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By Michael Allen

Last year was hot. NASA declared that it tied 2016 for the hottest year on record, and the Met Office of the United Kingdom said it was the final year in the warmest 10-year period ever recorded. Temperatures were particularly high in Siberia, with some areas experiencing monthly averages more than 10°C above the 1981–2010 average. Overall, Siberia had the warmest January to June since records began; on 20 June, the town of Verkhoyansk, Russia, hit 38°C, the highest temperature ever recorded in the Arctic Circle.

In a new article in Climatic Change, Andrew Ciavarella from the Met Office and an international team of climate scientists showed that the prolonged heat in Siberia would have been almost impossible without human-induced climate change. Global warming made the heat wave at least 600 times more likely than in 1900, they found.

Ciavarella said that without climate change, such an event would occur less than once in thousands of years, "whereas it has come all the way up in probability to being a one in a 130-year event in the current climate." Ciavarella and his coauthors are part of the World Weather Attribution initiative, an effort to "analyze and communicate the possible influence of climate change on extreme weather events."

According to the Met Office, events leading to Siberia's prolonged heat began the previous autumn. Late in 2019, the Indian Ocean Dipole—the difference in sea surface temperature between the western and eastern Indian Ocean—hit a record high, supercharging the jet stream and leading to low pressure and extreme late winter warmth over Eurasia. This unseasonably warm weather persisted into spring and reduced ice and snow cover, which exacerbated the warm conditions by increasing the amount of solar energy absorbed by land and sea.

Cataloging the Past, Forecasting the Future

The resulting high temperatures unleashed a range of disasters. Most obvious were wildfires that burned almost 255,000 square kilometers of Siberian forests, leading to the release of 56 megatons of carbon dioxide in June. The heat also drove plagues of tree-eating moths and caused permafrost thaws that were blamed for infrastructure collapses and fuel spills, including one leak of 150,000 barrels of diesel.

The researchers compared the climate with and without global warming using long series of observational data sets and climate simulations. At the beginning of the 20th century, similar extremely warm periods in Siberia would have been at least 2°C cooler, they found. Global warming also made the record-breaking June temperature in Verkhoyansk much more likely, with maximum temperatures at least 1°C warmer than they would have been in 1900.

The team also looked to the future. They found that by 2050 such warm spells could be 2.5°C to 7°C hotter than in 1900 and 0.5°C to 5°C warmer than in 2020. "Events of precisely the magnitude that we saw, they will increase in frequency, and it wouldn't be unexpected that you would then see also events of an even higher magnitude as well," Ciavarella said.

Dim Coumou, a climate scientist at Vrije Universiteit Amsterdam, agrees that such an event would not have happened in a preindustrial climate. "With global warming summer temperatures are getting warmer, and therefore, the probability of heat waves and prolonged warm periods are really strongly increasing," he explained, adding that this pattern is particularly pronounced in Siberia, as the high latitudes are warming faster. Coumou was not involved in the new research.

In addition to local issues (like the health impact of heat exposure, wildfires, and the collapsing of structures built on thawing permafrost), we should also be concerned about the wider impact of heat events in Siberia, said Martin Stendel, a climate scientist at the Danish Meteorological Institute. Stendel was not involved in the new research but has worked on other studies for World Weather Attribution. Thawing permafrost, for example, releases greenhouse gases such as carbon dioxide and methane into the atmosphere.

"We should be aware that things may have global effects," he said.

This story originally appeared in Eos and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.

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dottedhippo / iStock / Getty Images Plus

By Kimberly M. S. Cartier

As the Arctic continues to warm, climate changes cascade into the marine environment. Top predators like polar bears, beluga whales, and narwhals are affected by shifting seasonality and loss of the Arctic sea ice that shapes where they live and what they eat. Moreover, changes in ocean currents alter the transport of toxins like mercury through Arctic waters, which can create health concerns for top consumers in marine food webs.

Historically, it has been difficult to track how decades of changes in the marine environment have impacted the denizens of the Arctic deep. A recent Current Biology study has shown, however, that the iconic spiral tusks of male narwhals record chemical tracers of diet and mercury exposure over the animals' lifetimes and provide a new paleorecord of the Arctic.

