Wikipedia:Reference desk/Archives/Science/2015 August 8

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 8

How much would oxygen density at the Empire State Building affect athletics?

Theoretically, how much longer should 15 minutes worth of running at sea level take at the World Trade Center observatory? 1 second? Seconds? Fractions of a second? Could you gain a second or something just by running at the Dead Sea? And even more in a deep mine? This would be hard to test in practice as you'd need to do this at a single indoor site with a gas mask to control for the effects of temperature and humidity on air density (and performance!), wind, local gravity, and air resistance (which would exist even on a treadmill (arms and legs)). I'm also not sure if the small effect would be statistically significant with a practical number of subjects. But some sports scientist might have a curve for just the hypoxia effect. Sagittarian Milky Way (talk) 00:20, 8 August 2015 (UTC)

Some of these buildings are over a thousand feet tall - so there's a non-negligible change in air pressure. My rule of thumb is about one inch of mercury for each thousand feet - equivalently, that's nearly 5% less oxygen at the top of the Empire State Building than at sea level!

Whether this actually affects your running performance is up for debate. There's a huge amount of research on it, and it's not just as simple as "less oxygen, therefore lower performance." Here's a great review paper, Effects of Altitude Training on Running Performance - it looks like a student report, but it's done all the hard work of finding more research to read! The author surveyed over a dozen prior studies and found nearly equal numbers where the effects of altitude made the runner perform better, worse, or had no effect. These studies used a variety of methods, including simulated altitude in hypobaric chambers, and studies of athletes at much higher elevations than a building.

Nimur (talk) 01:13, 8 August 2015 (UTC)

Translated the above into normal units "Some of these buildings are over 300 metres tall - so there's a non-negligible change in air pressure. My rule of thumb is about 1.1 kPa per 100 metres - equivalently, that's nearly 5% less oxygen at the top of the Empire State Building than at sea level!" You're welcome. Fgf10 (talk) 11:05, 8 August 2015 (UTC)

"Metric" does not equate to "Normal". ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:19, 8 August 2015 (UTC)

For the vast majority of the world's population it does exactly that. Get with the times. Fgf10 (talk) 09:35, 9 August 2015 (UTC)

"Conformism" does not equate to "Normal". ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:59, 9 August 2015 (UTC)

You know, people don't realize that English base units are usually more human scaled than metric ones. But old base units being conveniently sized is only natural and metric is a slave to whatever the size of the Earth turned out to be (hint: about as big as possible without making the decimeter look big enough). This is why the foot is used more than the yard (0.9144 m) despite both being in the first group of units that kids learn. The pound is a better size for the base unit than the kilo because it's the size of one meal — a kilo is more than a loaf of bread, more like two meals. The capacity of mugs and glasses and cups and beers are between a cup and a pint (which is a pound of water). A liter is too huge for one sitting unless you're in a desert.

An acre is a better size for the minimum non-fractional amount of land than a hectare. It is the size of the largest square of land (excluding streets and sidewalks) in a city where the streets are close together. It is the size of a large exurban McMansion lot. If you've ever been to the old Twin Towers which are almost exactly square acres it's the size where it starts to look like land instead of uh, too small to be real land (the edge is no more than 3 degrees from the horizon for a standing man in a square acre). It's one day's work for a farmer before the Industrial Revolution. It is the size of a large but not huge skyscraper footprint. The Fahrenheit scale is better for weather. 0 was the coldest temperature early European scientists had access to (both natural and artificial) and 100 the hottest (meteorological one). That seems better for meteorology than all the usable weather temperatures being crammed into about -20 to like 50. Admittedly Celsius or Kelvin is better for the lab and astronomy and the US system sucks at small lengths and weights. (Inches and ounces are the smallest things with much use.) Sagittarian Milky Way (talk) 04:34, 10 August 2015 (UTC)

