanks from snow and ice that have melted upstream.

In southern Alaska, such as in the Kenai Peninsula, the Arctic has been getting noticeably greener since the 1980s, as global temperatures climb (SN: 4/11/19). Researchers observed this change using satellite measurements of red and near-infrared light reflected off the vegetation. Now, analyses of changing vegetation in the Yukon Delta and nearby Kuskokwim Delta show that more northern areas are getting greener too, researchers report June 1 in Earth Interactions.

The increasing prevalence of tall willows, an important moose habitat, is one sign of these changes in the delta. Moose populations, too, are on the rise. But for the Yukon and other Arctic deltas — where higher floodwaters due to climate change are likely to deposit thicker sediment piles, supporting more greenery — many more changes are likely to come as the planet warms.  More

Climate change is helping Atlantic hurricanes pack more of a punch, making them rainier, intensifying them faster and helping the storms linger longer even after landfall. But a new statistical analysis of historical records and satellite data suggests that there aren’t actually more Atlantic hurricanes now than there were roughly 150 years ago, researchers report July 13 in Nature Communications.

The record-breaking number of Atlantic hurricanes in 2020, a whopping 30 named storms, led to intense speculation over whether and how climate change was involved (SN: 12/21/20). It’s a question that scientists continue to grapple with, says Gabriel Vecchi, a climate scientist at Princeton University. “What is the impact of global warming — past impact and also our future impact — on the number and intensity of hurricanes and tropical storms?”

Satellite records over the last 30 years allow us to say “with little ambiguity how many hurricanes, and how many major hurricanes [Category 3 and above] there were each year,” Vecchi says. Those data clearly show that the number, intensity and speed of intensification of hurricanes has increased over that time span.

But “there are a lot of things that have happened over the last 30 years” that can influence that trend, he adds. “Global warming is one of them.” Decreasing aerosol pollution is another (SN: 11/21/19). The amount of soot and sulfate particles and dust over the Atlantic Ocean was much higher in the mid-20th century than now; by blocking and scattering sunlight, those particles temporarily cooled the planet enough to counteract greenhouse gas warming. That cooling is also thought to have helped temporarily suppress hurricane activity in the Atlantic.  

To get a longer-term perspective on trends in Atlantic storms, Vecchi and colleagues examined a dataset of hurricane observations from the U.S. National Oceanic and Atmospheric Administration that stretches from 1851 to 2019. It includes old-school observations by unlucky souls who directly observed the tempests as well as remote sensing data from the modern satellite era.

How to directly compare those different types of observations to get an accurate trend was a challenge. Satellites, for example, can see every storm, but earlier observations will count only the storms that people directly experienced. So the researchers took a probabilistic approach to fill in likely gaps in the older record, assuming, for example, that modern storm tracks are representative of pre-satellite storm tracks to account for storms that would have stayed out at sea and unseen. The team found no clear increase in the number of storms in the Atlantic over that 168-year time frame. One possible reason for this, the researchers say, is a rebound from the aerosol pollution–induced lull in storms that may be obscuring some of the greenhouse gas signal in the data.  

More surprisingly — even to Vecchi, he says — the data also seem to show no significant increase in hurricane intensity over that time. That’s despite “scientific consistency between theories and models indicating that the typical intensity of hurricanes is more likely to increase as the planet warms,” Vecchi says. But this conclusion is heavily caveated — and the study also doesn’t provide evidence against the hypothesis that global warming “has acted and will act to intensify hurricane activity,” he adds.

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Climate scientists were already familiar with the possibility that storm frequency might not have increased much in the last 150 or so years — or over much longer timescales. The link between number of storms and warming has long been uncertain, as the changing climate also produces complex shifts in atmospheric patterns that could take the hurricane trend in either direction. The Intergovernmental Panel on Climate Change noted in a 2012 report that there is “low confidence” that tropical cyclone activity has increased in the long term.

Geologic evidence of Atlantic storm frequency, which can go back over 1,000 years, also suggests that hurricane frequency does tend to wax and wane every few decades, says Elizabeth Wallace, a paleotempestologist at Rice University in Houston (SN: 10/22/17).

