Tuesday, 22 September 2009

• Global Warming Explained

  
  The following is my best attempt to explain the basics about global warming
  
  
  

  An exponential problem
  

  
  During the last century, we averaged .07 degrees C warmer per decade (which lept to .13 degrees in the last 50 years). There is little doubt that our planet is warming even amongst global warming deniers - the question is about what is responsible for it.
  
  Our concern should be that even a little bit of warming exacerbates the problem in terms of CO2 (carbon dioxide). This is because CO2 does not function in water the same way most molecules do. Most molecules are more soluble in warmer water, but CO2 is less soluble in warm water. This means that by even increasing the temperature a little bit, we are reducing the ability of our oceans to hold CO2. This creates a positive feedback situation with our atmosphere that begins a self-perpetuating cycle in which the CO2 not absorbed by our oceans helps our atmosphere to trap more heat, which causes the oceans to be able to hold less CO2, so on and so forth. The figures atop this paragraph represent that little bit of warming that will catalyze an exponential increase in temperature in the troposphere (where we live).
  
  For more on this, read here.
  
  So, how much are we contributing to this? First, see this graph.
  
  That is how much we are augmenting the problem. Remember, even a little increase creates an exponential increase, and it's clear that such an increase is precisely what we have. We can cross reference the above research through a variety of methods such as examining the CO2 inferred from polar ice cores.  There are several ways we can go about establishing where our CO2 totals are now in comparison to in the past and, again, even global warming deniers like John Coleman do not deny that CO2 totals have spiked since the industrial revolution, they are just arguing that it doesn't matter.  Though I wish people like Coleman were correct, all the evidence strongly indicates they are not.
  
  We can very accurately measure the ppm (parts per million) of CO2 in the atmosphere, and we have gone from a pre-industrial average of 280 ppm to 385 now (and this trend is continuing). The only way somebody could shrug this off is if that addition 105 average ppm didn't make a difference.  Recall the effect of CO2 on oceans, and they're ability to dissolve CO2.  That is one reason why the data cannot be ignored here, but there are certainly others, and they will make up the bulk of this entry.
  
  Before we go forward, I must point out that it's really not important that you understand any portion of this subject (or that I understand all of it which, allow me to assure you, I do not).  All that is important is that the experts do understand it.  They have dedicated their lives to this, and understand it better than anybody else on the planet. That is why they are in consensus, and it is the reason that people like John Coleman, non-scientists masquerading as experts, are not present in peer-review - their arguments would simply never survive it.  I simply make this available for those who do with to try and understand the subject more deeply, which is to be commended.
  
  There is simply too much information within the human knowledge base right now to learn in several lifetimes.  We can never learn everything about everything, or even most of what there is to know about everything.  Even the most well-informed human will still be ignorant of almost everything there is to know.  In order to have a full, reasonable world view, we must defer to experts on various subjects.  The problem is that most people have a very poor methodology for determining who the experts are.  This allows people to think that non-experts like John Coleman are more reliable than the consensus of climatologists churning out peer-review literature on the subject, or that their favorite priest has information about the cosmos that no cosmologist has.
  
  Moreover, peer-review scientific literature is complicated stuff.  They use a great deal of jargon and are difficult for laymen to even come close to grasping.  This is not to imply that laymen are more or less clever than scientists, just less trained and, hence, possessing less expertise.  Sadly, this is the very evolved arena in which the discussion for what gets to be scientific fact occurs.  If you want to know precisely what the experts say, you have to go to this literature, and this would require far more work than almost any non-scientist could reasonably be expected to put in.  Again, we must defer to experts.
  
  By any sane measure, it is clear that climatologists are in near harmony that man-made gasses are warming our planet unnaturally and dangerously - and that the process is exponential.  Moreover, every major scientific body is in consensus on the subject as well.  These are the experts.  The problem is that laymen who claim to have the evidence to overturn scientific fact on the matter are disseminating their ideas to the public, without scrutiny, rather than submitting their work to journals and receiving credit it for it (and affecting the policy of several governments in how they address, or decline to address, the problem).  The greater problem is that other laymen, passionate to the fullest about the issues, listen to them.
  
