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

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

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

The COVID-19 pandemic wasn’t just a shock to the human immune system. It was also a shock to the Earth system, dramatically changing the air quality in cities around the globe.
As countries around the globe struggled to contain the disease, they imposed temporary shutdowns. Scientists are now sifting through data collected by satellite and on the ground to understand what this hiatus in human activities can tell us about the atmospheric cocktail that generates city pollution. Much of this preliminary data was shared at the American Geophysical Union annual meeting in December.
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It was already known that peoples’ activities were curtailed enough to result in a dramatic drop in emissions of greenhouse gases in April, as well as a dip in the seismic noises produced by humans (SN: 5/19/20; SN: 7/23/20). That quiet period didn’t last, though, and carbon dioxide emissions began to climb back upward by the summer. April 2020 saw a drop of about 17 percent in global monthly CO2 emissions from fossil fuels, but by year’s end, annual CO2 emissions for the globe were only 7 percent lower than they were in 2019. That reduction was too brief, compared with the hundreds of years that the gas can linger in Earth’s atmosphere, to put a dent in the planet’s atmospheric CO2 level (SN: 8/7/20).

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But in addition to briefly reducing emissions of climate-warming gases, this abrupt halt in many human activities — particularly commuter traffic — also created an unprecedented experiment for scientists to examine the complicated chemistry of atmospheric pollutants in cities. By altering the usual mix of pollutants hovering over cities, the shutdowns may help scientists better understand another longstanding misery for human health: poor air quality in many cities.
That’s not to say that the pandemic has a silver lining, says Jessica Gilman, a tropospheric chemist at the National Oceanic and Atmospheric Administration in Boulder, Colo. “Misery is no solution to our global environmental challenges.”
But there’s now a wealth of data from cities around the globe on how the pandemic altered regional or local concentrations of the precursors of ozone, a primary component of smog. Those precursors include nitrogen oxides and volatile organic compounds — both produced by traffic — as well as methane, produced by the oil and gas industry. With satellites, scientists are also able to assess how levels of these pollutants changed around the globe.
Building a global picture of altered city pollution is no easy task, though. Researchers are finding that the pandemic’s impact on levels of various pollutants was highly regional, affected by differences in wind and rain as well as by photochemical interactions with sunlight — the intensity of which also changes with the season.  
That stark variety of regional effects was evident in, for example, the different post-pandemic ozone levels in Denver and New York City. Nitrogen oxide gases produced by traffic are a powerful precursor to cities’ elevated ozone levels, which can damage the lungs and trigger respiratory ailments. The United States has made strides in reducing these gases over the last few decades — but there hasn’t been a corresponding drop in ozone levels, Dan Jaffe, an environmental chemist at the University of Washington Bothell, reported at the meeting on December 9.
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The shutdowns gave researchers some insight into why, Jaffe says. From March 15 through July 23, New York City had a 21 percent decrease in nitrogen dioxide, one of several nitrogen oxide gases, in comparison with 2019 levels. Although the shutdowns were more stringent during the spring months, it turned out that summertime reductions in nitrogen dioxide were most strongly linked to the city’s change in ozone levels, the researchers found. “We see very strong reduction in summertime ozone this year,” Jaffe said at the meeting, citing unpublished data.
That’s because in the summer months, heat and sunlight react with the precursor gases in the atmosphere, like nitrogen dioxide, creating a toxic cocktail. This kind of insight can be a boon to policy makers in a non-pandemic year, suggesting that nitrogen oxide regulations should focus most strongly on the summer, Jaffe says. “It’s really good evidence that NOx reductions extending into July in 2020 had an important impact.”
In Denver, however, ozone didn’t drop so consistently — possibly because wildfires were beginning to rage across the U.S. West by the end of the summer (SN: 12/21/20). The fires produce nitrogen oxides, carbon monoxide and fine particles that can also help to increase ground-level ozone.
“There are different patterns in different cities,” Jaffe says. “There are a lot of factors to sort out, and a lot of work to be done.” Armed with a wealth of new data from 2020, scientists hope to be able to make some headway. More

2020 was a year of unremitting extreme climate events, from heat waves to wildfires to hurricanes, many of which scientists have directly linked to human-caused climate change (SN: 8/27/20). Each event has taken a huge toll in lives lost and damages incurred. As of early October, the United States alone had weathered at least 16 climate- or weather-related disasters each costing more than $1 billion. The price tags of the late-season hurricanes Delta, Zeta and Eta could push the final 2020 tally of such expensive disasters even higher, setting a new record.
With the COVID-19 pandemic dominating the news, some of these events may have already faded into memory. Here, Science News takes a look at this year of climate extremes.