"The tusk is a relatively rare sample to get a hold of … but what's unique about them that is we can do a time trend analysis for each individual," which hasn't been possible before, said Jean-Pierre Desforges, a postdoctoral fellow in marine mammal toxicology at McGill University in Montreal who coauthored the new study. "We don't have that many tusks, but for each tusk we have a lot of data points."

A Change in Diet

Narwhals spend months at a time under Arctic sea ice in remote areas of the world, which can make sample collection very challenging. To date, most data on the impacts of climate change on narwhal come from tissue sampling, which can provide a brief snapshot of an animal's environment. If a researcher wanted to understand these impacts over a narwhal's 50-year life, they'd have to collect tissue samples for 50 years. This limits analysis of trends across a narwhal's lifetime — the samples might come from many animals, or different collection methods might be used. In population-level studies, trends can be overwhelmed by variations among individual animals.

Narwhal tusks provide an alternative. A tusk is an enlarged canine tooth that grows a little bit each year and is connected to the animal's circulatory system. Like whale earplugs, baleen, hair, and teeth, narwhal tusks can be a valuable archive of the animal's environment and habits. A single tusk provides decades' worth of data for a single narwhal. "From the time the animal was killed, we can backtrack through the animal's whole lifetime," Desforges said.

Carbon and nitrogen stable isotopes in the layers of a male narwhal's tusk track whether the animal's food source is from sea ice–dominated waters or open ocean. Rune Dietz

Desforges and his colleagues collected 10 narwhal tusks, each about 1–2.5 meters in length, from animals who lived in the waters off northern Greenland. The team measured stable isotopes of carbon and nitrogen — δ13C and δ15N — as well as mercury levels at multiple points along the length of each tusk, representing growth from 1962 to 2010.

"The carbon isotopes are pretty good trackers of habitat use," Desforges said. "The signals of carbon are very different if you're feeding nearshore or offshore like deep in the ocean, if you're feeding along the sediment at the bottom of the ocean or within the water column…and if you're feeding along the ice-associated food web." Nitrogen isotopes track where on a food web an animal is eating. By combining information from the two isotope signals the team was able to decipher broad trends in the narwhals' diets over their lifetimes.

The tusks revealed that before 1990, the narwhals' diet primarily came from sympagic food webs associated with sea ice, with fish like halibut and Arctic cod. After 1990, narwhals primarily ate open-water (pelagic) food like capelin and armhook squid. This pattern broadly matches observed changes in Arctic sea ice and marine habitats during the study period: Climate-driven changes in the ocean have pushed more pelagic fish into icy Arctic waters, and with less sea ice, narwhals have had to shift where they hunt to better avoid predators like orcas.

Mercury Marks Human Impact

As with δ15N, mercury levels track food web position. In the tusk samples, mercury levels rose with an animal's age and declined as its food source shifted from sympagic prey, which are often at higher trophic levels and have greater bioaccumulation and biomagnification of toxins, to pelagic prey. Temporal trends in the tusks' mercury and nitrogen matched up until 2000, when they sharply diverged.

"The diet suggests that mercury should be going down, whereas the mercury levels rise," Desforges said. "Not only that, they rise a lot faster than they had in the previous decades. So the diet is not the major driver of mercury in recent decades. We propose that [the increase in mercury is associated with] increased global emissions of mercury or else a climate change impact where mercury is becoming more available in the Arctic."

Analyzing more tusks collected in Greenland and elsewhere could help scientists trace where the mercury is coming from and better understand the potential health impacts of mercury on Arctic marine mammals.

Narwhal tusk expert Martin Nweeia, a dental researcher at Case Western Reserve University in Cleveland, Ohio, and Harvard University in Cambridge, Mass., told Nunatsiaq News that insights from tusk samples should be seen as one piece of the puzzle in tracking environmental change. Nweeia, who was not involved with this study, agrees with the researchers that tissue samples and actual stomach contents of tusked and nontusked males and females are needed to see the whole picture. He added that the best way forward would be to work with Inuit and let traditional knowledge guide that work. "I'd be curious what hunters think because they're cutting open stomachs all the time," he said. "They know exactly what that diet is."

