Sunday, April 22, 2012

Determining Causes of Global Warming

  The Village Elliot continues to be interested in the science of global warming.  In fact, we all need to be interested in this because what we believe about global warming has a strong influence on what we do concerning processes (mainly involving energy) that increase the amount of carbon dioxide in the air.  
    It seems to me that the data of the 20th Century is rather good, especially after beginning of the satellite age. There is a huge amount of debate about the way some of the data has been presented, and I think you can legitimately get wrapped up in issues surrounding accuracy and ethical analysis, but at the end of the day it is pretty much a fact that the global average temperature has in fact increased since the start of the 20th century.  The global average temperature as estimated by the National Center for Climatic Change has risen by about 1.0 degrees Celsius, beginning in about 1908.
    Second, there is no doubt that carbon dioxide absorbs infrared radiation.  In fact many people point to the data from Mauna Loa as one of the best documented records of the actual CO2 data (these records were accumulated by the United States Air Force.  Nobody bothers to ask why the Air Force does such things, but there was a very practical reason.  The Air Force was--and is--very interested in using lasers for communications and other reasons.  We had to know whether lasers such as CO2 would be able to propagate in the atmosphere.  In fact, when I was a Second Lieutenant, I was assigned to a group that worked on lasers, and the fellow next to me helped to develop computer codes based on data from the Maui observatory).  
Hence there is no real reason to doubt that carbon dioxide is a warming influence.  If global warming were a murder mystery then, CO2 might be considered a prime suspect.  But why not check for fingerprints?

It turns out carbon dioxide, as we well as other known mechanisms of global temperature change have other scientifically observable signatures.   For example, carbon dioxide acts to insulate the earth's surface, reducing the loss of infrared radiation.  This means, other things being equal (and of course they never are, but please bear with me):

   1.  Nights should show more evidence of warming than days, and that the cooldown rate after sundown should be slower than it was years ago, 

   2.  Winters should show more warming than summers;

   3.  The night/day (diurnal) and seasonal effects should be observed all around the world, including both the northern and southern hemisphere;

  4.  Central Antarctica (not the coastal regions) should be the best place to make an unambiguous measurement, since it is so cold that there is very little water vapor to interfere with the measurements.

   5.  The effect should be present in both land and sea surface temperatures.  

    I think that there are other effects that are also present, and the importance of each of these effects is still a subject of study. 

   Global dimming (or undimming) is another effect, but which has a much different signature than carbon dioxide warming.  Global dimming is the result of particulate emissions from human pollution (i.e., like smog), which blocks the transmission of sunlight. This has the effect of cooling things in the daytime when the sun is shining brightly.   You expect this to occur mainly near highly populated areas, and not necessarily out in the middle of the ocean or in the Southern Hemisphere of the earth where there are fewer people. Global undimming is the opposite, which might have been observed when people started to scrub the emissions from power plants and steel mills, for example.  If the planet were covered by smog and then suddenly began to be cleaner, then there might be some warming that could be observed, mainly in the daytime, and more strongly in the summer since there is more sun in the summer.  Global dimming would result in cooler peak temperatures during the day, but not much effect at night.  Global dimming would not have much effect in Antarctica in winter
   Hence there should be a good chance of being able to discriminate between CO2 greenhouse effect and global undimming.
   Perhaps now the reader will get the general idea of what I am proposing.  Rather than simply wait 100 years to see if any of the CO2 global warming predictions come true, the scientific community should be coming up with other tests and diagnostics to see what effects are actually present.  In other words, we should test the computer models.  This is standard science in every other field.  You make predictions and explain what measurements would tend to support the model and what measurements would tend to cast doubt on the model.  This kind of analysis does go on in the literature, but at a greatly reduced level compared to what should be going on.  Most researchers are content to make predictions that can not be tested until after the current generation of scientists, and then it will be left to our grandchildren to judge the predictions made at turn of the our century. 

  The table below lists some of the observations that might be made about the climate, along with the different effects.  
  I have also made a tentative assessement about whether the effect would be observed or not, depending upon the cause.  
   Conventional climatologists would probably say that CO2-induced greenhouse effect is the primary cause of 20th century global warming, along with feedback effects such as ice coverage and water vapor.  
   That is, when the climate warms, the amount of ice coverage is reduced.  Ice is reflective of solar radiation, whereas land or water is more absorptive.  That means the earth will absorb more heat, which melts more ice, which causes more heat absorption, and so on.  That is referred to as a "positive thermal feedback."  Similarly, when the climate warms, this increases the humidity.  Water vapor is also an infrared absorber, so increased humidity results in increased warming and so on.  Both of these effects are thought to be present along with carbon dioxide effects, and in fact the feedback effects are necessary in order to interpret the stronger warming that has been observed in the Arctic and to a lesser effect than the Antarctic. 
   Other possible contributors to global temperature change might include:

      a.   an optical darkening of the ocean, which could occur if algae proliferate due to the increased presence of fertilizer chemicals, which would cause increased absorption of sunlight, but not so much on the land; 
     b.  darkening of the surface of snow and ice due to the presence of soot, possibly from air pollution, which would cause increased absorption of sunlight (thus warmer days, but little or no effect on night temperatures).