Wallace hunts for hurricane records in deep underwater caverns called blue holes: As a storm passes over an island beach or the barely submerged shallows, winds and waves pick up sand that then can get dumped into these caverns, forming telltale sediment deposits. Her data, she says, also suggest that “the past 150 years hasn’t been exceptional [in storm frequency], compared to the past.”

But, Wallace notes, these deposits don’t reveal anything about whether climate change is producing more intense hurricanes. And modern observational data on changes in hurricane intensity is muddled by its own uncertainties, particularly the fact that the satellite record just isn’t that long. Still, “I liked that the study says it doesn’t necessarily provide evidence against the hypothesis” that higher sea-surface temperatures would increase hurricane intensity by adding more energy to the storm, she says.

Kerry Emanuel, an atmospheric scientist at MIT, says the idea that storm numbers haven’t increased isn’t surprising, given the longstanding uncertainty over how global warming might alter that. But “one reservation I have about the new paper is the implication that no significant trends in Atlantic hurricane metrics [going back to 1851] implies no effect of global warming on these storms,” he says. Looking for such a long-term trend isn’t actually that meaningful, he says, as scientists wouldn’t expect to see any global warming-related hurricane trends become apparent until about the 1970s anyway, as warming has ramped up.

Regardless of whether there are more of these storms, there’s no question that modern hurricanes have become more deadly in many ways, Vecchi says. There’s evidence that global warming has already been increasing the amount of rain from some storms, such as Hurricane Harvey in 2017, which led to widespread, devastating flooding (SN: 9/28/18). And, Vecchi says, “sea level will rise over the coming century … so [increasing] storm surge is one big hazard from hurricanes.” More

Between a death and a burial was hardly the best time to show up in a remote village in Madagascar to make a pitch for forest protection. Bad timing, however, turned out to be the easy problem.

This forest was the first one that botanist Armand Randrianasolo had tried to protect. He’s the first native of Madagascar to become a Ph.D. taxonomist at Missouri Botanical Garden, or MBG, in St. Louis. So he was picked to join a 2002 scouting trip to choose a conservation site.

Other groups had already come into the country and protected swaths of green, focusing on “big forests; big, big, big!” Randrianasolo says. Preferably forests with lots of big-eyed, fluffy lemurs to tug heartstrings elsewhere in the world.

The Missouri group, however, planned to go small and to focus on the island’s plants, legendary among botanists but less likely to be loved as a stuffed cuddly. The team zeroed in on fragments of humid forest that thrive on sand along the eastern coast. “Nobody was working on it,” he says.

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As the people of the Agnalazaha forest were mourning a member of their close-knit community, Randrianasolo decided to pay his respects: “I wanted to show that I’m still Malagasy,” he says. He had grown up in a seaside community to the north.

The village was filling up with visiting relatives and acquaintances, a great chance to talk with many people in the region. The deputy mayor conceded that after a morning visit to the bereaved, Randrianasolo and MBG’s Chris Birkinshaw could speak in the afternoon with anyone wishing to gather at the roofed marketplace.

Courtesy of the staff of the Missouri Botanical Garden, St. Louis and Madagascar

Courtesy of the staff of the Missouri Botanical Garden, St. Louis and Madagascar

Courtesy of the staff of the Missouri Botanical Garden, St. Louis and Madagascar

Conserving natural forests is a double win for trapping carbon and saving rich biodiversity. Forests matter to humans (with a Treculia fruit), Phromnia planthoppers and mouse lemurs.

The two scientists didn’t get the reception they’d hoped for. Their pitch to help the villagers conserve their forest while still serving people’s needs met protests from the crowd: “You’re lying!”

The community was still upset about a different forest that outside conservationists had protected. The villagers had assumed they would still be able to take trees for lumber, harvest their medicinal plants or sell other bits from the forest during cash emergencies. They were wrong. That place was now off-limits. People caught doing any of the normal things a forest community does would be considered poachers. When MBG proposed conserving yet more land, residents weren’t about to get tricked again. “This is the only forest we have left,” they told the scientists.