  

  Physics
  

  
  How do we determine if man is contributing to global warming?  What is our methodology?  Is it just a guess?  How certain can we be?
  
  There are several concepts we'll need to become acquainted with before we take a look at the physics of global temperature.  I realize that a lot of this can get pretty confusing.  I am trying to use as much colloquial language as possible.  Send me a message if you have questions and I will do my best to get back to you and help you understand.
  
  1.  Blackbody radiation
  
  To quote the wikipedia:
  
  

  At room temperature, black bodies emit mostly infrared wavelengths, but as the temperature increases past a few hundred degrees Celsius, black bodies start to emit visible wavelengths, appearing red, orange, yellow, white, and blue with increasing temperature. By the time an object is white, it is emitting substantial ultraviolet radiation.
  
  

  Blackbodies are "perfect radiators."  They produce idealized light emission from a heated object.  They are perfect radiators and absorbers of energy at all wavelengths.
  
  2.  Planck's Radiation Law
  
  Planck's Law deals with emission vs. wavelength at a particular temperature. 
  
  

  
  
  

  We use this to track energy emission from a heated surface per square meter per micron.  This is expressed mathemagically as J s^-2 * m^-2 * um^-1 = W * m^-2 * um ^-1.  If you follow the link to the wikipedia, there's a whole chart talking about what all those funky letters mean.
  

  
  3.  The Wien Displacement Law
  
  Wien's Displacement Law is the first  derivative of Planck's Law.  It provides us with the peak emission for a specified temperature.  It can be simply expressed as follows:
  
  

  
  

  
  4.  Stefan-Boltzman Law
  
  This is the integral of Planck's Law.  This gives us our total emission intensity for a specified temperature.
  
  

  
  

  
  So, let's start with Solar Irradiance. The surface of the sun runs at about 5,780K - this all must get distributed to our planet somehow. We determine this by using Planck's Law:
  
  

  (5.67 * 10^-8 Js^-1 m^-2 K^-4)(5,780K)^4
  = 6.3 * 10^7 Js^-1 M^-2
  = 63 MW per M^2

  We can also find the peak wavelength we receive from the sun via the Wien Displacement Law:
  

  Wavelength (in um [microns]) = 2,898um * K/5,780k = .501um = 501nm

  These numbers will come in handy shortly.
  
  Now, the total amount of energy reaching our outer atmosphere is 1,370 Wm^2. From this, we derive two different figures.
  
  

  1. The energy delivered to our cross section (pi * r^2)
  2. Total amount dispersed over Earth's surface area (4 * pi * r^2)
  

  
  The total of 1 divided by the total of 2 should give us the average energy reaching our outer atmosphere. This comes out to 342 Wm^2.
  
  Now, go back to blackbody radiation - this is how the Earth works. If the Earth had no atmosphere, it would absorb 342 Wm^2. What temperature would this predict, that would radiate that same amount of power?
  

  342W/m^2 = (5.67 * 10^-8 * w/m^2K^4)T^4
  T = 279K or about 6 degrees celsius.

  This is pretty damn cold, so something must be missing (pirates, I tell you, yaaaarrrrrr!).
  
  What's missing is the Earth's Albedo. This encompasses what solar irradiance gets reflected from things like clouds, ice caps, water bodies, light colored land, etc. For the Earth, our Albedo is about 30% of solar irradiance.
  
  Figuring out how much energy reaches our surface is pretty easy after we have our Albedo. It's Solar irradiance * (1 - a), with "a" being our Albedo, which comes out to about 240 Wm^-2. So to attain a stable temperature we need to balance incoming energy with emitted energy. The 240 Wm^-2 in, must be balanced by 240 Wm^-2 out via blackbody radiation of the Earth's surface. 
  
  We can use the Stefan-Boltzman Law to determine what surface temperature we would expect to find in this case. 
  

