* Astronomy

Fossil fuels should be 'phased out by 2100' says IPCC

The unrestricted use of fossil fuels must end soon if the world is to avoid dangerous climate change.
That's one of the key messages in a new report from the Intergovernmental Panel on Climate Change.
The IPCC outlines an approach that could see most of the world's electricity produced from low carbon sources by 2050.
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Title: How close is Earth to a runaway greenhouse?
Authors: Ramses M. Ramirez, Ravi kumar Kopparapu, Valerie Lindner, James F. Kasting

Recent calculations suggest that the inner edge of the habitable zone around the Sun could be as far out as 0.99 astronomical units (AU)- much closer to the orbit of Earth than had been thought. This reopens the question of whether future increases in atmospheric CO2 might trigger a runaway or moist greenhouse. A runaway greenhouse implies complete ocean vaporisation; a moist greenhouse implies that the stratosphere becomes wet, leading to ocean loss via hydrogen escape to space. Previous studies (Kasting and Ackerman, 1986) had indicated that neither a moist nor a runaway greenhouse could be triggered by CO2 increases of any magnitude. Here, we revisit this question with a 1-D climate model that includes updated absorption coefficients for CO2 and H2O, along with an improved parameterisation of tropospheric relative humidity. We find that a runaway greenhouse is still precluded. However, a moist greenhouse could conceivably be triggered by an 11-fold increase in atmospheric CO2, and humans could be subject to fatal heat stress for CO2 increases of (4-8)-fold. When this relative humidity parameterisation is used in our habitable zone calculations, the inner edge moves inward to 0.97 AU. Both of these calculations remain overly pessimistic, as relative humidity may increase more slowly than assumed and cloud feedback is probably negative in this temperature regime. Finally, we reexamine the lifetime of the biosphere against solar luminosity increases and show that older calculations suggesting ~0.5 Ga and 0.9 Ga as the lifetime for C3 and C4 photosynthesis are still approximately correct. Improvements in all of these estimates could be made with a properly formulated 3-D climate model that can self-consistently calculate relative humidity and cloud feedbacks.

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NRL Scientists Detect Carbon Dioxide Accumulation at the Edge of Space

A team of scientists from the Naval Research Laboratory, Old Dominion University, and the University of Waterloo reports the first direct evidence that emissions of carbon dioxide (CO2) caused by human activity are propagating upward to the highest regions of the atmosphere. The observed CO2 increase is expected to gradually result in a cooler, more contracted upper atmosphere and a consequent reduction in the atmospheric drag experienced by satellites. The team published its findings in Nature Geoscience on November 11, 2012 (10.1038/NGEO1626).
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Arctic melt releasing ancient methane

Scientists have identified thousands of sites in the Arctic where methane that has been stored for many millennia is bubbling into the atmosphere.
The methane has been trapped by ice, but is able to escape as the ice melts.
Writing in the journal Nature Geoscience, the researchers say this ancient gas could have a significant impact on climate change.
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