Finding some way out of such clashes to save existing forests has become crucial for fighting climate change. Between 2001 and 2019, the planet’s forests trapped an estimated 7.6 billion metric tons of carbon dioxide a year, an international team reported in Nature Climate Change in March. That rough accounting suggests trees may capture about one and a half times the annual emissions of the United States, one of the largest global emitters.

Planting trees by the millions and trillions is basking in round-the-world enthusiasm right now. Yet saving the forests we already have ranks higher in priority and in payoff, say a variety of scientists.

How to preserve forests may be a harder question than why. Success takes strong legal protections with full government support. It also takes a village, literally. A forest’s most intimate neighbors must wholeheartedly want it saved, one generation after another. That theme repeats in places as different as rural Madagascar and suburban New Jersey.

Overlooked and underprotected

First a word about trees themselves. Of course, trees capture carbon and fight climate change. But trees are much more than useful wooden objects that happen to be leafy, self-manufacturing and great shade for picnics.

“Plant blindness,” as it has been called, reduces trees and other photosynthetic organisms to background, lamented botanist Sandra Knapp in a 2019 article in the journal Plants, People, Planet. For instance, show people a picture with a squirrel in a forest. They’ll likely say something like “cute squirrel.” Not “nice-size beech tree, and is that a young black oak with a cute squirrel on it?”

This tunnel vision also excludes invertebrates, argues Knapp, of the Natural History Museum in London, complicating efforts to save nature. These half-seen forests, natural plus human-planted, now cover close to a third of the planet’s land, according to the 2020 version of The State of the World’s Forests report from the United Nation’s Food and Agriculture Organization. Yet a calculation based on the report’s numbers says that over the last 10 years, net tree cover vanished at an average rate of about 12,990 hectares — a bit more than the area of San Francisco — every day.

This is an improvement over the previous decades, the report notes. In the 1990s, deforestation, on average, destroyed about 1.75 San Francisco equivalents of forest every day.

Branches of a Dracaena cinnabari dragon’s blood tree from Yemen ooze red sap and repeatedly bifurcate in even Y-splits.BORIS KHVOSTICHENKO/WIKIMEDIA COMMONS (CC BY-SA 4.0)

Trees were the planet’s skyscrapers, many rising to great heights, hundreds of millions of years before humans began piling stone upon stone to build their own. Trees reach their stature by growing and then killing their innermost core of tissue. The still-living outer rim of the tree uses its ever-increasing inner ghost architecture as plumbing pipes that can function as long as several human lifetimes. And tree sex lives, oh my. Plants invented “steamy but not touchy” long before the Victorian novel — much flowering, perfuming and maybe green yearning, all without direct contact of reproductive organs. Just a dusting of pollen wafted on a breeze or delivered by a bee.

To achieve the all-important goal of cutting global emissions, saving the natural forests already in the ground must be a priority, 14 scientists from around the world wrote in the April Global Change Biology. “Protect existing forests first,” coauthor Kate Hardwick of Kew Gardens in London said during a virtual conference on reforestation in February. That priority also gives the planet’s magnificent biodiversity a better chance at surviving. Trees can store a lot of carbon in racing to the sky. And size and age matter because trees add carbon over so much of their architecture, says ecologist David Mildrexler with Eastern Oregon Legacy Lands at the Wallowology Natural History Discovery Center in Joseph. Trees don’t just start new growth at twigs tipped with unfurling baby leaves. Inside the branches, the trunk and big roots, an actively growing sheath surrounds the inner ghost plumbing. Each season, this whole sheath adds a layer of carbon-capturing tissue from root to crown.

“Imagine you’re standing in front of a really big tree — one that’s so big you can’t even wrap your arms all the way around, and you look up the trunk,” Mildrexler says. Compare that sky-touching vision to the area covered in a year’s growth of some sapling, maybe three fingers thick and human height. “The difference is, of course, just huge,” he says.

Big trees may not be common, but they make an outsize difference in trapping carbon, Mildrexler and colleagues have found. In six Pacific Northwest national forests, only about 3 percent of all the trees in the study, including ponderosa pines, western larches and three other major species, reached full-arm-hug size (at least 53.3 centimeters in diameter). Yet this 3 percent of trees stored 42 percent of the aboveground carbon there, the team reported in 2020 in Frontiers in Forests and Global Change. An earlier study, with 48 sites worldwide and more than 5 million tree trunks, found that the largest 1 percent of trees store about 50 percent of the aboveground carbon-filled biomass.

