Arctic permafrost has become a recent star in the climate change conversation, capturing the attention of scientists, activists and policymakers alike because of its ability to emit large quantities of carbon dioxide as well as methane — a particularly potent though relatively short-lived greenhouse gas — when it thaws. As temperatures rise in the Arctic, scientists are increasingly concerned that permafrost will become a major contributor to the greenhouse gas emissions driving global warming.

Studies of permafrost emissions are important in both estimating current levels of greenhouse gas emissions and making predictions for the future. So far, most studies have focused on the way permafrost behaves in the summer, when Arctic temperatures are at their highest. But a new paper in Proceedings of the National Academy of Sciences says we’ve been overlooking the importance of cold-season emissions of methane gas in particular — and possibly underestimating their impact in the future.

“The cold period in general is the time of the year that is warming the fastest in these Arctic ecosystems,” said the new study’s lead author Donatella Zona, an assistant professor at San Diego State University and research fellow at the University of Sheffield.

Until recently, scientists have known very little about how much methane is released by permafrost during the cold winter months, she said. But she noted, “Really, if we’re thinking about the future of climate change, we need to understand if this time of the year is important.”
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Amplifying positive feedback Adds up to an extra 2.0C by 2100

The feedback between climate and the carbon cycle is positive in the 21st century and beyond. Models indicate a loss of carbon of 59 [20 to 98] PgC and 17 [13 to 21] PgC per °C warming from the land and the ocean, respectively [this is about 0.5C by 2100, but does not include large forest die-back, peat-lands and large Arctic feedback sources].
Permafrost feedback Until the year 2100, up to 250 PgC [picograms of carbon] could be released as CO2, and up to 5 Pg as CH4. Given methane's stronger greenhouse warming potential, that corresponds to a further 100 PgC of equivalent CO2 released until the year 2100 [so 350 PgC and about 1.5°C]. (AR5 WG1 FAQ 6.1)​

Researchers at the National Snow and Ice Data Center estimate that by 2200, 60% of the Northern Hemisphere's permafrost will probably be melted, which could release around 190 billion tons of carbon into the atmosphere. This amount is about half of all the carbon released in the industrial age. The affect this will have on the rate of atmospheric warming could be irreversible. At the very least, these estimates mean fossil fuel emissions will have to be reduced more than currently suggested to account for the amount of carbon expected to discharge from melting permafrost.

Now, an international team, led by researchers at MIT's Haystack Observatory, has for the first time measured the radius of a black hole at the center of a distant galaxy—the closest distance at which matter can approach before being irretrievably pulled into the black hole.

The scientists linked together radio dishes in Hawaii, Arizona and California to create a telescope array called the "Event Horizon Telescope" (EHT) that can see details 2,000 times finer than what's visible to the Hubble Space Telescope. These radio dishes were trained on M87, a galaxy some 50 million light years from the Milky Way. M87 harbors a black hole 6 billion times more massive than our sun; using this array, the team observed the glow of matter near the edge of this black hole—a region known as the "event horizon."

"Once objects fall through the event horizon, they're lost forever," says Shep Doeleman, assistant director at the MIT Haystack Observatory and research associate at the Smithsonian Astrophysical Observatory. "It's an exit door from our universe. You walk through that door, you're not coming back."


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Caught up in this spiraling flow are magnetic fields, which accelerate hot material along powerful beams above the accretion disk The resulting high-speed jet, launched by the black hole and the disk, shoots out across the galaxy, extending for hundreds of thousands of light-years. These jets can influence many galactic processes, including how fast stars form.

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According to Einstein's theory, a black hole's mass and its spin determine how closely material can orbit before becoming unstable and falling in toward the event horizon. Because M87's jet is magnetically launched from this smallest orbit, astronomers can estimate the black hole's spin through careful measurement of the jet's size as it leaves the black hole. Until now, no telescope has had the magnifying power required for this kind of observation.




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Abstract

Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by the accretion of matter onto supermassive black holes. Although the measured width profiles of such jets on large scales agree with theories of magnetic collimation, the predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 ± 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.