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Australia’s ‘black summer’
The bushfires that burned southeastern Australia between July 2019 and March 2020 scorched roughly 11 million hectares and killed dozens of people. Climate change made those devastating fires at least 30 percent more likely to occur, researchers reported (SN: 3/4/20). The primary reason: a prolonged and severe heat wave that baked the country in 2019 and 2020, which itself was exacerbated by climate change.
The intensity of Australia’s fires produced some striking sights. A particularly intense fire led to the formation of towering pyrocumulonimbus clouds that launched hundreds of thousands of metric tons of smoke into the stratosphere (SN: 6/15/20).
One massive plume of smoke, wrapped in rotating winds, ascended to a record 31 kilometers in the atmosphere, deep into Earth’s protective ozone layer. Although it’s not clear what chemical scars it left, such a large smoke plume has the potential to trigger chemical reactions that destroy ozone.
This injured koala, cared for at the Kangaroo Island Wildlife Park in January, was among the countless animals harmed or killed by the bushfires that blazed across Australia this year.Lisa Maree Williams/Getty Images
The West on fire
Record-setting wildfires in the U.S. West also produced heartbreaking images: raging blazes, orange skies, destroyed homes, neighborhoods enveloped in acrid smoke (SN: 9/18/20). By mid-November, more than 9,200 fires in California had burned about 1.7 million hectares — more than double the acreage burned in 2018, the state’s previous record fire year. Meanwhile, Colorado battled three of the largest wildfires in the state’s history. Combined, those fires burned more than 219,000 hectares.
The role of climate change in these blazes is multipronged. From California to Colorado, rising temperatures due to climate change have led to earlier spring snow melting, resulting in drier vegetation by summer. In California, that extremely dry vegetation combined with a record-breaking heat wave primed the landscape for runaway fires (SN: 8/17/20).
Climate change is increasing the frequency of extreme climate conditions. California’s average heat and dryness in both summer and autumn have become more severe, dramatically increasing the number of days each year prone to extreme fire weather conditions (SN: 8/27/20). Simulations of future climate change project increasing dryness over at least the next few decades — which means 2020’s fire records aren’t likely to stand for long.
Siberian meltdown
From January through July, Siberia was in the grips of a powerful heat wave that led to record-breaking temperatures (SN: 6/23/20), unprecedented wildfires in the Arctic and thawing permafrost, which in turn may have led to the collapse of a fuel storage tank that flooded nearby rivers with diesel fuel (SN: 7/1/20).
A worker takes part in cleanup operations at a fuel spill in northern Russia. A heat wave thawed permafrost, which may have caused the collapse of a fuel tank in May that released about 20 million liters of diesel fuel.Denis Kozhevnikov/TASS/Getty Images
Such heat in Siberia — with temperatures as high as 38° Celsius (about 100° Fahrenheit) — would have been impossible without climate change (SN: 7/15/20). Human influence made the heat wave at least 600 times as likely — and possibly as much as 99,000 times as likely, scientists reported. Moreover, the carbon dioxide churned into the atmosphere by this year’s Arctic wildfires also smashed the previous record for the region, set in 2019 (SN: 8/2/19). That CO2 can beget further warming, and the fires can also speed up permafrost thaw, which could add more of another greenhouse gas, methane, to the atmosphere.
This year also saw the second-lowest extent of Arctic sea ice on record. Meanwhile, a roughly Manhattan-sized chunk of Canada’s Milne ice shelf — close to half of what had been the country’s last intact ice shelf — suddenly collapsed into the Arctic Ocean in August, carrying an ice-observing station away with it.
Supercharged hurricanes
As early as April, scientists predicted that the Atlantic hurricane season, which lasts from June 1 through November 30, would be busy, with about 18 named storms, compared with an average of 12 (SN: 4/16/20). By August, scientists upped their predictions to as many as 25 (SN: 8/7/20). But 2020 surpassed those expectations too: By mid-November, there were 30 named storms, eclipsing a record set in 2005 (SN: 11/10/20).
Hurricane Laura (shown whipping up the waves near Galveston, Texas, on August 26) rapidly intensified into a Category 4 storm before making landfall on August 27 in Louisiana.Thomas B. Shea/Getty Images
It’s difficult to link climate change to the number of storms that form in a given year. Very warm ocean waters, such as in the Atlantic Ocean this year, foster tropical cyclone formation. It’s true that those warm waters are linked to climate change, as the surface ocean swallows up excess heat from the atmosphere. But other factors are also involved in hurricane formation, including wind conditions, making it difficult to establish a link.
But there are established links between warming oceans and increasing hurricane intensity, as well as rainfall (SN: 9/13/18). Warm Atlantic waters gave a boost to the intense storms of the 2017 hurricane season, for example (SN: 9/28/18). The warm waters can also provide enough energy to give hurricanes extra staying power even after landfall (SN: 11/11/20).
And, as the world saw in 2020, very warm ocean waters can also speed up how quickly a storm strengthens — leading to dangerous, difficult-to-predict, suddenly supercharged storms. Such rapid intensification is defined as sustained wind speeds increasing by at least 55 kilometers per hour within just 24 hours. 2020 saw that in abundance, with 10 Atlantic storms rapidly intensifying in the region’s bathlike waters before making landfall. More