Wikipedia:Reference desk/Archives/Science/2017 January 21

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.

January 21

How long ago was there a year when the global average temperature on Earth was as high as it was in 2016?

Is it likely that there existed such a year in the present interglacial or do we need to go all the way back the previous interglacial (which was quite a bit warmer than the present one) that ended 114,000 years ago? Count Iblis (talk) 00:51, 21 January 2017 (UTC)

The margin of error in the Holocene temperature reconstructions is large enough that the answer is "probably not, but we don't really know for sure." Not very satisfying but that's where we are. The likeliest time for a temperature as warm as 2016 would be the period following the rebound from the 8.2 kiloyear event. Shock Brigade Harvester Boris (talk) 00:59, 21 January 2017 (UTC)

Agreed with Shock Brigade Harvester Boris. Holocene climatic optimum has additional context. Matt Deres (talk) 14:13, 22 January 2017 (UTC)

This is a great question. First: let's clarify exactly what we mean when we say "2016 was the hottest year..."

The factoid that's been making the news in the last few days is an abbreviated brief summary of this press release: NASA, NOAA Data Show 2016 Warmest Year on Record Globally. Specifically, the GISS Model E temperature data product for 2016 enabled this statement: "NASA estimates 2016 was the warmest year with greater than 95 percent certainty."

That means we're pretty sure that this year (2016) was the hottest on record when compared to similar data compiled for all other years. This methodology can be used to compare data since 1880. When you compare within this range, the model has uncertainty and error bars. Here is one among many papers explaining the details. For example, Climate simulations for 1880–2003 with GISS modelE (2007) uses the data set to simulate climate during the range for which we also have actual measurements. This simulation includes simulation of the Model E global surface temperature anomaly. The simulation is then compared to actual data observed - so we can evaluate how accurately and precisely the model actually models climate within the range for which we have ground truth. Standard deviations are on the order of 0.2 degrees celsius, and observed average temperature rise is in the order of magnitude 0.6 degrees celsius, using this methodology - so we're in the ballpark of a three-sigma event.

Beyond 1880, extending into the distant past, we can use that same methodology - but we can't check the model against real data. Instead, we can back-project the simulation - run the model backwards! - to see what it would have predicted. The farther back we go, the greater the standard deviation - and the less confidence we can have. Think in terms of p-value: we only have a 95% confidence in the conclusion that 2016 is the warmest on record, using the data we actually have. With low confidence (!) we can make any statement we like! "With less than 5% confidence, 2016 is the warmest year in Earth's history." "With less than 5% confidence, I believe the elected leader of a major Earth government is being controlled by a shape-shifting lizard-alien." When we play linguistic games to report statistical information, we can make arbitrary statements that are absolutely factual and totally scientifically sound. Most scientists agree that a hypothesis rigorously tested to 95% confidence is "pretty solid," and most scientists agree that a hypothesis tested to less than 50% confidence is functionally worse than a "completely random guess." But hey - read any recent peer-reviewed published literature on machine learning to see how a research-community plagued by systematically-poor understanding of elementary statistics is encouraging smart humans to believe in methodologies that can only stand up to incredibly weak-confidence p-tests! State-of-the-art face recognition software can distinguish your face from a potato with near 95% confidence, which is good enough for many federally-funded law-enforcement surveillance programs! Heck, if you're ugly, a 15% performance rate is standard!

So now we have an impasse. To compare Year 2016 to paleoclimate, you need a paleoclimate model that can accurately estimate a historical GISS surface temperature at least as well as Model E. With what confidence can we actually reconstruct paleoclimate? To answer your original question, and to have a scientifically-meaningful confidence in the answer, we need a paleo-climate model whose accuracy and precision at estimating the GISS Model E temperature anomaly is better than, say, 0.2 degrees celsius (to give us that nice three-sigma event threshold). I do not know of any such paleoclimate model. This means that:

• It is very easy to find a scientist who confidently announces that 2016 is the hottest year on record (for the period 1880 to 2016)
• It is very difficult to find a scientist who confidently announces that same conclusion over a larger interval of years
• It may be impossible to find a scientist who can confidently announce the most recent year or period of years (with p-tests to 95%) during which Earth's climate was ever at this level. Our paleoclimate data sets are just not accurate enough to compare to modern GISS surface temperature accuracies; and the magnitude of the anomaly is not as large as our paleoclimate error bars.

