Climate change (Class of 2019): follow-up lecture

This page was written to be shown during the follow-up lecture on 8 Aug. 2019. So, the text is not (yet) finished as a written text.

Section 1 of the term report assignment

This is a very crude example of "projections" of climate in the future. Please do not consider this as projections to be used in real policy-making. I wanted you to be accustomed to our (climate scientists') way-of-thinking.

There are a lot of uncertainties, but it does not mean that we know nothing. The human society must make decisions under this kind of situations.

Concentration scenarios: A (crude) measure of how climate can be different according to choice of policies regards to CO₂ emission.

Others: Some measures of uncertainties of scientific knowledge about the climate system.

• Steady-state response (SSR) of temperature to CO₂ doubling: A measure of sensitivity of the climate system to radiative forcing. (This type of sensitivity is based on long-time average input and output. It does not involve the question of how fast the response will be.) The larger the SSR, the larger the actual response.
• Depth of the layer of water: A measure of time scale dependence of the response of the climate system. The larger the depth, the smaller the transient response, but, in the long run, there will be a large effect.
• Coefficient of relaxation: Another source of uncertainty about the climate system appearing in this particular formulation of the energy-balance climate model. (Some other parameters will exist in much sophisticated models which are used by experts.)

Notes about computer software [added 2019-Aug-12]

This kind of simulation can be done with spreadsheet software, as some of you tried successfully. I do not recommend spreadsheets for serious use of this kind, however, because it will be difficult to avoid mistakes and to make the processes of analysis traceable.

In this class, I showed an example program in R. R is a special-purpose programming language for statistical data analysis.

It seems to be better to use general-purpose programming languages. One candidate, contemporary popular, is "Python".

I used R, partly because I wanted to use graphics capabilities of R. I am sorry I showed just an example of very crude numerical ourput of the result. I should show examples of graphical output, and also numerical output in good formats for re-use, but I could not create them in time. Parhaps I add some examples later somewhere linked from the index page of the class.

Specific notes about experiments in R [added 2019-Aug-12]

Some of the students who tried calculation in R successfuly changed "2" of "kscenario <- 2" to "1", "3", or "4". You can also try to change "500" of "depth <- 500" to "4000" or "100" etc., and "3" of "tssrdouble <- 3" to "1.5" or "4.5" etc., and re-run.

Section 2 of the term report assignment

"One paragraph" was not a good way of assignment. (The typical length of a paragraph depends on the cultures of schools.) I should say "approx. 5 lines, or 80 words" for each item.

I wanted you to discuss major causes that can change total energy of the climate system. I regret that I mentioned "global mean temperature" as something that is likely to be proportional to the total energy. Some processes have strong influence to temperature though they do not change total energy significantly. (I included temperature because discussions of feedbacks usually start from temperature.)

• External forcing to the climate system
  • (1) Solar activity
    • (I wanted this.) Energy flow by radiation (electromagnetic waves) of all wavelengths together: energy input to climate system (40-year experience: +/- 0.1% of the total, likely temperature change +/- 0.1 deg. C)
    • Ultraviolet part (larger relative variation than total), absorbed in the stratosphere, causing temperature change in the stratosphere. (Difficult to discuss how it affects temperature in the troposphere and at the surface. Also difficult to discuss how it affects ozone concentration in the atmosphere.)
    • (I did not want this, though electromagnetic waves are involved to some extent.) "Solar flares" ... violent phenomena, of the time scale of one day. Involving magnetic fields, high-energy particles (protons etc.) and some electromagnetic waves. They may cause damages to electric infrastructure and radio wave transmission. They are not considered important for climate change unless they occur frequently.
  • (2) Volcanic activity
    • (I wanted this.) Stratospheric aerosols (mainly droplets of sulfuric acid made from sulfur dioxide gas) in the stratosphere... reflecting solar radiation
    • Mineral particles (volcanic ash) ... important at local scale, but not at global scale
    • Carbon dioxide ... greenhouse effect, important at long time scale (e.g. million years).
  • (3) Concentration of carbon dioxide in the atmosphere
    • Absorption and emission of infra-red (terrestrial, long-wave) radiation ... greenhouse effect
    • Note: both absorption and emission are important.
    • Note: "trapping heat" is not scientifically precise expression, though popular. "trapping sunlight" or "reflecting input energy" sometimes found in popular writing are wrong as scientific explanations.
• Agents internal in the climate system, which cause feedbacks
  • (4) Snow and ice
    • (I wanted this.) Reflecting solar radiation. (Causing positive feedback to temperature.)
    • Melting and freezing causes changes of temperature. It is one of the important processes that cause temperature change. But, it is change of partition of energy within the climate system.
    • Snow cover and sea ice act as insulators of heat exchange between atmosphere and soil, or between atmosphere and sea water, respectively. It affects temperature change. But, it is also change of partition of energy within the climate system.
  • (5) Water vapor
    • (I wanted this.) Absorption and emission of infrared (terrestrial, long-wave) radiation ... greenhouse effect. (Causing positive feedback to temperature.)
    • Condensation and evaporation causes changes of temperature. It is one of the important processes that cause temperature change. But, it is change of partition of energy within the climate system.