Indeed. I ought to have said: "my rule of thumb, which is accurate enough to provide a cited source,(PHAK, Chapter 7-5 Setting The Altimeter) ... is one inch of pressure for each one thousand feet." If you convert units and round the numbers, you're losing accuracy, and the onus is on you to find a source to support the rule you just made up. (Let us hope that your rule of thumb never puts you fifty feet, or approximately 20 meters, in the wrong direction - a slight rounding error can have dire consequences!) Nimur (talk) 14:03, 8 August 2015 (UTC)

It's more like 400 meters. The Dead Sea coincidentally is 400 meters in the other direction. The World Trade Center's neighborhood is lower so it's observatory is actually barely higher than the Empire State Building's second observatory. Sagittarian Milky Way (talk) 13:55, 8 August 2015 (UTC)

Don't forget to account for local gravity. 64.235.97.146 (talk) 13:48, 10 August 2015 (UTC)

What is the purpose of the pigments in our bodies?

For example, what is the purpose of the pigments in the eyes. Not all people have pigments in their eyes (people with blue eyes)5.28.163.245 (talk) 02:25, 8 August 2015 (UTC)

The three main types of biological pigments in human bodies are (1) protective, such as melanin, (2) sensitive, such as visual pigments, and (3) bioactive, such as hemoglobin. Hair, skin, and eye color pigments are primarily protective, but they along with blood flow serve in sexual selection, and blondism seems to encourage nurturing. Many bodily substances are photoreactive, such as vitamin precursors, although they don't contribute greatly to body coloration except in such cases as carotenosis. Pigments and the visual spectrum aren't accidentally related. It is molecules which can easily transition between an excited and non-excited state without being destroyed which react by giving off or absorbing photons in the range of the visual spectrum. μηδείς (talk) 03:23, 8 August 2015 (UTC)

Blondism seems to encourage nurturing? That's an interesting concept I haven't heard before - do you have a reference for it? Richerman (talk) 08:45, 8 August 2015 (UTC)

Blond or ginger coloration is not uncommon in the young of primates such as gibbons and some monkey species in which the parents have dark coloration (and vice-versa). There's speculation this either leads to nurturing (see also, Beak#Gape) or that it signals sexual immaturity, to prevent infanticide by rival males. I thought we had an article, but can't seem to find it. See primate coloration ginger baby monkey in the meantime. μηδείς (talk) 17:17, 8 August 2015 (UTC)

Says who? Blondism encourages me being turned off if it comes with looking kind of like Seven of Nine's actress. Not having Seven's weird, odd facial features features (Finnish women and some Swedes, Norwegians etc. don't) are still very beautiful though. I'm sure there's people who think Seven of Nine is the bee's knees. Sagittarian Milky Way (talk) 14:11, 8 August 2015 (UTC)

For the same reason birds have bright colored feathers. Erunaquest (talk) 10:29, 8 August 2015 (UTC)

How so? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:18, 8 August 2015 (UTC)

That's a further troll-ish contribution of Erunaquest. It's getting harder to assume good faith.--Scicurious (talk) 16:40, 8 August 2015 (UTC)

To specifically answer the original question, the purpose of the pigments in the iris is to block light from entering the eye. As the article says, the iris is the eye's aperture stop, just like the one in a camera. Also, people with blue eyes do have pigment in the iris, just less in some parts. See the eye color article. People who totally lack pigment in the iris have albinism. --108.38.204.15 (talk) 22:51, 8 August 2015 (UTC)

A little-known protective pigment is 3-Hydroxykynurenine, which colors the lens of the eye to keep UV from reaching the retina. Another is neuromelanin, which seems to be somewhat heterogeneous in nature [1] and occurs in various parts of the nervous system like substantia nigra, locus coeruleus, retinal pigment epithelium and even the inner ear. I thought its role in the RPE was light-blocking, but that ref suggests it has a general tendency to mop up free radicals ... not sure now, I should look further... Wnt (talk) 00:47, 9 August 2015 (UTC)

How much CO2 is too much, and how do you calculate it?

Besides the bureaucratically established compromise to reduce CO2 emission level by a set amount, what does nature need?