So what do we do? Well, we share our data and our methods, and we try to make intelligent policy-decisions in the face of uncertainty. We must weigh risks.

It is my opinion that we (ecologically-minded scientists) are overly-fixated on temperature anomaly: and this is a poor strategy. People who disagree with the policies can then nitpick at the factual data; and temperature anomaly in particular has immense uncertainty. Instead, we should concentrate on something which is indisputable: pollution is bad. Let's reduce pollution! Let's reduce emissions! It doesn't even really matter if pollution causes warming, nor does it even matter how certain we are about that fact! The end-goal is to create a cleaner planet, and to reduce the ecological impact of industrial society.

...and quietly, while nobody is looking, we put better weather-cameras in space to help our next-generation researchers understand our planet with greater accuracy, resolution, and confidence.

Nimur (talk) 17:41, 23 January 2017 (UTC)

Thanks everyone for their input here. Count Iblis (talk) 02:04, 24 January 2017 (UTC)

Feynman Lectures. Lecture 44. Ch.44-5 ,Ch.44-5 Internal energy as function of something [1]

...

In doing a problem involving a given mass of some substance, the condition of the substance at any moment can be described by telling what its temperature is and what its volume is. If we know the temperature and volume of a substance, and that the pressure is some function of the temperature and volume, then we know the internal energy. One could say, “I do not want to do it that way. Tell me the temperature and the pressure, and I will tell you the volume. I can think of the volume as a function of temperature and pressure, and the internal energy as a function of temperature and pressure, and so on.”

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I, Ch. 44-5

...

Now it is interesting that besides the pressure, which is a function of the temperature and the volume, and the internal energy, which is a function of temperature and volume, we have found another quantity which is a function of the condition, i.e., the entropy of the substance.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I, Ch. 44-6

In lecture 39 [2] Feynman says that

$pV={\tfrac {2}{3}}U$
$pV=NkT$
So U is a function of T only: $U={\tfrac {3}{2}}kT$. Where is my mistake? Username160611000000 (talk) 11:51, 21 January 2017 (UTC)

You're overlooking N. --Wrongfilter (talk) 12:51, 21 January 2017 (UTC)

Yes, thank you. $U={\tfrac {3}{2}}NkT$ and mean K.E. per atom is ${\tfrac {3}{2}}kT$. But this changes nothing, as N = const , and so U~T. Username160611000000 (talk) 13:10, 21 January 2017 (UTC)

In a closed system, T is just as constant as N. To see changes, you have to open up the system, e.g. put it in contact with a heat bath to change T, or combine two systems of the same size and temperature, thus doubling N. --Wrongfilter (talk) 14:02, 21 January 2017 (UTC)

We will not consider merging the two substances to keep N = const true. And at the moment of completing Lecture 44, we know only adiabatic expansion/compression and isothermal expansion/compression. Consider isothermal expansion. Feynman says there is no change in U (see Ch. 44-4 from start to eq. 44.4). Consider adiabatic compression: $T={\tfrac {const}{V^{\gamma -1}}}$ (see remark between eq. 44.5 and eq. 44.6). So during adiabatic compression we have $U=f(T)=f(g(V))$. But this changes nothing, U is still function of temperature (even if temperature itself is a function of volume). To be a function of two variables , the quantity must contain these two variables in one equation simultaneously, i.e. $U=f(T,V)$.Username160611000000 (talk) 14:51, 21 January 2017 (UTC)

As explained here:

The expression relating changes in internal energy to changes in temperature and volume is

$dU=C_{V}dT+\left[T\left({\frac {\partial p}{\partial T}}\right)_{V}-p\right]dV$

If you use the equation of state for the ideal gas, you find that U only depends on the temperature. Count Iblis (talk) 22:24, 21 January 2017 (UTC)

Do you mean that $T{\tfrac {\partial p}{\partial T}}=T{\tfrac {\partial }{\partial T}}({\tfrac {NkT}{V}})=T{\tfrac {Nk}{V}}{\tfrac {\partial }{\partial T}}(T)={\tfrac {NkT}{V}}=p$, and so $dU=C_{V}dT$? Username160611000000 (talk) 05:28, 22 January 2017 (UTC)