  T ={ [240 Wm^-2] / [5.67 * 10^-8 Wm^-2 * K^-4]}^-1/4
  

  This comes out to be 255K (or -18 degrees C), but we observe the average temperature of the Earth to be about 15 degrees C. This predicts 390Wm^-2. How can this be?
  
  It's because about 150Wm^-2 never escapes back into space. It gets absorbed by the atmosphere and re-emitted to the surface. The primary variable in this is greenhouse gasses.  This is the variable that matters in regards to how much C02 we're pumping into our atmosphere.
  
  Before I go on, I'll stop to say that I hope you're getting a feel now for how science is not simply a matter of guesses. It is a very precise process of using what we know to wrest our circumstances from a mute nature.
  
  

  Other threats
  
  

  In reading the following section, you may be tempted to think of these gasses as pollutants which, as frauds like John Coleman are quick to point out, is not true.  We need these gasses to get along.  Even CO2 is not a pollutant.  Plants need it to produce the oxygen we breath.  However, as we saw in the physics section, it's all about creating a balance.  It is only when we throw the balance out of whack that things get messy.  Once we start producing gasses beyond the natural threshold, then they become pollutants.
  
  Moving past that, there are other threats other than CO2 to global warming, in which mankind has a hand.  There are three key gasses that play a part here, they are CH4 (methane), N2O (nitrous oxide...wheeeee!), and O3 (ozone).  All of these have a pound-per-pound ability to trap energy compared to CO2 that has been assessed by the scientific community.  The epa has a very informative page explaining these things in far greater detail than I'm about to.
  
  1.  Methane
  
  Methane is certainly on the rise.
  
  

  
  

  
  The increase in atmospheric concentrations of methane are due to mining, grazing, and other related activities, many due to the industrial development of human beings.  Methane has a very strong absorption pattern in the atmospheric window and, pound-for-pound, has an energy-trapping potential about 21 times that of CO2.  On top of that, there is a great deal of methane hydrate incorporated into ice structures all across the Earth, such as permafrost and underwater deposits.  A thaw of those structures could release enormous amounts of CH4.  For this reason, it is the most important gas to monitor after CO2, since CO2 is far more plentiful, has a greater impact due to its larger volume, and would provide the means for the warming that could release the methane.
  
  2.  Nitrous oxide
  
  We've seen a slow increase in N2O ever since the 1950s.  Various lines of evidence suggest about a 16% increase since 1750, and about a .25% annual increase for the last 20 years.  This increase has come primarily from natural sources, with a small amount coming from
  
  N2O has a very high global warming potential, about 310 times that of CO2 (the wikipedia page says it has 298 times the impact of CO2, but my textbook says 310.  Going with the book.).  However, it is so limited, and the rate of increase so small, that it does not overtake methane on our list of threats.
  
  3.  Ozone
  
  I'll spare you the detailed explanation, but suffice that ozone is very, very difficult to work with, and it is hard to assess its overall role in global warming.  Ozone in the stratosphere actually cools that portion of our atmosphere.  However, in the troposphere, the part we live in, it warms things.  That divide is the reason that as the Earth warms, we will see more violent weather.  Don't get me wrong, I love thunderstorms, but not all the time.
  
  On the whole, we know that ozone produces a net warming effect, but it is very mild compared to all the other gasses.
  
  4.  Others
  
  There are other trace compounds that serve as potential future threats to warming.  HFC-23, for instance, has an atmospheric life of 264 years and a global warming potential 11,700 times that of CO2.  HFC-134a has an atmospheric life of 14.6 years and a global warming potential 1,300 times that of CO2.  CF4 has an atmospheric lifetime of 50,000 years and a global warming potential 6,500 times that of CO2.  C2F6 has an atmospheric lifetime of 10,000 years and a global warming potential 9,200 times that of CO2.
  
  Thankfully, these substances have been reigned in by governmental action.
  
  

  Objections
  
  

  There are some objections to the scientific consensus, some of them coming from reputable scientists.  Here, I will answer them as they come up.
  