How much CO2 is too much, and how do you calculate it? How much CO2 can the natural sink safely? What total CO2 (or other greenhouse gases) generation is acceptable?--Scicurious (talk) 16:01, 8 August 2015 (UTC)

For the carbon sinks in the carbon cycle, see this nice graphic from NOAA that shows the major planetary carbon fluxes - [2]. ESRL.NOAA.gov has lots of other great resources that give good reliable information relative to your question. SemanticMantis (talk) 17:55, 8 August 2015 (UTC)

The question is not meaningful unless more context is provided. "Too much" for what? Short Brigade Harvester Boris (talk) 18:02, 8 August 2015 (UTC)

For affecting the food supply? For causing catastrophic sea rise? For making certain regions of the planet inhabitable? For killing the polar bears? These are all too much. Basically, for changing life on Earth as we know it.--Scicurious (talk) 20:25, 8 August 2015 (UTC)

In order: (1) Any increase in CO2 will affect the food supply. For a more detailed response you need to specify how large an effect, and on what components of the food supply. (2) Define "catastrophic" (e.g., how many meters). (3) What regions do you want to make inhabitable? You also need to define "inhabitable" (people live in all sorts of places that many would consider inhospitable, such as the Sahara or Greenland). (4) Killing the polar bears: we're partway there. See our article Polar_bear#Climate_change as well as Arctic sea ice decline. (5) "Change" needs to be defined: how large a change, and on what kinds of life? In the broadest sense we've already changed life on Earth, both through climate change as such and ancillary effects of CO2 rise such as ocean acidification. Short Brigade Harvester Boris (talk) 21:38, 8 August 2015 (UTC)

• I am starting to wonder whether you are pedantic or a global warming denialist.

• Re-formulating: how much CO2 is too much, if you don't want the average temperature to rise 1 degree Celsius above the level of 1880?--Scicurious (talk) 23:01, 8 August 2015 (UTC)

OK, a specific question, to which we can give a specific answer. There is abundant evidence that the equilibrium climate sensitivity is very likely to be 3 degrees C (or slightly less) for a doubling of CO2. Given a CO2 concentration of about 290 ppm in 1880 we expect a 1 C temperature rise to be reached a few decades to a century after attaining CO2 of 360 ppm. (The delay is because it takes some time for the system to reach equilibrium.) Since we reached 360 ppm around 1995 and the current temperature increase is about 0.8 C over the 1880s, our estimate seems reasonable. So the answer to your question "How much CO2 is too much, if you don't want the average temperature to rise 1 degree Celsius above the level of 1880?" is about 360 ppm, which we reached a couple decades ago.

I can assure you that as a Contributing Author to the three most recent IPCC Assessment Reports I am not a global warming denialist. Admittedly I may come across as pedantic but that's just my ingrained mindset that demands well posed questions. Short Brigade Harvester Boris (talk) 00:02, 9 August 2015 (UTC)

• OK, sorry for the comment above. I was wondering if you were trying to lead the discussion to the point where someone says "it's not possible to know how the climate changes."
• Follow-up question. So, along the same lines, how do tones of CO2 emissions correlate with CO2 ppm in the atmosphere? If we decided to reduce the present level (the figure that I have for 2015 is 401.30 ppm) back to 350 ppm, say, within 30 years, and stabilize it at that level. How much CO2 could we still emit? --Scicurious (talk) 01:21, 9 August 2015 (UTC)

In order to reduce CO2 to 350 ppm within 30 years we could emit no CO2 at all. In other words natural sinks are nowhere near sufficient to draw down that much CO2 in that short a time -- we'd instead have to invent a method to actively remove large amounts of CO2 from the atmosphere. You may be interested in this article by David Archer. Short Brigade Harvester Boris (talk) 03:09, 9 August 2015 (UTC)

200 million years ago the CO2 content of the atmosphere was about 4-5 times higher than present day (average of various estimates)- which is when the first crocodiles evolved. 100 million years ago it was about 2.5 times present day, which is when birds and marsupials evolved. Of course long before either of those dates bony fish had been around. So it seems a recognisable form of our biosphere can cope with much higher CO2 levels than we can reach with the aid of fossil fuels. Greglocock (talk) 22:06, 8 August 2015 (UTC)