Yes, so you see that the term proportional to dV drops out, so the partial derivative of U w.r.t. V at constant T is zero. Or put differently, U as a function of V when keeping T constant, is constant. Count Iblis (talk) 07:55, 22 January 2017 (UTC)

Plastic food boxes, drink cans and bottles, use water wash then recycle

Recycle bins have signs say cannot put food and drink inside recycle bins, will spoil the things for recycle. How to know what plastic food boxes, drink bottles and cans safe for recycle? Must use water wash, but use more water is bad for earth, but recycle is more good for earth? Of course boxes that not touch the food or drink are not counted. --Curious Cat On Her Last Life (talk) 12:58, 21 January 2017 (UTC)

Contact your local recycling agency to find out what their rules are. They might have a website with the rules listed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:14, 21 January 2017 (UTC)

Large amounts of the foods and drinks will cause problems, but small traces are inevitable and the recycling processes can handle them. The containers do not therefore have to be surgically clean (or even as clean as if you were going to re-use them intact), you do not therefore have to use large quantities of water for washing them. Drinks containers should be OK if they have merely been fully emptied: food containers can be adequately rinsed with, say, a quarter of their capacity's worth of water if not less, and if you do several at once you can re-use most of the water from container to container.

Incidentally, significant quantities of unconsumed food should also be disposed of in an appropriate manner, such as industrial-scale composting (which reaches sterilizing temperatures that home composting does not): my local council's refuse collection service includes bins dedicated to food waste for this purpose. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 13:55, 21 January 2017 (UTC)

See also Myth: You Must Rinse All Recyclables, Or Else! which says: "The real downside of dirty recyclables is that contaminated recycled material has less market value—which means the recycling service provider has less to spend on things like improving service and technology". Alansplodge (talk) 14:45, 21 January 2017 (UTC)

It will be cleaned and separated again and again anyway but at the begin it is usually just compacted without further processing and then traded. Ofcourse to get a good prize the initial collector tries to get the raw material as clean and preselected as he can. So it doesnt matter much if you throw in some boxes or bottles that are still half filled however if everyone would do that the first collector would have to clean and seperate instead of just compacting it to handy clusters and ofcourse he would also actually have to pay for the disposal of all the additional waste he ofcourse cant resell.

So you dont have to clean up your plastic waste befor you throw it into some recycling bin. Just make shure its as good as empty. --Kharon (talk) 00:02, 22 January 2017 (UTC)

Entering into the cost-benefit analysis of a recycling program is how much work you put on the individual customer, and how much work you put on the recycling agency. There's an inverse relationship between the amount of work you ask a customer to do and the amount of participation you get in a recyclable program. Where you require pre-sorted and pre-cleaned recyclables, the cost to the recycling provider goes down, but participation goes WAY down to; customers just throw all recyclables in with their waste, and you get very little participation. When you basically put no labor on the customer (what is often called "comingled recyclables"), that is they throw EVERYTHING recyclable, unsorted, into one big bin and don't have to do any work except remember which bin to put it in, you get MUCH better participation, but costs go up a LOT. So that weighs into the type of recycling program that an agency will set up. See here or here or here all of which cover various perspectives on recycling systems. --Jayron32 20:01, 23 January 2017 (UTC)

Convergent evolution in humans

In our artivcle Convergent evolution it says:

"When two species are similar in a particular character, evolution is defined as parallel if the ancestors were also similar, and convergent if they were not."

However, someone has recently added a well referenced paragraph that says:

"When humans migrated out of Africa, they moved to more northern latitudes with less intense sunlight. It was beneficial to them to reduce their skin pigmentation. It appears certain that there was some lightening of skin colour before European and Chinese lineages diverged, as there are some skin-lightening genetic differences that are common to both groups. However, after the lineages diverged and became genetically isolated, the skin of both groups lightened more, and that additional lightening was due to different genetic changes."

