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Long lines. Narrow seats. Baggage fees. You recognize this list. It's the downside of flying on modern commercial airlines. And now we have a new item to add: neutrons.
Spaceweather.com and Earth to Sky Calculus have just completed a 5-continent survey of cosmic ray neutrons at aviation altitudes. From Dec. 2018 through Feb. 2019, Hervey Allen of the University of Oregon's Network Startup Resource Center carried Earth to Sky radiation sensors including neutron bubble chambers onboard commercial flights from North America to Europe, Africa, South America and Asia. Neutrons from deep space were detected on every flight.
Hervey logged 83 hours in the air as he traveled 41,500 miles above 30,000 feet. For reference, that's almost twice the circumference of the Earth. The entire time, he gathered data on X-rays, gamma-rays and neutrons in an energy range (10 keV to 20 MeV) similar to that of medical radiology devices and "killer electrons" from the Van Allen Radiation Belts.
The results were eye-opening. During the trip, Hervey recorded 230 uGy (microGrays) of cosmic radiation. That's about the same as 23 panoramic dental x-rays or two and a half chest X-rays. Moreover, 41% of the dose came in the form of neutrons. This confirms that cosmic-ray neutrons are abundant at aviation altitudes and must be considered in any discussion of "Rads on a Plane."
https://spaceweatherarchive.com/2019/03/12/neutrons-detected-on-commercial-airplane-flights/
(Score: 4, Informative) by Immerman on Friday March 15 2019, @02:55PM (11 children)
Funny thing about water - it doesn't stop evaporating until you either lower the temperature or saturate the atmosphere. And water is a potent greenhouse gas, the more water there is in the atmosphere, the higher the temperature climbs, and the more water is required to saturate it.
Water alone is self-limiting in that runaway process, since the increase in temperature from adding 1 unit of water to the atmosphere is insufficient to increase the saturation point by one full unit worth of water - so the humidity increases, and precipitation becomes more likely. CO2 doesn't have that problem though - it just increases the temperature, which causes more water to evaporate just to maintain the same percent humidity. At the current temperature (14C average) , increasing the atmospheric temperature by only 1*C increases the amount of water the atmosphere can hold by at the same %humidity by almost 7%. Which means about 7% more greenhouse gasses in the atmosphere. Which, since water is the primary greenhouse gas, likely means somewhere around an 7% increase in the total greenhouse warming (which is currently somewhere around 32C), or an additional 2.2C. And as temperatures increase the effect gets more dramatic - at 20C the water content increases by 9% per degree, and the effect just keeps getting larger the hotter it gets.
(Score: 0) by Anonymous Coward on Friday March 15 2019, @03:23PM (7 children)
The energy to evaporate the water will also increase as the pressure rises. At Venus pressures water doesn't boil until 300 C:
https://www.engineeringtoolbox.com/boiling-point-water-d_926.html [engineeringtoolbox.com]
(Score: 2) by Immerman on Friday March 15 2019, @03:52PM (6 children)
Evaporation doesn't rely on boiling, and happens at pretty much any temperature. It accelerates as you approach boiling, and slowing it will reduce the equilibrium humidity somewhat, but it's not going to fundamentally alter the process.
Especially if we're only talking 2atm instead of Venus's 90atm. Assuming vaporization was the primary cause of atmospheric pressure increase, we'd be talking about ~103% of the current atmospheric mass being water, instead of 3%. So about 33x the amount of greenhouse gasses. That might not be truly Venus-like, but it'd be close enough that we couldn't survive.
(Score: 0) by Anonymous Coward on Friday March 15 2019, @04:07PM (5 children)
If you want Temperatures like Venus you need pressures like Venus (even higher since Earth is farther from the sun). You can find ~1.5 atm down some mineshafts and see the temperature already rises 42 K:
http://nopr.niscair.res.in/bitstream/123456789/2506/1/IJRSP%2037%281%29%2064-67.pdf [niscair.res.in]
(Score: 2) by Immerman on Friday March 15 2019, @04:24PM (2 children)
I don't want temperatures like Venus - temperatures too high to support complex life are quite sufficient for us to be "Venus-like" enough for me.
(Score: 0) by Anonymous Coward on Friday March 15 2019, @04:33PM (1 child)
Which is what temperature? The moon goes up to nearly 400 K, so if you aren't worried about the pressure aspect then I would say you are thinking more of a "moon-like" than "venus-like" situation.
https://www.sciencedirect.com/science/article/pii/S0019103516304869 [sciencedirect.com]
(Score: 2) by Immerman on Friday March 15 2019, @04:47PM
Peak temperatures are rather irrelevant, you can always find somewhere to hide. And the Moon's average temperature varies between 215K at the equator, to 104K above 85* latitude.
Meanwhile the Earth's average is currently 287K, and only has to increase by 86C to make it awful difficult to find liquid water on the surface (well, a bit more to compensate for increased pressure, but even increasing it to 10atm only increases the boiling point by about 70C, we don't have to get anywhere near Venus's average of 735K to make life as we know it impossible.
(Score: 1) by khallow on Friday March 15 2019, @05:55PM (1 child)
Because the Earth is warm. From your article:
(Score: 1) by khallow on Friday March 15 2019, @05:56PM
(Score: 2) by HiThere on Friday March 15 2019, @04:59PM (2 children)
I think you left out black body radiation. As the temperature of the earth increases, the amount of heat it radiates increases. IIRC this is a fourth power law. So it should mean you are overestimating the rise in temperature. (By how much, though?)
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by Immerman on Friday March 15 2019, @05:21PM (1 child)
Not really - that's doesn't factor into things as much until you start looking at the *consequences* of the increased greenhouse gasses. If you increase the planet's temperature by 1*C, you increase the water in the atmosphere by somewhere around 7% to maintain equilibrium humidity.
Now, the consequences of increasing the amount of greenhouse gasses by 7% get more complicated - they make the atmosphere less transparent to IR (the frequency at which something the Earth's temperature radiates most black-body radiation), which means that the Earth must get warmer in order to radiate enough energy to restore equilibrium with the incoming solar radiation (very little of which is IR, because the sun is hot enough to radiate primarily in the visible spectrum)
Figuring out how much additional warming must occur to reach that new thermal equilibrium is where the black black-body formula comes into play, and means (along with other non-linearities) that the 7% increase in greenhouse gasses won't cause a full 7% increase in greenhouse warming (currently estimated at around 36C total, based on the discrepancy between measured and theoretical temperatures of something with the Earth's albedo). A simple linear extrapolation would expect that 7% increase in water to cause a about 2.5C of further warming.
However, there's also the fact that that increased warming will put even *more* water into the air to maintain stable humidity. Even if the actual temperature change associated with that 7% increase is only half the linear prediction, 1.25C, that still means you're going to further increase the amount of water in the air by another ~9% to maintain the same humidity. (and of course, that 9% will cause even more warming, which will cause even more evaporation...)
Meanwhile, at Earth's average temperature of about 288K, a 1C increase will only increase the black-body radiation by about (289/288)^4 -1 = 1.4%. If a 7% increase in greenhouse gas mapped directly to a 7% decrease in the transparency of the atmosphere to IR, you would need to increase the temperature to around 293K, a 5C difference, in order to restore energy equilibrium.
(Score: 2) by HiThere on Friday March 15 2019, @07:47PM
Thank you. I couldn't have even estimated that.
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