    c.  Changes in cloud cover, which depending on the form of the clouds might change the amount of sunlight reflected from the earth.  Hence reduction in reflective clouds might lead to an increase in daytime temperature;

     d.  Natural cycles, such as the Artic Oscillation (AO), North Atlantic Oscillation (NAO), El Nino, La Nina, Pacific Decadal Oscillation, etc. are also know to have some effect on global temperatures, both up and down.  

    e.  In addition to the proposed mechanisms shown, there are any number of other explanations offered in the scientific community.  The NASA GISS website lists some of the main forcings that the community deems to be credible, along with an estimate of the magnitude of their effect.  

Effect CO2 GW Global undimming Darkening of the ocean Darkening of the snow Reflective cloud cover Natural cycles Ice coverage feedback water vapor feedback

Overall warming yes yes yes yes yes Maybe yes yes
More warming in north hemisphere No Yes No yes no Maybe
More land warming than ocean warming No Yes No Yes No Maybe Yes No
More polar warming than low lattitudes Yes No No Yes No Maybe  Yes Yes
More daytime warming No Yes Yes Yes Yes No Yes No
Antarctic winter warming Yes No No No No Maybe No No
More night warming Yes No No No No No No Yes

    The simple "yes" and "no" responses in the above table are tentative, and you might argue about the exact effects that should be observed. But the point is that each of these observables should be measured and analyzed to see if they are consistent with the model or not.
  Probably each analysis is worth at least a PhD dissertation, and an estimate should be made about how large an effect is expected versus how much is actually measured, with all sorts of qualifiers.  For example, some people have worried about the failure of central Antarctica to behave as the model predicts, and perhaps there is some other effect involving the earth's ozone layer that is able to overpower the effect of just CO2.  
   At some point, the Village Elliot hopes to compile the overall analysis in a monograph, which might be some 100 pages long.  That's too much reading for this blog.  So instead I will publish it bit by bit.  

       But for the moment, like the bumbling detective in the murder mystery, I haven't said whether the primary suspect (namely carbon dioxide) is really guilty or not.  After all, questioning global warming is perceived by some as a foolish exercise, akin to helping O. J. Simpson search for the true killer.  Nevertheless, my heretical opinion is that the evidence does not lead to carbon dioxide, or at least not exclusively so.

For additional reading:

An excellent source of information about climate issues related to global warming, imho, is contained in the Proceedings of the Second International Conference on Global Warming and the Next Ice Age.  I don't know why there has not yet been a Third conference, maybe due to political heat.  Anyway, you can find a summary at this link, including a mention of yours truly's paper:

Climate forcings that NASA accepts as real, along with a discussion of their relative importance are summarized here:

Discussion of global dimming and undimming may be found at 
Gerald Stanhill, Shabtai Cohen, Globaldimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences, Agricultural and Forest Meteorology, Volume 107, Issue 4, 19 April 2001, Pages 255–278

David G. Streets, Ye Wu, Mian Chin, Two-decadal aerosol trends as a likely explanation of the global dimming/brightening transition, GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L15806, 4 PP., 2006

Discussion of the darkening of polar ice is discussed by 

Mark Z. Jacobson, Climate response of fossil fuel and biofuel soot, accounting for soot's feedback to snow and sea ice albedo and emissivity, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D21201, 15 PP., 2004

The effect of ozone on Antarctica, which otherwise is the clearest opportunity to analyze CO2 without interference from water vapor:  

Judith Perlwitz et al.,  The Impact of Stratospheric Ozone Hole Recovery on Antarctic Climate, Geophysics Research Letters, 2008.

P. D. Jones et al., Surface air temperature and its changes over the past 150 years REVIEWS OF GEOPHYSICS, VOL. 37, NO. 2, PP. 173-199, 1999

Kushner, Paul J., Isaac M. Held, Thomas L. Delworth, 2001: Southern Hemisphere Atmospheric Circulation Response to Global Warming. J. Climate, 14, 2238–2249.

The diurnal change is discussed by NASA's Hansen, from back in the day:

J. Hansen,    M. Sato, and R. Ruedy, Long-term changes of the diurnal temperature cycle: implications about mechanisms of global climate change, Atmospheric Research, Volume 37, Issues 1–3, July 1995, Pages 175–209.

M. J. Filipiak, C. J. Merchant, H. Kettle1, and P. Le Borgne, An empirical model for the statistics of sea surface diurnal warming, Ocean Sci., 8, 197–209, 2012
..with a cautionary note:

Steven C. Sherwood,    John R. Lanzante, and Cathryn L. Meyer, Radiosonde Daytime Biases and Late-20th Century Warming,  Published Online August 11 2005
Science 2 September 2005: Vol. 309 no. 5740 pp. 1556-1559

Sarah M. Kang, Croll Revisited:  Why is the Northern Hemisphere Warmer than the Southern Hemisphere? J. Climate,

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