You can’t make this stuff up.
Mann also threw a high, hard one at McCarver’s theory, saying that the carbon emissions behind climate change may even lower home runs. “If anything, anthropogenic carbon emissions and global warming should make the atmosphere slightly heavier, because we’re taking carbon that was trapped in the solid earth and releasing to the atmosphere (in the form of CO2), and a warmer atmosphere will hold more water vapor. Both CO2 and water vapor contribute (slightly) to the mass of the atmosphere.”
Is Global Warming Causing More Home Runs in Baseball?: Scientific American
McCarver is correct that a warmer atmosphere is less dense than a cooler atmosphere. The Ideal Gas Law (PV = nRT) tells us that a higher temperature makes the volume increase, which means the air is less dense. That is why the troposphere is much thicker at the equator than at the poles. It is also why planes sometimes can’t take off from the Phoenix airport – the air isn’t dense enough on very hot days to provide the needed lift.
As far as Mann’s claim that more water vapor means a “heavier atmosphere” – that is just plain ignorant. The molar mass of H2O is 18g, compared to 28g for N2 and 32g for O2. If an H2O molecule displaces an N2 or O2 molecule, the density of the atmosphere decreases. Increasing CO2 by 0.0001 mole fraction isn’t going to do jack to the density of the atmosphere.
Of course, these are the same geniuses who believe that the missing heat sank to the bottom of the ocean.
Steve, sorry to say that, but water is beeing dissolved in air. The water molecules don’t replace air molecules so the air becomes indeed heavier.
http://www.engineeringtoolbox.com/molecular-mass-air-d_679.html
“Note! Water vapor in air will replace other gases and reduce the total density of the mixture. Dry air is more dense than humid air!”
No. Air under atmospheric conditions is reasonably modeled as an ideal gas (as Steve has implied). In fact, in addition to the molecular weight effect, one can reasonably argue that the molecular weight effect of water is accentuated by the conditions that promote water evaporation (low pressure).
Rewritten, the ideal gas law is: density = (mol. wt.) x P / (RT)
Due to its trace concentration, the effect of CO2 on air density is negligible.
Wow, Mann really is dumb to the extreme. I figured this out years ago…long before I had any degrees. I had the complete quantitative mechanism down early in college. If he’s getting this wrong, he’s not understanding something that I’d be willing to put in an exam for freshmen chemistry (quantitatively I might add). CO2 concentration has essentially a negligible effect on the density of air…completely swamped out by just a few tenths of a degree of change. So the only way Mann’s conclusion is right (and we know for sure that his mechanism is wrong) would be if the humidity decreased substantially. Of course, he’d never admit that decreasing humidity is even a remote possibility. 😉
-Scott
Don’t we also need to consider greater attendance by fatter Americans? This would exert more gravitational force thus increasing air pressure in the ballparks.
Good point. But cars are smaller now which reduces the gravitational pull in the parking lot.
Mann has once again solidified his credentials as a physical scientist.
Well, Mann may have been referring to the mass of the atmosphere, not the density. Heavy is a measure of weight, which is mass x acceleration due to gravity.
It would make sense that any mass we extract from the Earth and put it in the atmosphere will increase the mass of that atmosphere.
Not sure which direction the avg density of air heads if you put both more CO2 (molecular weight more than air) and H20 (molecular weight less than air), but regardless, the effect will be negligible compared to other confounding variables.
Mann call himself a scientist but seems to have little appreciation of signal-to-noise ratio and confounding variables.
For the game of baseball, the biggest confounding variable in this discussion is the quality of pitchers vs. hitters. Sad to see the Chicago Cubs already at midseason form (8-15, second worst in NL).
He was talking about drag on baseballs, which is a function of density. The total mass of the atmosphere is irrelevant to that discussion.
Whose on first!
http://www.youtube.com/watch?v=sShMA85pv8M