"Recognizable" to who? Not to humans. The point is that anthropogenic global warming is a threat to human civilization as it currently exists. Yes, life on Earth will of course go on regardless of what we humans do to our environment. Human life very well might not. Anyone who knows about evolutionary history knows that Earth's environment has differed wildly over its history. The thing is, when those changes happen, organisms that aren't adapted to the new environment die. --108.38.204.15 (talk) 22:26, 8 August 2015 (UTC)

Greglocock's scenario looks like an post-apocalyptic Earth plagued by insects and other creatures.--Scicurious (talk) 23:01, 8 August 2015 (UTC)

and crocodiles, birds and mammals... which is why I explicitly included them. Your next job is to work out what CO2 content is available if we burnt all the fossil fuels in the ground. At least one estimate I've seen is quite low. Greglocock (talk) 02:23, 9 August 2015 (UTC)

Oh, yes, I forgot about the cute crocos, and little birds. Does this scenario include 7 billion human beings, or does it imply decimating the human race? Calculating this would be related to my follow-up question above. --Scicurious (talk) 03:06, 9 August 2015 (UTC)

Proven reserves of coal are say 1e15 kg, co2 is about 4 times heavier than carbon, so say 4e15 kg of co2. earth atmosphere is say 5e18 kg, so if you were to burn all the proven reserves of coal in one go that's about 800 ppm on top of the current 400 ppm. That isn't all the fossil fuels remaining, obviously, but then it is an unlikely scenario. Late edit - OOps, that's by weight not volume. I think you need to divide each mass by the mass per molecule, air is 28 ish, co2 is 44, so I think that leaves the extra co2 at 28/44*800 ppm, about 600. Greglocock (talk) 07:31, 9 August 2015 (UTC)

Oil reserves are between 1.2 trillion barrels ("proven" reserves) and 4.8 trillion ("known" reserves). Burning one barrel of crude oil results in 317kg of CO2. So between 0.4e15 and 1.5e15 kg more from the oil. Natural gas ("proven") reserves are around 187 trillion cubic meters and "known" reserves are about three times that amount. Burning a cubic meter of natural gas produces 2.1kg of CO2...so we have another 0.4e15kg to 1.2e15kg from that source. So oil and gas add about 0.8e15 to 2.7e15 to the 4e15kg of CO2 we'd get from coal. So with all sources of CO2 added together, we're looking at maybe 800 to 1000 ppm of CO2.

That's well below the toxic limit set by the OSHA (5000ppm) - but it's definitely not healthy! However, CO2 is heavier than oxygen and nitrogen, so we'd expect the concentration to be much higher at sea level than throughout the entire atmosphere (as implied by Greglocock above) - and it's pretty clear that if we burned all of the available coal, oil and natural gas, then most forms of life (including humans) would go extinct.

There are additional concerns though - it doesn't take a very large increase in ocean temperatures to cause the deep ocean Methane clathrate deposits to melt and dump methane into the atmosphere. If we captured it and burned that, we'd add another 1e15 to 5e15 kg of CO2...but a worse-case scenario is if we DON'T capture it because methane is 40 times worse than CO2 as a greenhouse gas.

Deforestation is another effect to consider. Not only do the trees we cut down tend to wind up as CO2 - increasing the total beyond what fossil fuels are doing - but also a reduction in the ability for plant life to absorb CO2 means that we take an increasing hit from natural sources. Increasing the number of ruminant animals that we farm for food is another problem because they take plants and turn them into methane instead of CO2 - which (as I explained) is a far, far worse greenhouse gas. The melting of permafrost releases more greenhouse gasses, and the production of cement adds still more. You can pile in more unknowns such as that CO2 dissolves in water to make carbonic acid - which increases the acidity of the oceans and adds an unknown additional risk in terms of killing off green algae - which would normally absorb CO2 and lock much of it away as ocean sediments.

