Solving the climate change attitude mystery, from Statistical Modeling, Causal Inference, and Social Science, originally from Wired.
The facts appear to be as follows: 19 percent of college-educated Republicans believe that human activites cause global warming; 75 percent of Democrats believe the same. Among the non-college-educated, 31 percent of Republicans have that belief and 52 percent of Democrats.
One conclusion is that college-educated people are more likely to toe the party line.
But here's another idea. The assumption underlying this seems to be that "Republican" and "Democrat" are fixed labels -- so clearly college makes you think that global warming is more likely if you're a Democrat, but less likely if you're a Republican. But of course those labels are not fixed; people can switch parties! So maybe what happens is that education doesn't change your beliefs -- but if you are the sort of person who would believe that humanity causes global warming, but otherwise tend to agree with Republicans, a college education would flip you to the Democratic side. (And vice-versa for Democratic-leaning global-warming-skeptics.) I'm not saying that there are people doing indoctrination at our colleges, but that such an education changes the way one looks at things.
It basically seems to be Simpson's paradox in different guise. You've got to be careful when the groups you're analyzing change size!
Showing posts with label global warming. Show all posts
Showing posts with label global warming. Show all posts
15 May 2008
04 December 2007
How much land is in the tropics?
In Tropics widen, fringe areas drier, experts say, from the Associated Press, I found the following quote:
In fact, the tropics make up about two-fifths of the globe. To be more precise, I mean that about two-fifths of the total area of the surface of the earth is between the two tropics. The tropics are at latitudes +23.5 and -23.5 degrees (I'll use + and - for north and south here.) So it's easy to see where the "one-quarter" figure might come from -- the tropics span a total of 47 degrees of latitude, out of the full range of 180, and 47/180 is essentially 1/4.
But there's an interesting fact about the surface area of a sphere. Take a sphere of radius r. Cut it with two parallel planes of distance h apart. Then the area of your slice will be h/(2r) times the surface area of the sphere, or 2πrh, regardless of the way the sphere is cut; notice that this is also the surface area of a cylinder of height h and radius r. I saw this demonstrated once, when I first saw this fact in a calculus class, by cutting a spherical loaf of bread into slices of equal thickness; the slices get varying amounts of the interior of the bread but all get the same amount of crust.
The thickness of the slice in question, for the tropics, is (2 sin(23.5o))r, where r is the radius of the earth. Thus this slice makes up sin(23.5o) = 0.398 of the earth, which is just under two-fifths. I knew from the moment I read this fact that one-quarter was an underestimate, but I suspected that perhaps it was more accurate than, say, "one-third". But it's not.
(The actual point of the article is not that the tropics make up one-fourth, or two-fifths, or whatever fraction of the earth, but that they are "widening"; this uses an atmospheric definition of the tropics which is different from the astronomical one implied by the quote above.)
Geographically, the tropical region is a wide swath around Earth's middle stretching from the Tropic of Cancer, just south of Miami, to the Tropic of Capricorn, which cuts Australia almost in half. It's about one-quarter of the globe and generally thought of as hot, steamy and damp, but it also has areas of brutal desert.
In fact, the tropics make up about two-fifths of the globe. To be more precise, I mean that about two-fifths of the total area of the surface of the earth is between the two tropics. The tropics are at latitudes +23.5 and -23.5 degrees (I'll use + and - for north and south here.) So it's easy to see where the "one-quarter" figure might come from -- the tropics span a total of 47 degrees of latitude, out of the full range of 180, and 47/180 is essentially 1/4.
But there's an interesting fact about the surface area of a sphere. Take a sphere of radius r. Cut it with two parallel planes of distance h apart. Then the area of your slice will be h/(2r) times the surface area of the sphere, or 2πrh, regardless of the way the sphere is cut; notice that this is also the surface area of a cylinder of height h and radius r. I saw this demonstrated once, when I first saw this fact in a calculus class, by cutting a spherical loaf of bread into slices of equal thickness; the slices get varying amounts of the interior of the bread but all get the same amount of crust.
The thickness of the slice in question, for the tropics, is (2 sin(23.5o))r, where r is the radius of the earth. Thus this slice makes up sin(23.5o) = 0.398 of the earth, which is just under two-fifths. I knew from the moment I read this fact that one-quarter was an underestimate, but I suspected that perhaps it was more accurate than, say, "one-third". But it's not.
(The actual point of the article is not that the tropics make up one-fourth, or two-fifths, or whatever fraction of the earth, but that they are "widening"; this uses an atmospheric definition of the tropics which is different from the astronomical one implied by the quote above.)
19 July 2007
Alaskan glaciers, and the snows of Kilimanjaro
My parents recently got back from a two-week trip to Alaska.
While in Alaska, they saw some glaciers. I remembered that in An Inconvenient Truth, Al Gore mentioned how some glaciers in the Alps have retreated quite a bit within the historical record, showing pictures from the late 19th century and comparing them to modern-day photographs. It turned out that some of the glaciers there have receded within the memory of the people who live there, but others have actually advanced.
