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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

If a tree farts in the forest, does it make a sound? No, but it does add a smidge of greenhouse gas to the atmosphere.

Gases released by dead trees — dubbed “tree farts” — account for roughly one-fifth of the greenhouse gases emitted by skeletal, marshy forests along the coast of North Carolina, researchers report online May 10 in Biogeochemistry. While these emissions pale in comparison with other sources, an accurate accounting is necessary to get a full picture of where climate-warming gases come from.

A team of ecologists went sniffing for tree farts in ghost forests, which form when saltwater from rising sea levels poisons a woodland, leaving behind a marsh full of standing dead trees. These phantom ecosystems are expected to expand with climate change, but it’s unclear exactly how they contribute to the world’s carbon budget.

“The emergence of ghost forests is one of the biggest changes happening in response to sea level rise,” says Keryn Gedan, a coastal ecologist at George Washington University in Washington, D.C., who was not involved in the work. “As forests convert to wetlands, we expect over long timescales that’s going to represent a substantial carbon sink,” she says, since wetlands store more carbon than forests. But in the short term, dead trees decay and stop taking up carbon dioxide through photosynthesis, “so that’s going to be a major greenhouse gas source.”

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To better understand how ghost forests pass gas into the atmosphere, the researchers measured greenhouse gases wafting off dead trees and soil in five ghost forests on the Albemarle-Pamlico Peninsula in North Carolina. “It’s kind of eerie” out there, says Melinda Martinez, a wetland ecologist at North Carolina State University in Raleigh.

But Martinez ain’t afraid of no ghost forest. In 2018 and 2019, she measured CO2, methane and nitrous oxide emissions from dead trees using a portable gas analyzer she toted on her back. “I definitely looked like a ghostbuster,” she says.

Wetland ecologist Melinda Martinez totes a portable gas analyzer on her back to measure the “tree farts” emitted by a ghost forest tree. A tube connects the gas analyzer to an airtight seal around the trunk of the tree.M. Ardón

Soils gave off most of the greenhouse gases from the ghost forests. Each square meter of ground emitted an average 416 milligrams of CO2, 5.9 milligrams of methane and 0.1 milligrams of nitrous oxide per hour. On average, dead trees released about 116 milligrams of CO2, 0.3 milligrams of methane and 0.04 milligrams of nitrous oxide per square meter per hour — totaling about one-fourth the soil’s emissions.

Measuring greenhouse gases from the trees is “kind of measuring the last breath of these forests,” says Marcelo Ardón, an ecosystems ecologist and biogeochemist at North Carolina State University. The dead trees “don’t emit a ton, but they are important” to a ghost forest’s overall emissions.

Ardón coined the term “tree farts” to describe the dead trees’ greenhouse gas emissions. “I have an 8-year-old and an 11-year-old, and fart jokes are what we talk about,” he explains. But the analogy has a biological basis, too. Actual farts are caused by microbes in the body; the greenhouse gases emitted by ghost forests are created by microbes in the soil and trees.

In the grand scheme of carbon emissions, ghost forests’ role may be minor. Tree farts, for instance, have nothing on cow burps (SN: 11/18/15). A single dairy cow can emit up to 27 grams of methane — a far more potent greenhouse gas than CO2 — per hour. But accounting for even minor sources of carbon is important for fine-tuning our understanding of the global carbon budget, says Martinez (SN: 10/1/19). So it would behoove scientists not to turn up their noses at ghost tree farts.   More