Those effects are mostly non-linear in nature - the more the clathrates melt, the more the greenhouse effect pushes up temperatures, so the more clathrates melt. The more the permafrost retreats, the more greenhouse effect you get, so yet more permafrost melts. Those kinds of changes are exceedingly dangerous because once they start, we can't stop them even if we ceased adding our own CO2 to the atmosphere completely and immediately.

The bottom line here is that it is inconceivable that mankind could exist in large numbers for long enough to burn all of our fossil fuel reserves...not because those reserves are beyond what we'll ever need - but because we'd kill ourselves in the process.

The "limits" set by governments aren't to do with what's "safe" or "sane" - it's to do with what can be agreed in big international committees between governments that are being lobbied hard by oil, gas and coal producers. It's not clear that any of the limits that have been talked about are "enough".

SteveBaker (talk) 17:09, 10 August 2015 (UTC)

Coming back to what the biosphere could stand (in some form other than today)...just because bats and birds and whatever existed back when the CO2 load in the atmosphere was much higher, doesn't mean that those animals would survive if humanity pushed the CO2 load back to those levels again. The deal is that those creatures have evolved over millions of years SINCE they first appeared to take advantage of the lower CO2 levels we have today. If we suddenly push the levels back up again, they won't have time to evolve back to forms that could cope with those higher levels.

If humans added all of that CO2 gradually over a couple of million years, then I'm sure everything would work out just fine. Plants, animals - even humans - could evolve do handle the extra CO2. But we're not doing it gradually. Almost all of this change has happened in the last 100 years...and evolution just isn't that agile...especially with creatures like us with long life-cycles.

A lot of the problems are things like migratory birds flying further north in the summer to escape the heat - but the relatively sedentary insects that they feed off of only spreading north at a fraction of the speed. Over time, the insects and the birds would move north together, and everything would be OK...but if it happens too quickly, the birds run out of food and die and plagues of un-eaten insects go crazy and trash the ecosystem in some other way.

So it's FAR from clear that species that thrived in higher temperatures and greater CO2 loads than today would fare at all well if we suddenly put things back to that state over a couple of hundred years. We're throwing a wrench into an exceedingly complex machine and just kinda hoping that we don't hit anything too important along the way.

SteveBaker (talk) 17:24, 10 August 2015 (UTC)

You haven't considered all the ways the Earth will adjust to bring carbon dioxide levels back down, with northern Canada, Siberia, and eventually Greenland and even Antarctica becoming forest covered, and sucking up lots of carbon to support all that. Sure, there will be lots of coastal areas flooded, but that's not a threat to the survival of the human race. Also, in a century or two, when this becomes critical, we will have more technical capabilities to adapt, such as the ability to filter the air we breath. StuRat (talk) 18:25, 10 August 2015 (UTC)

What is the name of the tissue in the external brain?

When we look at the brain we see a vanilla color tissue, what is the name of this tissue and what is the name of the cells that it's made up of? In the article brain is written that "The brains of all species are composed primarily of two broad classes of cells: neurons and glial cells. Glial cells (also known as glia or neuroglia)" so is it Glial cells and Glial tissue? 5.28.163.245 (talk) 20:33, 8 August 2015 (UTC)

Do you mean when you're looking at a whole brain? If so, you're looking at either the gray matter on the surface, or the meninges that cover the brain. The neurons and glial cells in the brain are thoroughly intermingled. They're not separated into macroscopically distinguishable regions of neurons and glia. It's also worth noting that living brains are a deep red due to the brain's rich blood supply. Only in dead, preserved brains do you get the greyish-whitish color. --108.38.204.15 (talk) 22:37, 8 August 2015 (UTC)

Not sure, but the OP might be looking for white matter, which has a higher concentration of the myelinated axons that connect one neuron to the next. It is worth pointing out that the neurons aren't solely responsible for intelligence - in a story that I found very much creepier than some more publicized stories lately, fetal stem cells were used to make glia that effectively took over mice brains, resulting in... smarter mice. [3] Wnt (talk) 01:10, 9 August 2015 (UTC)