Plant paradise

The island nation of Madagascar was an irresistible place for the Missouri Botanical Garden to start trying to conserve forests. Off the east coast of Africa, the island stretches more than the distance from Savannah, Ga., to Toronto, and holds more than 12,000 named species of trees, other flowering plants and ferns. Madagascar “is absolute nirvana,” says MBG botanist James S. Miller, who has spent decades exploring the island’s flora.

The Ravenala traveler’s tree is widely grown, but native only to Madagascar.CEPHOTO, UWE ARANAS/WIKIMEDIA COMMONS (CC BY-SA 3.0)

Just consider the rarities. Of the eight known species of baobab trees, which raise a fat trunk to a cartoonishly spindly tuft of little branches on top, six are native to Madagascar. Miller considers some 90 percent of the island’s plants as natives unique to the country. “It wrecks you” for botanizing elsewhere, Miller says.

He was rooting for his MBG colleagues Randrianasolo and Birkinshaw in their foray to Madagascar’s Agnalazaha forest. Several months after getting roasted as liars by residents, the two got word that the skeptics had decided to give protection a chance after all.

The Agnalazaha residents wanted to make sure, however, that the Missouri group realized the solemnity of their promise. Randrianasolo had to return to the island for a ceremony of calling the ancestors as witnesses to the new partnership and marking the occasion with the sacrifice of a cow. A pact with generations of deceased residents may be an unusual form of legal involvement, but it carried weight. Randrianasolo bought the cow.

Randrianasolo looked for ways to be helpful. MBG worked on improving the village’s rice yields, and supplied starter batches of vegetable seeds for expanding home gardens. The MBG staff helped the forest residents apply for conservation funds from the Malagasy government. A new tree nursery gave villagers an alternative to cutting timber in the forest. The nursery also meant some jobs for local people, which further improved relationships.

Trying to build trust with people living near southeastern Madagascar’s coast was the first task the Missouri Botanical Garden faced in efforts to conserve the Agnalazaha forest.Courtesy of the staff of the Missouri Botanical Garden, St. Louis and Madagascar

The MBG staff now works with Malagasy communities to preserve forests at 11 sites dotted in various ecosystems in Madagascar. Says Randrianasolo: “You have to be patient.”

Today, 19 years after his first visit among the mourners, Agnalazaha still stands.

Saving forests is not a simple matter of just meeting basic needs of people living nearby, says political scientist Nadia Rabesahala Horning of Middlebury College in Vermont, who published The Politics of Deforestation in Africa in 2018. Her Ph.D. work, starting in the late 1990s, took her to four remote forests in her native Madagascar. The villagers around each forest followed different rules for harvesting timber, finding places to graze livestock and collecting medicinal plants.

Three of the forests shrank, two of them rapidly, over the decade. One, called Analavelona, however, barely showed any change in the aerial views Horning used to look for fraying forests.

Near Madagascar’s Analavelona sacred forest, taxonomist Armand Randrianasolo (blue cap) joins (from left) Miandry Fagnarena, Rehary, and Tefy Andriamihajarivo to collect a surprising new species in the mango family (green leaves at front of image). The Spondias tefyi, named for Tefy and his efforts to protect the island’s biodiversity, is the first wild relative of the popular hog plum found outside of South America or Asia.Courtesy of the staff of the Missouri Botanical Garden, St. Louis and Madagascar

The people living around Analavelona revered it as a sacred place where their ancestors dwelled. Living villagers made offerings before entering, and cut only one kind of tree, which they used for coffins.

Since then, Horning’s research in Tanzania and Uganda has convinced her that forest conservation can happen only under very specific conditions, she says. The local community must be able to trust that the government won’t let some commercial interest or a political heavyweight slip through loopholes to exploit a forest that its everyday neighbors can’t touch. And local people must be able to meet their own needs too, including the spiritual ones.