It would seem to me that the situation in humans equates to parallel evolution as the character was the same in the ancestor population, but that's clearly not the case. So how is convergent eveolution defind in a single species and can you have paralell evolution in a single species? Richerman (talk) 13:01, 21 January 2017 (UTC)

Evolution (of any sort) occurs in populations rather than species. Often, the two will effectively be the same, but in this instance the Chinese and European populations were sufficiently (though doubtless not entirely) separate that parallel evolutions (rather than a single evolution) can be considered to have occurred. This was not convergent, because although the net effect of skin lightening was much the same, it resulted from different mutations arising and being conserved, so technically different characters are involved, even though their gross visible effects are similar. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 13:38, 21 January 2017 (UTC)

That's a good point about evolution occuring in populations but the person that wrote the paragraph is a retired teacher of genetics and the reference he used is Association of the OCA2 Polymorphism His615Arg with Melanin Content in East Asian Populations: Further Evidence of Convergent Evolution of Skin Pigmentation, so it is obviously considered to be convergent. Richerman (talk) 13:48, 21 January 2017 (UTC)

Actually, thinking about it further, I would have described this instance as divergent evolution, since although the resulting appearance is roughly the same, there has actually been an increase in the genetic differences. I suppose it depends on whether your definitions are about gross appearance (which was the pre-genetic basis of anatomical comparisons) or actual genetic details. However, the editor in question and the authors of the paper are obviously qualified in this field whereas I'm only an enthusiastic fan, so I'm obviously wrong on that point. Maybe you should ping the editor and ask if the paragraph can be made clearer for us laypeople. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 14:14, 21 January 2017 (UTC)

I've discussed it a little on the talk page but not got very far yet. I was hoping for some further insights before I go back there. However, it's good to know I'm not the only one confused :-) Richerman (talk) 14:26, 21 January 2017 (UTC)

I think parallel evolution tends to be neglected. Sometimes you see "convergent or parallel". For one thing, if you don't know the exact history of the populations, it is hard to say with confidence that they had similar ancestors. Maybe one race became light-skinned first, and then the other, well, "converged" to that end point. The other argument, about how it is "really" divergent, is something that could be made in virtually every case. Convergent evolution at the molecular level is rare, though it does happen; I think red hair at MC1R is a repeated example. Nobody imagines that a fish and an ichthyosaur have more similar genes than the ancestors of the two did. Convergent is defined for a specific endpoint, and no other - the fins might converge, the bones of the skull not so much. Wnt (talk) 15:08, 21 January 2017 (UTC)

• It would be wrong to make too much of this. The distinction between parallel evolution and convergent evolution is not something that most geneticists pay a lot of attention to -- they tend to use the term "convergent evolution" for both. Even among scientists imprecision in terminology is pretty common. Looie496 (talk) 14:10, 23 January 2017 (UTC)

Medical apparatus

Does a medical apparatus exist for measuring the amount of human flatus pruduced and the number of flatal(?) events. I ask because medical web sites quote figures for quantity and number of daily emissions. --31.121.94.188 (talk) 18:59, 21 January 2017 (UTC)

• I have not looked at all of them, but there are quite a few medical papers in the references of Flatulence, one of which may contain information of the protocol. (Even then, such devices might not be commercially available, but that is a lead.) Tigraan^{Click here to contact me} 19:06, 21 January 2017 (UTC)

• I believe there is a rarely used device called a flatus bag/flatal bag, which was designed to collect samples. Analysis of the flatus gases could theoretically be useful in diagnosis of digestive system diseases, but other diagnosis techniques, such as a stool sample, seem to be easier to collect and more effective. StuRat (talk) 01:33, 22 January 2017 (UTC)

See "What is a rectal tube (or catheter)" illustrated, with discussion and "Use of flatus tube." Blooteuth (talk) 15:05, 22 January 2017 (UTC)

The contents of flatulence are commonly measured indirectly by blood sample. Only when there is a concern for a specific problem will a direct measurement be made. However, that is usually skipped over as an examination of the problem causing unusual flatulence may be easier to check than attempting to capture and analyze flatulence. I've only known two cases of a blood test for flatulence being performed in over 20 years. I've never known of a flatulence bag being used to capture flatulence, but I know it exists. First, I don't work in GI and most intestinal problems are checked using stool specimins, MRI, colonoscopy, or ultrasound. Flatulence is not a primary diagnosis tool. On a related note, I do remember a study on bovine flatulence that used flatulence bags. 209.149.113.5 (talk) 12:43, 23 January 2017 (UTC)

Flatus bag is a bluelink. DMacks (talk) 13:40, 23 January 2017 (UTC)