I agree that "white matter" is probably the correct answer. When you look at a brain with the meninges removed, white matter is mainly what you see, because it covers most of the surface. (Note that in a living brain, "white matter" is not actually white and "gray matter" is not actually gray; however gray matter is a bit darker than white matter.) Looie496 (talk) 11:39, 9 August 2015 (UTC)

Hmm, it does? The impression I get from our grey matter and white matter articles is that it's grey matter that's at the surface of the cerebrum and cerebellum. Am I missing something? --108.38.204.15 (talk) 11:53, 9 August 2015 (UTC)

Correct, grey matter is at the surface. It is true that they are fairly similar colour, thought they can be distinguished. Fgf10 (talk) 13:23, 9 August 2015 (UTC)

Power plant in Mississippi

USGS map

Dear Wikipedians,

what's the name of this (33°21′39.6″N 88°27′28.8″W) power plant in Lowndes County near Columbus, Mississippi? I can't find any information to it.--Kopiersperre (talk) 20:35, 8 August 2015 (UTC)

It's a cellulose fiber mill, part of the Weyerhaeuser company. Mikenorton (talk) 21:00, 8 August 2015 (UTC)

@Mikenorton: Thanks. With its big chimneys and the coal dumps it looked like a power station to me.--Kopiersperre (talk) 21:25, 8 August 2015 (UTC)

There's a bit more about that particular mill here. Mikenorton (talk) 21:51, 8 August 2015 (UTC)

@Mikenorton: I've just mapped that area a little bit in OpenStreetMap. Maybe the map is already rerendered.

In OSM it's quite impressive, that in the US cities are mapped very well, but factories and power plants only very vestigial. Russian factories are however covered very well: (e.g. Volzhski Pipe Factory)--Kopiersperre (talk) 22:28, 8 August 2015 (UTC)

For completeness, in case the OP actually wants to know about their local electric power generation facilities... here's a whole lot of reading material on a variety of websites! Most residents in Columbus, Mississippi get their power from either Columbus Light & Water, a Tennessee Valley Authority retail distributor; or the other major in-region electricity distributor, the 4 County Electric Power Association (also a TVA distributor). Base electric load is purchased from out-of-region via the TVA and distributed via several distribution lines; (very probably, the bulk comes from the 1.2 GW Colbert Fossil Plant in Alabama (which is actually being phased out over the next two years); and from the 3.3 GW Browns Ferry Nuclear Plant in Alabama; and during the summer, the local plant that serves that region of Mississippi is the Caledonia Combined Cycle Plant (used only when demand exceeds base load for certain periods of time). At any given instant, your power could be coming from a gas peaker, or it could be coming from a very distant TVA generating facility by way of several high-voltage distribution lines; and (during peak demands) there is a good chance it could even be coming from a non-TVA facility. There is a non-zero (but very tiny) chance that a small fraction of the energy might even be flowing from one of a handful of TVA solar facilities, or from nearby residentially-installed photovoltaic cells.

This region of Mississippi - the Golden Triangle - has an abundance of heavy industry, including steel mills, automotive manufacturers, and industrial parks, with extensive electricity needs. TVA pre-validated two "mega-sites" near Columbus to ensure that they would have access to exceptional quantities of high-availaibility, low-cost, low-risk electricity for heavy manufacturing.

Electricity generation is very complex! The energy that flows into your home is a composite of energy that can come from many interconnected parts of the electric grid, and at any particular instant, the power might be flowing from one or more of many different generation facilities, perhaps over hundreds of miles and through multiple power interconnection substations!

Nimur (talk) 03:40, 9 August 2015 (UTC)

@Nimur: Thanks for the explanation. As a Wikipedian I prefer to collect those things.

Industry in Golden Triangle:

• Steel
  • Steel Dynamics EAF 33°26′53.16″N 88°34′24.66″W
• Automotive
  • PACCAR engine plant 33°28′35.18″N 88°35′49.01″W
• Paper
  • Weyerhaeuser pulp mill 33°21′39.6″N 88°27′28.8″W

By the way, I consume European Electricity --Kopiersperre (talk) 10:16, 9 August 2015 (UTC)