Greenland at point of no return

So much ice has melted from Greenland’s glaciers that even if global warming were to stop today, the island’s ice sheet would keep on disintegrating. That’s the conclusion of a new study that examined 34 years of satellite data on 234 glaciers across Greenland, reports USA Today. The island’s ice sheet dumps more than 300 billion tons of melting ice into the ocean every year, making it the single-biggest contributor to global sea level rise. Researchers say the rate of collapse, which has increased at least sevenfold over the past two decades, is now so drastic that the snowfall that typically replenishes the glaciers can no longer keep up with the rate of melting from parts of the ice sheet newly exposed to warmer ocean water—even if humanity somehow managed to reverse climate change. “Glacier retreat has knocked the dynamics of the whole ice sheet into a constant state of loss,” says study co-author Ian Howat, from Ohio State University. Greenland’s disappearing ice sheet is a problem for all of humanity: Sea levels are expected to rise by more than 3 feet by 2100, swamping many coastal communities.

or vaccinated that the virus can no longer spread widely—may be closer than previously thought. Early in the pandemic, epidemiologists estimated that the threshold was 70 percent of a given population. But more than a dozen scientists told The New York Times that statistical modeling suggests that herd immunity might occur at 50 percent, or possibly even lower. Some say that particularly hard-hit neighborhoods may already be there. “I’m quite prepared to believe that there are pockets in New York City and London that have substantial immunity,” says Harvard epidemiologist Bill Hanage. But other epidemiologists warn that focusing on herd immunity is a distraction and could encourage people to abandon measures proven to reduce spread, such as mask wearing. Antibody testing has shown that no city or country is yet close to a 50 percent previous-infection rate; only 10 percent of the global population has Covid-19 antibodies. “We’d be playing with fire if we pretended we’re done with this,” says Jeffrey Shaman, an epidemiologist at Columbia University.