A different kind of essential

Tied with yarn to nearly 3,000 trees in a Maryland forest, tags displayed the names of the people lost on 9/11. The memorial, organized by ecologist Joan Maloof who runs the Old-Growth Forest Network, helped protect a patch of woods where people could go for solace and meditation.Friends of the Forest, Salisbury

Another constellation of old forests, on the other side of the world, sports some less-than-obvious similarities. Ecologist Joan Maloof launched the Old-Growth Forest Network in 2011 to encourage people to save the remaining scraps of U.S. old-growth forests. Her bold idea: to permanently protect one patch of old forest in each of the more than 2,000 counties in the United States where forests can grow.

She calls for strong legal measures, such as conservation easements that prevent logging, but also recognizes the need to convey the emotional power of communing with nature. One of the early green spots she and colleagues campaigned for was not old growth, but it had become one of the few left unlogged where she lived on Maryland’s Eastern Shore.

She heard about Buddhist monks in Thailand who had ordained trees as monks because loggers revered the monks, so the trees were protected. A month after the 9/11 terrorist attacks, she was inspired to turn the Maryland forest into a place to remember the victims. By putting each victim’s name on a metal tag and tying it to a tree, she and other volunteers created a memorial with close to 3,000 trees. The local planning commission, she suspected, would feel awkward about approving timber cutting from that particular stand. She wasn’t party to their private deliberations, but the forest still stands.

In 1973, high school freshman Doug Hefty wrote more than 80 pages about the value of Saddler’s Woods in Haddon Township, N.J. His typed report, with its handmade cover, played a dramatic role in saving the forest. Saddler’s Woods Conservation Association

As of Earth Day 2021, the network had about 125 forests around the country that should stay forests in perpetuity. Their stories vary widely, but are full of local history and political maneuvering.

 In southern New Jersey, Joshua Saddler, an escaped enslaved man from Maryland, acquired part of a small forest in the mid-1880s and bequeathed it to his wife with the stipulation that it not be logged. His section was logged anyway, and the rest of the original old forest was about to meet the same fate. In 1973, high school student Doug Hefty wrote more than 80 pages on the forest’s value — and delivered it to the developer. In this case, life delivered a genuine Hollywood ending. The developer relented, and scaled back the project, stopping across the street from the woods.

In 1999, however, developers once again eyed the forest, says Janet Goehner-Jacobs, who heads the Saddler’s Woods Conservation Association. It took four years, but now, she and the forests’ other fans have a conservation easement forbidding commercial development or logging, giving the next generation better tools to protect the forest.

Goehner-Jacobs had just moved to the area and fallen in love with that 10-hectare patch of green in the midst of apartment buildings and strip malls. When she first happened upon the forest and found the old-growth section, “I just instinctively knew I was seeing something very different.”

Saddler’s Woods, with a scrap of old-growth forest, has survived in the rush of development in suburban New Jersey thanks to generations of dedicated forest lovers.Saddler’s Woods Conservation Association More

The deadly heat wave that baked the Pacific Northwest in late June would have been “virtually impossible” without human-caused climate change, an international team of scientists announced July 7.

In fact, the temperatures were so extreme — Portland, Ore., reached a staggering 47° Celsius (116° Fahrenheit) on June 29, while Seattle surged to 42° C (108° F) — that initial analyses suggested they were impossible even with climate change, Geert Jan van Oldenborgh, a climate scientist with the Royal Netherlands Meteorological Institute in De Bilt, said at a news conference to announce the team’s findings. “This was an extraordinary event. I don’t know what English word covers it.”

Climate change due to greenhouse gas emissions made the region’s heat wave at least 150 times more likely to occur, the team found. As emissions and global temperatures continue to rise, such extreme heat events could happen in the region as often as every five to 10 years by the end of the century.  

It’s not just that numerous temperature records were broken, van Oldenborgh said. It’s that the observed temperatures were so far outside of historical records, breaking those records by as much as 5 degrees C in many places — and a full month before usual peak temperatures for the region. The observations were also several degrees higher than the upper temperature limits predicted by most climate simulations for the heat waves, even taking global warming into account.

