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This year, Arctic sea ice shrank to its second-lowest extent in more than 40 years of satellite measurements. Ice covered just 3.74 million square kilometres of Arctic waters at its annual summer minimum, reports the US National Snow and Ice Data Center (NSIDC). In only one other year — 2012 — has the annual minimum dropped below four million square kilometres. The near-record low is representative of a worrying trend in which “weather that used to be considered extreme is becoming the norm”, says the NSIDC report.
The city of Manaus, Brazil, might help to reveal what the terrible toll of coronavirus looks like when the virus rages almost unchecked. A preprint study, not yet peer reviewed, shows that between one in 500 and one in 800 people in the city died of the disease. Manaus is fairly young, with just 6% of its population over the age of 60 (in the United States, it’s around 20%). Researchers tested samples from blood banks and estimated that up to 66% of the city’s people have been infected, which they say helped to finally bring down the death rate despite conditions, such as overcrowding, that allow the virus to spread easily.
Reference: medRxiv preprint
Beaver dams create nature firebreaks and fireproof refuges for other animals, and they help ecosystems to recover from wildfires. Satellite images reveal that beaver homesteads are oases of green among wildfire-scorched areas of the western United States. “It doesn't matter if there’s a wildfire right next door,” says ecohydrologist Emily Fairfax. “Beaver-dammed areas are green and happy and healthy-looking.”
The historic first image of a black hole, unveiled last year, has now turned into a movie. The short sequence of frames shows how the material of the black hole’s surroundings is stirred into a constant maelstrom by gravity. To create the frames, the Event Horizon Telescope collaboration — which harnesses a planet-wide network of observatories — exhumed old data on the black hole and combined them with a mathematical model based on the image released in April 2019, to show how the surroundings have evolved over eight years.
Read more: Black hole pictured for first time — in spectacular detail (Nature | 7 min read, from 2019)
Features & opinion
People in some countries might get the short end of the stick when it comes to COVID-19 vaccines because of an inequality that lurks in the design of the vaccines themselves. Several leading vaccine candidates use mild viruses as delivery systems. But if people have been exposed to these mild viruses in the past, their immune systems might attack the delivery system itself. This could nullify the effect of the vaccine and, judging from the experience of a problematic HIV-vaccine candidate, even increase the risk of infection. Scientists are watching to see whether either of these outcomes will result from COVID-19 vaccines. But if they do, it’s more likely to happen to people in countries such as Thailand, Brazil or Cameroon, where exposure to these mild viruses is more common.
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With contributions by David Cyranoski