It's land use

Comments 1 to 12:

1. johnd at 18:56 PM on 4 April, 2010
   I'm just following from a discussion on the "A residential lifetime" thread as it was getting off topic over there. That discussion centred on the residential lifetime of atmospheric CO2 and the fact that 3.3 Gt of CO2 was being added to the atmosphere each year..... Various industry and government reports generally put the global annual production of cement in the vicinity of 3 Gt which translates into about 10 Gt of concrete. Most of this concrete results in new structures being built on the earths surface and provide a substantial thermal mass, absorbing and then dissipating heat energy. Apart from the quantity produced each year compared to CO2, and the ability to absorb and then radiate heat energy as does CO2, the residential lifetime of concrete structures most likely exceeds that of CO2 given that the recycling of concrete is likely far less than that of CO2 within the carbon cycle. If 3.3 Gt of a gas being added to the atmosphere is of concern, then should 10 Gt of a high thermal mass product also not only be of concern but have a measurable effect.
2. doug_bostrom at 04:46 AM on 5 April, 2010
   JohnD it's probably helpful to remember that production of cement is itself a significant source of C02.
   
   Calcination of cement during manufacture liberates C02, offset to some extent as cement ages after use and reabsorbs C02, but this takes a very long time indeed so calcination of newly made cement remains a significant net contributor to our C02 emissions. The manufacturing process is also inherently energy intensive, itself responsible for consumption of large quantities of fossil fuels as the components of cement are heated.
   
   In the U.S. cement production is responsible for something like 10% of C02 emissions.
   
   As to heat capacity of cement, needless to say the raw materials used in production of cement are not imported from off-planet; the mass of the Earth does not change when a kilogram of cement is created and thus the notion that all the cement we manufacture is going to be a net sink of for heat is an error.
   
   Regarding the radiation of heat from cement structures, they of course share with everything else on the surface of the planet the requirement for whatever energy they do radiate to penetrate the atmosphere and escape, which is of course the main problem we're facing with the ever more fluffy and cozy blanket we're making with our C02 emissions.
   
   There are some schemes currently in play to sequester C02 from coal plants in cement but they do not at this time appear suitable for massive deployment due to shortages of alkaline compounds needed in the diversion process as well as disposal problems with acid byproducts.
3. johnd at 05:34 AM on 5 April, 2010
   Doug, whilst the mass may not change due to concrete production, the surface area exposed to the atmosphere does so dramatically. Soil temperatures just slightly below the surface remain fairly constant, and depending how deep you go start to get warmer. However when the raw materials are mined and finally erected as concrete with large surface areas and relatively thin sections there is a massive increase in the thermal mass exposed to the atmosphere which through heat absorption and then slow release must have some measurable effect. If 750 Gt of a minor gas in the atmosphere becomes a concern when 3.3 Gt extra is added annually to the atmosphere, what effect does adding 10 Gt of concrete to what is an already massive amount already in place. What I trying to understand is given the ability of a gas such as CO2 to absorb and re-radiate thermal energy is somewhat less than those solid materials considered to provide efficient thermal mass properties, can the much larger quantities of concrete be ignored, especially given the large increase in surface area exposed to the atmosphere.
4. doug_bostrom at 06:08 AM on 5 April, 2010
   JohnD, it's the sky-facing radiator of the Earth's surface that is significant in the way you describe, and it's going to remain the essentially the same regardless of whether it's covered with buildings, deserts or trees. We can't significantly increase the sky-facing area of the Earth, or at least we have not figure out how to do that yet. The absorption/emissivity characteristics of various materials do vary but I wouldn't care to guess whether concrete is a better radiator overall than shrubbery.
   
   The mass of the C02 added to the atmosphere is a way of measuring the amount in play but likening the heat capacity of that mass to that of a mass of concrete is not a useful way of thinking about the situation. The issue here is not the amount of heat that C02 will absorb, but rather its effect on the escape of thermal radiation from the atmosphere. Whatever is at the bottom of the atmosphere be it mesas or urban monads, the radiation they emit must wend its way through the air column and escape into space. Relative mass has nothing to do with the problem.
   