Coming just about a week after the heat wave broke, the new study is the latest real-time climate attribution effort by scientists affiliated with the World Weather Attribution network. Van Oldenborgh and University of Oxford climate scientist Friederike Otto founded the group in 2014 to conduct quick analyses of extreme events such as the 2020 Siberian heat wave (SN: 7/15/20).

In the current study, 27 researchers focused on how the observed temperatures from June 27 to June 29 compared with annual maximum temperatures over the last 50 years for locations across the northwestern United States and southwestern Canada. The team then used 21 different climate simulations of temperatures to analyze the intensity of such a heat wave in the region with and without the influence of greenhouse gas warming.

Earth has already warmed by about 1.2 degrees C relative to preindustrial times. That warming, the researchers determined, increased the intensity of the heat wave by about 2 degrees C. Once global warming increases to 2 degrees C, future heat waves may become even more intense (SN: 12/17/18). Those heat waves could be another 1.3 degrees C hotter, the researchers found.

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That poses a real danger. The late June heat wave took a painful toll (SN: 6/29/21), killing several hundred people — “almost certainly” an underestimate, the researchers say. On June 29, Lytton, a small village in British Columbia, set an all-time Canadian temperature record of 49.6° C (121.3° F). The heat may have exacerbated wildfires that, a day later, swept through British Columbia’s Fraser Canyon region, burning 90 percent of the village, according to local officials. Meanwhile, the U.S. West and southwestern Canada are already bracing for another round of soaring temperatures.

One possible reason for the startling intensity of this heat wave is that, while climate change amped up the temperatures, what happened was still a very rare, unlucky event for the region. How rare isn’t easy to say, given that the observed temperatures were so far off the charts, the researchers say. Under current climate conditions, simulations suggest that such a heat wave might occur once every 1,000 years — but these events will become much more common in future as the climate changes.

By the end of June 2021, more than 40 wildfires burned across Canada’s British Columbia, exacerbated by extreme dryness and the intense heat. One fire burned 90 percent of the town of Lytton, which had set a new temperature record for the country the day before. The fire also generated a massive storm-producing plume of smoke called a pyrocumulonimbus cloud.NASA

Another possibility is grimmer: Climate simulations may not accurately capture what really happens during extreme heat waves. “Climate science has been a bit complacent” about simulating heat waves, assuming that heat wave temperatures would increase linearly along with rising global temperatures, Otto said. But now, Earth’s climate system may have entered a new state in which other climatic factors, such as drier soils or changes to jet stream circulation, are exacerbating the heat in more difficult-to-predict, less linear ways.

The new study didn’t seek to determine which of these possibilities is true, though the team plans to tackle this question over the next few months. However, many scientists have already noted the inability of current climate models to capture what’s really going on.  

“I agree that it is virtually impossible that the [Pacific Northwest] heat wave would have occurred with the observed intensity in the absence of climate change,” Michael Mann, a climate scientist at Penn State who wasn’t involved in the attribution study, commented via e-mail. “But the models used don’t capture the jet stream phenomenon … that WE KNOW played an important role in this event.”

Disproportionate warming of the Arctic region alters temperature gradients high in the atmosphere, which can lead to a wavier jet stream, Mann wrote in the New York Times June 29. That waviness can exacerbate and prolong extreme weather events, such as the heat dome centered over the Pacific Northwest in late June.

This recent heat wave wasn’t just a major disaster, but also posed major scientific questions, van Oldenborgh said. Such an event “would have been judged impossible last year. All of us have just dialed down our certainty of how heat waves behave,” he added. “[We] are much less certain of how the climate affects heat waves than we were two weeks ago.” More

Like a lid on a steaming pot, a high-pressure system is sitting over the U.S. Pacific Northwest and British Columbia, Canada, sending temperatures in the region soaring to unprecedented heights.

From a historic perspective, the event is so rare and extreme as to be a once in a millennium heat wave. But one consequence of Earth’s rapidly changing climate is that such extreme events will become much more common in the region in future, says Larry O’Neill, a climate scientist at Oregon State University in Corvallis.

Temperatures in Portland, Ore., reached 115° Fahrenheit (46° Celsius) on June 29, the highest temperature recorded there since record-keeping began in 1940; average high temperatures for this time of year are about 73° F (23° C). Similar records were notched across the region and more are expected to be set as the high pressure system slowly slides east.

