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RE: Greenhouse Gases
 
 


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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NASA Ozone Study May Benefit Air Standards, Climate

A new NASA-led study finds that when it comes to combating global warming caused by emissions of ozone-forming chemicals, location matters.
Ozone is both a major air pollutant with known adverse health effects and a greenhouse gas that traps heat from escaping Earth's atmosphere. Scientists and policy analysts are interested in learning how curbing the emissions of these chemicals can improve human health and also help mitigate climate change.

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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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Sky-high methane mystery closer to being solved, UCI researchers say

Commercial natural gas was likely major factor in late-20th century stabilisation

Increased capture of natural gas from oil fields probably accounts for up to 70 percent of the dramatic levelling off seen in atmospheric methane at the end of the 20th century, according to new UC Irvine research being published Thursday, Aug. 23, in the journal Nature.
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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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CO2 storage site
 
 


Seabed test mimics carbon dioxide release

Scientists are beginning a month-long experiment in Scottish waters to study the impact of a possible leak from an undersea carbon dioxide storage site.
Working in Ardmucknish Bay near Oban, researchers will allow CO2 to bubble through sediments from a buried pipe and look for impacts on marine life.
Capturing CO2 from power stations and burying it under the seabed is viewed as an important global warming fix.
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  CO2 from fossil fuels discerned from natural sources

Researchers have demonstrated a way of distinguishing between carbon dioxide in the air coming from fossil fuel burning and that from natural sources.
It measures one type, or isotope, of carbon that decays over time - long since gone from fossil fuels.

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Greenhouse gas levels hit record in 2010

The amount of greenhouse gases in the atmosphere reached a record level in 2010 and rose faster last year than the average over the past decade, the annual Greenhouse Gas Bulletin published by the World Meteorological Organization on Monday said.
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"Missing" Global Heat May Hide in Deep Oceans

The mystery of Earth's missing heat may have been solved: it could lurk deep in oceans, temporarily masking the climate-warming effects of greenhouse gas emissions, researchers reported on Sunday.
Climate scientists have long wondered where this so-called missing heat was going, especially over the last decade, when greenhouse emissions kept increasing but world air temperatures did not rise correspondingly.

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New theories over methane puzzle

Scientists say that there has been a mysterious decline in the growth of methane in the atmosphere in the last decades of the 20th century.
Researchers writing in the journal Nature have come up with two widely differing theories as to the cause.
One suggests the decline was caused by greater commercial use of natural gas, the other that increased use in Asia of artificial fertiliser was responsible.
Both studies agree that human activities are the key element.

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