The tusks used in this study were provided by Avanersuaq and Uummannaq hunters after traditional subsistence hunts, but "we probably have tusks in museums around the world dating back to who knows when," Desforges noted. "We can get really valuable information if the tusks are in good shape and preserved in the right way. Samples go back in time before the Industrial Revolution, so we could get a good idea of what the prehuman baseline would be for mercury in marine mammals."

This story originally appeared in Eos and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.

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By Hannah Thomasy

From 2014 to 2016, the Gulf of Alaska experienced the worst marine heat wave of the decade. From single-celled organisms to top predators, practically no level of the ecosystem was left unscathed. During the Pacific marine heat wave, tens of thousands of dead seabirds washed up on beaches, unusually low numbers of humpback whales arrived in their summer habitats, and toxic algal blooms spread along the West Coast of North America.

Now, a new study in Scientific Reports casts doubt on whether Gulf ecosystems will be able to return to their pre–heat wave conditions. This study—a collaborative effort between researchers at NOAA and several other government and research organizations—combined dozens of data sets to build a detailed picture of how many heat wave–induced changes have persisted. Thanks in part to long-term monitoring efforts by Gulf Watch Alaska, a program established in 2012 to assess the ongoing effects from the 1989 Exxon Valdez oil spill, scientists were able to compare pre–heat wave and present conditions in several different sections of the ecosystem.

"We were able to show these impacts—from the intertidal out to the pelagic [open ocean] ecosystem, and from algae and phytoplankton on up to whales and commercial fisheries, and a lot of different species in between," said Robert Suryan, a NOAA marine biologist and lead author of the study.

Shannon Atkinson, a professor in the College of Fisheries and Ocean Sciences at the University of Alaska Fairbanks who was not involved in this study, said it's very important that we understand the changes taking place in the Gulf of Alaska. "The ecological significance is huge," she said. "We've seen such dramatic changes in the Far North…it really has made Alaska like a ground zero for climate change."

In addition to impacts on the animals that make their homes in the Gulf of Alaska, changes in the Gulf ecosystem could have major implications for the livelihoods of many Alaskans as well. This region supports subsistence fisheries, commercial fisheries, and a major tourism industry.

Changing Ecosystems

For some animals, the heat wave was devastating. Most metrics showed a decline in sea stars, herring, and Pacific cod; their populations today generally remain lower than pre–heat wave measures. Numbers of sea lion pups trended downward, and some areas had fewer nesting seabirds like common murres and kittiwakes.

But, Suryan pointed out, as some species suffered, others thrived. For example, researchers saw a major decrease in the amount of brown algae in the intertidal zone. That's bad news for species like herring, which lay their eggs on the algae. But as algae cover decreased, "that opened up space" for other organisms in the intertidal zone, explained Suryan. "In tidal communities, there's a lot of competition for space, so there was an increase in barnacles and mussels.… So that's a benefit to communities that rely more on those particular species."

Similarly, there have been positive and negative effects on different fisheries in the region. Although the Pacific cod fishery has suffered in the years during and since the heat wave, Suryan said that juvenile sablefish have been surviving and growing at greater rates than usual, so sablefish fisheries will likely do well in the coming years.

As ecosystems change, we as humans need to change how we interact with and manage them, researchers said. "With these types of studies, we're hopeful that we can really benefit the management of natural resources," said Suryan. "[We're] thinking about the communities in the region and the industries in the region—how can we help inform their adaptation to this change?"

An Uncertain Future

This study is just the beginning. Suryan looks forward to more focused research on the mechanisms by which these changes are occurring. Why do some species do better than others? Even within the same species, why do some age groups thrive while others decline? By understanding such mechanisms, he said, we will be better able to predict how the changing climate will affect the future of these important ecosystems.

In addition to measuring the number of animals in the population, Atkinson said that measuring things like reproductive rates and biomarkers of stress can also be valuable indicators of how well a group of animals is faring in a changing environment.

Unfortunately, climate change may not be the only threat these animals face. Atkinson said it's important to determine how animals will respond to cumulative stressors (including climate change, disease, and pollution) to predict how well populations will survive in the coming years.

This story originally appeared in Eos and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.

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