The heat was so extreme it melted transit power cables for Portland’s cable cars and caused asphalt and concrete roads in western Washington to expand and crack. Such high temperatures are particularly dangerous in a normally cool region little used to or prepared for it, raising the risk of heat-related deaths and other health hazards (SN: 4/3/18). Ground-level ozone levels, for instance, also reached the highest seen yet in 2021, the chemical reactions that form the gas amped up by a potent mix of high heat and strong ultraviolet light.

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O’Neill talked to Science News about three things to know about the heat wave.

1. The heat wave is linked to a stalled kink in the jet stream.

Jet streams, fast-moving currents of air high in the troposphere, encircle both poles, helping to push weather systems around Earth’s surface.  The current isn’t smooth and straight; it can meander and form large swirls, peaks and troughs surrounding zones of high- and low-pressure.

Occasionally, these weather patterns stall, becoming stationary “blocking events” that keep a particular spate of weather in place for an extended period of time. One such stalled-out high-pressure zone — basically a large dome of hot, dry weather — is now sitting atop the Pacific Northwest.

The punishing heatwave has an incredible jet stream pattern.The dome of heat will be encircled by the polar jet and this helps lift a sub-tropical jet branch almost into the Canadian Arctic. pic.twitter.com/uIWIIINlSc— Scott Duncan (@ScottDuncanWX) June 25, 2021
London-based meteorologist Scott Duncan tweets about the unusual heat (top) and the jet stream pattern (bottom) that created that heat dome over the Pacific Northwest. In the jet stream image, hot, dry air (in orange) swirls around and maintains a high-pressure system over the region from June 24 to June 29, locking that hot, dry air in place.

Historically, similar high-pressure patterns have brought heat waves to the region, O’Neill says. But this one is different. A typical severe heat wave in the past might lead to temperatures of about 100 °F, he says, “not 115 °F.”

2. Climate change is making the heat wave more severe.

Baseline temperatures were already higher than in the past, due to Earth’s changing climate. Globally, Earth’s average temperatures are increasing, with 2016 and 2020 tied for the hottest years on record (SN: 1/14/21).

Those changes are reflected in what’s now officially considered “normal.” In May, for example, the U.S. National Oceanographic and Atmospheric Administration reported that the country’s new baseline reference temperature, or “climate normal,” will be the period from 1991 to 2020 — also now the hottest 30-year period on record for the country (SN: 5/26/21).

That changing reference makes it tough to place such an unprecedented heat wave in any kind of historical context. “We have a historical data record that’s 100 years long,” O’Neill says. Saying that the heat wave is a once-in-a-millennium event means that “you would expect that, at random chance, this would occur once every 1,000 years. But we’ve never observed this. We have no basis to say this,” he adds. “This is a climate that we’re not accustomed to.”

3. Climate change is likely to make such extreme events more common in the future.

A week before the onset of the heat wave, forecasters were predicting such unprecedented temperatures for the region that many people dismissed those predictions as “being ridiculous,” O’Neill says. “Turns out, [the forecasters] were right.”

Future climate change attribution studies may shed some more light on the ways in which this particular heat wave may be linked to climate change (SN: 7/15/20). Overall, it’s known that climate change is likely to make such extreme events more common in the future, O’Neill says. “We’re seeing these highs form more frequently, and more persistently.” Extreme heat and extreme drought in the U.S. West, for example, can create a reinforcing cycle that exacerbates both (SN: 4/16/20).  

And that poses many dangers for the planet, not least for human health (SN: 4/3/18). In May, scientists reported in Nature Climate Change that 37 percent of heat-related deaths between 1991 and 2018 were attributable to human-caused climate change.  

“When we talk about climate change, often the conversation is a little more abstract,” O’Neill says. “We’re experiencing it right now (SN: 11/25/19). And this question about whether we adapt and mitigate — that’s something we have to figure out right now.” More

When it comes to global warming and sea level rise, scientists have made some dire predictions. One of the most calamitous involves the widespread collapse of ice cliffs along the edges of Greenland and Antarctica, which could raise sea level as much as 4 meters by 2200 (SN: 2/6/19). Now, new simulations suggest that massive glaciers flowing into the sea may not be as vulnerable to such collapses as once believed.