   I suggest you do some back of the envelope calculations to get a grasp of the amount of energy arriving at the Earth's surface versus the heat capacity of the quantity of concrete you're speaking of. The numbers here are way beyond intuitive.
5. doug_bostrom at 07:09 AM on 5 April, 2010
   By the way, I should mention there's a fun experiment possible for investigating what JohnD and I are discussing here, one that can be done pretty cheaply at home.
   
   You'll need two small concrete slabs and two thermometers with the bulb or thermistor arranged such that they can be brought into contact with a surface.
   
   --If you don't have some at hand, go to your garden supply center and buy a couple of concrete slabs of the type used to make walkways and the like, 12"x12" or similar.
   
   --Attach a thermometer to each slab, making sure the thermometer bulb or thermistor is in good contact with the slab.
   
   --Now arrange one slab so that it is parallel to the sky, the other perpendicular to the sky.
   
   --Wait for a clear night. A few hours after dark, take a reading from each thermometer. The sky-facing slab will produce a cooler reading.
   
   --Wait for a cloudy night. Again, a few hours after dark take a reading from each thermometer. The disparity between the readings will be less.
   
   A neat little demonstration, with various possibilities for further experimentation.
6. johnd at 07:15 AM on 6 April, 2010
   Doug, I don't want to turn a fun experiment into a full blown project, but to get the most out of such an exercise, the temperature of the slabs would have to be tracked at least a full 24 hours with an additional slab stood at right angles to the other standing slab, as well as the temperature being recorded just below the soil surface over the same period. One of the objectives I believe is to measure under what conditions any residual heat will remain after a full day/night cycle. Of course what matters really is what heat remains after a full summer/winter cycle.
7. johnd at 07:29 AM on 6 April, 2010
   Doug @4. I believe that if the infrastructure humans build creates additional thermal mass that stores heat that otherwise would radiate off at a faster rate, then that does alter the immediate environment we live in. This is something we all know, what a relief to escape the stifling city heat during the warmer days, or nights....With regards to the UHI effect, there are 2 aspects to it. The first is what effect it has on the natural climate. The second is what effect it has on the data collected that is used to quantify the physical conditions. I am not certain that the scientists have got a handle on the second as yet. Certainly revelations in recent times have created a considerable amount of doubt.
8. doug_bostrom at 07:43 AM on 6 April, 2010
   The answer for your #6 is easy, johnd. With steadily improving insulation the Earth's retained heat will increase, until the planet reaches thermal equilibrium again.
   
   This whole issue is really not complicated in its essential features but the scale of the phenomena involved defies our intuitive numeracy.
9. doug_bostrom at 07:52 AM on 6 April, 2010
   BTW, johnd, what doubts do you harbor about what you term "revelations" concerning the UHI effect?
10. aj1983 at 22:14 PM on 12 April, 2010
    This topic has been a bit weak of a defence for the allegations that the trends above land (and global trends) are significantly influenced by UHI AND other non greenhouse gas influences.
    
    I think it would be nice for the climate science community to look into this more seriously, because there is an increasing amount of literature pointing into the opposite direction.
11. jdaviescoates at 18:30 PM on 4 August, 2010
    From one perspective "land use" can be seen to include everything we do that generates CO2 (how we grow food on land, how we mine minerals from land, how we transport over land, how we live on land etc etc.)
    
    If "land use" is analogous to "how we live on planet Earth" of course its land use.
12. muoncounter at 04:54 AM on 13 October, 2011
    Continuing from here
    
    
    --source
    
    This document (written in 2002) suggests that forested area in the US is recovering slightly:
    
    Forest land area increased from 747 to 749 million acres (0.3 percent) between 1997 and 2002, continuing a slight upward trend in area beginning in the late 1980s.
    
    Since the bulk of the deforestation occurred in the 19th century, this cannot be a significant contributor to recent warming.

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