Section 3 of the term report assignment

I wanted to exclude (such actions that people categorize as) "mitigation" from the report assignment. But apparently my intention did not reach all of you. There are some answers saying that "our environmental policy should not be just CO₂ emission reduction", which I count as relevant answers.

Countermeasures to (impacts of) climate change

• Adaptation
  • migration (across international boundaries)
    • already considered for small island countries (vulnerable to sea level rise + storm surge)
    • not yet seriously discussed for deltas (in conditions similar as above), dry countries (vulnerable to water balance change), but I think we should consider it there in the near future.
  • land use change ... withdrawal from vulnerable land (need regulation?)
  • construction ... levees, etc. (limited by finite resources)
  • reduction of flood disasters by alarms, evacuation, etc.
  • changing crops, changing crop calendars
  • Can wildlife adapt?
    • Perhaps we cannot preserve ecosystems in place.
    • How can we conserve species?
    • How can we conserve "ecosystem services"?
    • I am not an expert. See, for example, Hannah (2015), Lovejoy & Hannah (2019).
• "Mitigation" (as experts of climate change policy call since around 1995)
  • reduction of emission of CO₂ etc.
    • reduction of energy demands
    • use of energy resources with no (or smaller) emission
      • renewable energy: solar, wind, hydro, biomass
      • nuclear (fission)
        • problems
          • radioactive wastes -- need long-term strict sequestration
          • risk of accidents (spread of radioactive pollution)
    • (special attention to) transportation (automobiles, aeroplanes, ships) which currently depend on petroleum very much.
      • automobiles: internal combustion engines can be replaced by electric motors.
      • aeroplanes: difficult to be replaced. Maybe we must reduce demands.
  • CO₂ removal from conbustion exhaust gas ... usually included in "mitigation", though technically not much different from CO₂ removal from the atmosphere.
    • much larger volume than SOx and NOx (toxic pollutants) removal from exhaust gas. Practically impossible for vehicles to take CO₂ back home.
    • significant energy cost
    • security of eventual storage (see discussion below about CO₂ removal from the atmosphere)
  • enhancement of natural carbon storage (reforestation etc.) ... usually included in "mitigation".
• CO₂ removal from the atmosphere
  • expert consider this necessary to achieve net zero emission.
  • problems
    • high energy cost
      • some inevitable
      • some can be reduced by technology development
    • security of eventual storage (though less strict than nuclear wastes, the mass is huge.)
      • instantaneous breakdown ... dangerous
      • long-term leak
        • environmental problems (esp. to sea bottom biosphere)
        • intended effect is lost. (sequestration should be kept ca. 1000 year)
• Intervention to energy balance of the climate system (enhancing reflection of solar radiation etc.)
  • [Notes added on 2019-Aug-09]
  • (It seems possible to control global and annual mean energy balance, but it will accompany regional and seasonal changes which may be undesirable.)
  • (Injecting aerosols in the stratosphere seems to be the most feasible way. If it is implemented, direct solar radiation at surface will decrease very much, thus concentrated use of solar energy will be ruined. This is an example of conflicts between "geoengineering" and "mitigation".)

Notes on water [added on 2019-Aug-09]

Shortage of water is one kind of important possible impacts of climate change on the human society. But, we should distinguish the two items:

• Safe water for drinking and keeping human bodies clean ... issue of human rights
• Water resources for agriculture (irrigation), industry, or urban facilities ... issue of regional economy, even though some of them are necessary for the contemporary global human society to survive.

The amount of drinking water is much less than the amount of irrigation water. So, scarcity of one may happen in different place and time from scarcity of the other. Even in changing climate, availability of safe drinking water can be kept high, if the goal is given high priority in international policy-making. But, it is very hard to move irrigation water from one region of the world to another. Sustainability of food production with irrigation is much uncertain. As a way to adapt to climate change, maybe we need to have technology to grow crops with less irrigation water.

Other environmental issues (not directly related to CO₂ emission)

• Radioactive pollution (included in the discussion above)
• Plastics
  • harm to aquatic lives
  • wasteful use of non-renewable resources
  • How to reduce use of them, keeping hygiene? We need clean and popular ways of re-use.

Another interesting cause-and-effect chain (rather than "climate change -> impact")

land use change -> change of biogeochemical cycles -> change of greenhouse gases in the atmosphere -> contribution to climate change