One hypothesis that projected calamitous sea level rise is called the marine ice cliff instability. It suggests that sea-facing bluffs of ice more than 100 meters tall will fail and then slough off to expose fresh ice. Those new cliffs will in turn disintegrate, fall into the sea and float away, setting off a relatively rapid retreat of the glacier that boosts sea level rise.

Although discussed for years, the phenomenon hasn’t yet been seen in today’s glaciers, says Jeremy Bassis, a glaciologist at the University of Michigan in Ann Arbor. “But that may not be surprising, due to the relatively short record of observations in the field and by satellites,” he says.

Because of the dearth of field data, Bassis and colleagues decided to use computer simulations to explore ice-cliff behavior. Unlike previous models, the researchers’ simulations considered how ice flows under pressure as well as how it fractures when highly stressed. This blended model is “a pioneering composite,” says Nicholas Golledge, a glaciologist at the Victoria University of Wellington in New Zealand, who wasn’t involved in the study.

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First, the researchers simulated the collapse of a 135-meter-tall ice cliff on dry land. Over a virtual period of weeks, the face of the cliff shattered and then slumped down to the base, where the icy rubble helped buttress the cliff against further collapse. Researchers have often seen this result in the field, Bassis says.

Then, the team simulated a 400-meter-tall glacier flowing into water that was 290 meters deep. These dimensions are typical of some of the massive glaciers in Greenland flowing into deep fjords, Bassis says. When the cybercliff collapsed, ice that fell into the water at the cliff’s base floated away, leading to repeated failures and rapid, runaway collapse of the glacier. But adding even a small amount of back pressure at the base of the cliff — as would happen if icebergs got stuck and couldn’t waft away, or if they froze in place — prevented a runaway collapse, Bassis and his team reports in the June 18 Science. “We didn’t expect this to be the case,” Bassis says. “But if small bergs got stuck in the shallows ahead of the ice cliff, it was enough to buttress the [cliff] face,” he says.

Simulations of an 800-meter-tall glacier flowing into 690 meters of water, comparable to the dimensions of the Thwaites and Pine Island glaciers in Antarctica, yielded similar results. The researchers also found that in relatively warm ambient temperatures, ice flow upstream of the cliff thins the glacier and reduces the height of the cliff, thus reducing the likelihood of runaway collapses.

The team’s simulations “capture what I think of as realistic behavior,” says Golledge, who coauthored a commentary on the study in the same issue of Science. Future fieldwork may help validate the group’s results. If the simulations hold, Golledge says, the less dire results may mean slower sea level rise in the short term than otherwise predicted.

Bassis and his colleagues’ analysis “is an important piece of work,” says Ted Scambos, a glaciologist at the University of Colorado Boulder, who was not involved in the study. The results, he says, “provide a balance between the possibilities for extreme runaway collapse and some that are more realistic.” More

There’s a new normal for U.S. weather. On May 4, the National Oceanic and Atmospheric Administration announced an official change to its reference values for temperature and precipitation. Instead of using the average values from 1981 to 2010, NOAA’s new “climate normals” will be the averages from 1991 to 2020.

This new period is the warmest on record for the country. Compared with the previous 30-year-span, for example, the average temperature across the contiguous United States rose from 11.6° Celsius (52.8° Fahrenheit) to 11.8° C (53.3° F). Some of the largest increases were in the South and Southwest — and that same region also showed a dramatic decrease in precipitation (SN: 8/17/20).  

The United States and other members of the World Meteorological Organization are required to update their climate normals every 10 years. These data put daily weather events in historical context and also help track changes in drought conditions, energy use and freeze risks for farmers.

That moving window of averages for the United States also tells a stark story about the accelerating pace of climate change. When each 30-year period is compared with the average temperatures from 1901 to 2000, no part of the country is cooler now than it was during the 20th century. And temperatures in large swaths of the country, from the American West to the Northeast, are 1 to 2 degrees Fahrenheit higher. More