  1.  Solar forcing
  
  The Sun's energy output is not constant.  The Sun goes through various cycles of higher and lower energy output.  Most importantly amongst them are the Schwabe cycles and the Milankovitch cycles.  The issue in question is whether or not these phenomena are what is responsible for all the irregularities we've detected in the data over the last 70 years.  An argument in favor of these cycles being the cause of recent warming exists in the peer review literature, so this is not a fringe position, even if it is not the one almost universally adopted by climatologists.
  
  The article was published in 1991 and since that time, the argument has become less convincing.  When scientists produce graphs to explain their results, they filter the data to smooth out the image by accounting for background variation and anomalies.  The paper in question did this for all of the data except for the last part, because they did not have all of the information required to actually do it.  When the data became available, the end of the graph told a completely different story:
  
  

  
  
  

  The correct graph displays a side-by-side relationship between sun cycles and temperature for the last 260 years, but not recently.  Recently, global temperatures have risen while solar activity has remained essentially constant.  The work of Christensen and Lassen, with updated information, corroborates the notion of carbon emissions playing the main role in unnaturally increasing global temperature.  Several papers have followed since 1991, and all of them confirm this.
  
  At this time, solar forcing does not explain the recent spike in warming.
  
  2.  Water vapor
  
  Another oft-cited objection to the data by climate change deniers (a group that is virtually unrepresented amongst climatologists) arose from the scientific community way back in 1930s, when the problem of carbon emissions was in its infancy as far as being a scientific question.  The perfectly factual objection was that water vapor also traps CO2, and it is far more plentiful.  This is true, but incomplete.
  
  Many scientists in the 1930s noted that water vapor also traps radiation, and that it is far more plentiful than man-made carbon emissions.  They also pointed out that the Earth goes through cycles of high CO2 production.  This fact is why experts were unconcerned with the spikes in man-made CO2. The experts at that time assumed there would be a balancing mechanism that would set everything straight (this would later be branded the "Infrared Iris Hypothesis" in the 1990s).  Ice core data confirmed these cycles:
  
  

  
  

  
  The major problem here is that spike there at the very, very end, which mirrors that of Christensen and Lassen's corrected solar forcing graph.  Our previous high spike was about 290 ppm of CO2, yet we're currently at an average of 385 ppm.  What's more, we should be in a decline right now, the beginning of which you can see before the rise of humanity on the time line.  We are now way outside our normal pattern.
  
  There is more to the water vapor story.  In 1941 an engineer named Guy Stewart Callendar figured out that water vapor and carbon dioxide block in radiation at different wavelengths.  Water vapor absorbs radiation from 18-30 um, while CO2 absorbs radiation in the 8 to 18 um band.  This compounds the heating effect of water vapor, and plugs a means by which a great deal of infrared radiation escapes back out into space around the water vapor band.
  
  

  
  

  
  
  It was then that the scientific consensus began to change, and it has done so for the last seventy years.  The fact that lay people who are averse to the idea of global warming, for whatever motivation, still continue to use this argument is a testament to our inability to rightly determine the experts on a subject.

  
  

  Outro
  
  

  There is, of course, more to the story.  The physics above only deals with the bare-minimum, and does not deal with positive feedback from water vapor, negative feedback from increased cloud cover (or even the distinctions in clouds, such as cold nature of poor radiator high clouds versus the warmer, better radiator low clouds), or the physics of aerosols.  Since, as I do with most serious things I write here, I will be copying/pasting from this or linking to it frequently, it is possible I may have to add those things in at some point.  If the need arises, I will.
  
  I should also take a moment to point out that it should be clear in this case that we cannot make science say whatever we want. Science points directly, and unequivocally, to very specific conclusions.  I say this because I am composing this primarily as a response to somebody who asserted that we could, in fact, make science say whatever we want.  Everything that is reasonable to believe about the nature of reality has been revealed to us through science.  It is the reason we have abundant food, clean water, fast travel, medical treatment, and every luxury that makes life in this generation a veritable utopia compared to those before it.  Choose your experts wisely.
  
  It's our planet, and we don't get another one.
  

  
  

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