It seems to me that the only way to know for sure if global warming is causing glaciers to retreat is to analyze a large number of them for which there is a historical record. (Although I'm not a climatologist, the Alps seem like the best site for such a study simply because people have been living there for quite some time.) Anecdotal evidence just isn't valid here. However, it seems like there are better ways of tracking temperature than looking at glaciers (for example, just looking at actual temperature numbers!) and so the glaciers are more a convenient symbol than anything, because miles-long ice formations seem like something that humans just couldn't possibly melt! What one person knows is simply an inadequate sample, although it can make for a powerful story.
The news of the moment regarding Al Gore and global warming seems to be that the snows of Kilimanjaro are retreating, but that's not due to global warming but rather due to a comparatively dry weather period over the last century or so. The retreat began about a hundred years ago, whereas global warming didn't really become a big effect on climate until maybe forty or fifty years ago. The ice on Kilimanjaro is sublimating, not melting. Philip Mote of the University of Washington has said that Gore shouldn't use Kilimanjaro as a symbol for global warming, as he has in the past. He suggests that [t]here are dozens, if not hundreds, of photos of midlatitude glaciers you could show where there is absolutely no question that they are declining in response to the warming atmosphere,". I agree. Scientists are often blind to the power of good symbols in getting across their message to non-scientists.
Mathematicians, more so.
While in Alaska, they saw some glaciers. I remembered that in An Inconvenient Truth, Al Gore mentioned how some glaciers in the Alps have retreated quite a bit within the historical record, showing pictures from the late 19th century and comparing them to modern-day photographs. It turned out that some of the glaciers there have receded within the memory of the people who live there, but others have actually advanced.
It seems to me that the only way to know for sure if global warming is causing glaciers to retreat is to analyze a large number of them for which there is a historical record. (Although I'm not a climatologist, the Alps seem like the best site for such a study simply because people have been living there for quite some time.) Anecdotal evidence just isn't valid here. However, it seems like there are better ways of tracking temperature than looking at glaciers (for example, just looking at actual temperature numbers!) and so the glaciers are more a convenient symbol than anything, because miles-long ice formations seem like something that humans just couldn't possibly melt! What one person knows is simply an inadequate sample, although it can make for a powerful story.
The news of the moment regarding Al Gore and global warming seems to be that the snows of Kilimanjaro are retreating, but that's not due to global warming but rather due to a comparatively dry weather period over the last century or so. The retreat began about a hundred years ago, whereas global warming didn't really become a big effect on climate until maybe forty or fifty years ago. The ice on Kilimanjaro is sublimating, not melting. Philip Mote of the University of Washington has said that Gore shouldn't use Kilimanjaro as a symbol for global warming, as he has in the past. He suggests that [t]here are dozens, if not hundreds, of photos of midlatitude glaciers you could show where there is absolutely no question that they are declining in response to the warming atmosphere,". I agree. Scientists are often blind to the power of good symbols in getting across their message to non-scientists.
Mathematicians, more so.
28 June 2007
help! the Earth is sinking!
Earth's inner heat keeps cities afloat. The rocks that the Earth is made of expand when it's warmer, like most materials; thus if the inside of the Earth were not as heat the Earth would be smaller.
Derrick Hasterok and David Chapman, of the University of Utah, say that the significance of this heating has been overlooked. In particular, it's stronger in some areas than in others -- the rock under the western U. S. is hotter than that under the eastern U. S., so the general fact that the West tends to be higher than the East is in part due to this phenomenon.
However, they claim that "New York would drop to 1,427 feet below the Atlantic ocean, Boston and Miami even deeper. Los Angeles would rest 3,756 feet below the surface of the Pacific ocean." This just doesn't feel right. Perhaps those places would fall to those heights below the current sea level -- I take this to mean they'd be slightly closer to the center of the Earth. But sea level would be redefined to be the new average height of the sea. The only way all these places could suddenly be under sea level is if there were more water.
In any case, it doesn't matter, because the heat is coming from radioactive decay of some very long-lived isotopes. Worry about global warming.
(Those of you who thought this blog was supposed to be about probability -- as the title might lead you to believe -- may be wondering why I'm making this post. But this blog is also about silly uses of mathematics in the media.)
Derrick Hasterok and David Chapman, of the University of Utah, say that the significance of this heating has been overlooked. In particular, it's stronger in some areas than in others -- the rock under the western U. S. is hotter than that under the eastern U. S., so the general fact that the West tends to be higher than the East is in part due to this phenomenon.
However, they claim that "New York would drop to 1,427 feet below the Atlantic ocean, Boston and Miami even deeper. Los Angeles would rest 3,756 feet below the surface of the Pacific ocean." This just doesn't feel right. Perhaps those places would fall to those heights below the current sea level -- I take this to mean they'd be slightly closer to the center of the Earth. But sea level would be redefined to be the new average height of the sea. The only way all these places could suddenly be under sea level is if there were more water.
In any case, it doesn't matter, because the heat is coming from radioactive decay of some very long-lived isotopes. Worry about global warming.
(Those of you who thought this blog was supposed to be about probability -- as the title might lead you to believe -- may be wondering why I'm making this post. But this blog is also about silly uses of mathematics in the media.)
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