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U4735x Environmental Science for Decision Makers

Lectures 7 and 8:
Does warming have positive or negative consequences? Are there ways to mitigate the build up of greenhouse gasses?

James D. Hays

I. The Problem

1. Global warming from anthropogenic additions of greenhouse gasses to the Earth's atmosphere has either begun or soon will.

   1. As a consequence we will have to adapt to changing climatic conditions for the foreseeable future.

   2. To eventually end the warming and other environmental damage that may stem from atmospheric carbon dioxide buildup we must stem the atmospheric CO2 increases.

   3. A quick replacement of fossil carbon by alternative energy sources is not possible so reductions in greenhouse gas emissions must come from increasing the efficiency of their utilization and sequestering the carbon dioxide we do emit.

   4. The possible harmful consequences of global warming and other environmental problems that may accompany the atmospheric increase in carbon dioxide content require that we face the problem squarely today and begin the job of correcting it.

2. On balance the environmental changes caused by global warming will be socially upsetting; it will be harder for poor countries to adapt than rich countries.

   1. Possible adverse consequences of global warming.

      1. Coral bleaching (Fig 1).

      2. Reduction in the volume of polar ice and resulting sea level rise.

      3. High latitude regions are especially sensitive to global warming and warming in the Arctic is greater than in lower latitudes (Fig 2).

      4. Changes in high latitude sea ice and snow cover can have a marked effect on polar summer temperatures (Fig 3).

      5. Reduction in tropical agriculture because of higher temperatures.

      6. Increased storminess.

      7. Increased aridity in temperate latitudes.

   2. Any number of other changes that will require adaptation by the human population.

   3. A host of changes that will cause changes in the global ecosystem.

II. What must be done?

1. Stop incremental increases of atmospheric Carbon dioxide to bring atmospheric carbon dioxide emissions into balance with their storage in reservoirs.

   1. This will take time for we will probably not be able to stop the eventual doubling of atmospheric Carbon dioxide from its pre-industrial levels (280ppm) by the middle of this century.

      1. To hold atmospheric levels at 560 ppm will require that the world stay below its 1990 emission rates.

      2. If the U. S. were to reduce emissions by 2010 to 7% below the 1990 emissions rate compared with business as usual would require a carbon dioxide emissions reduction of 35-40%.

      3. Clearly reducing emissions to zero out atmospheric carbon increases will be difficult. Never the less in the 1970's we did reduce the output (Fig 4).

   2. Emissions will not be limited by shortages of fossil carbon (Fig 5, Fig 6).

      1. Coal reserves are about 10,000GT while annual usage of all fossil hydrocarbons is about 6 GT's /yr. Proven reserves are somewhat less but even these should last the world for 100s of years.

2. Increase efficiency of fossil carbon use.

   1. Transportation industry.

      1. World wide transportation produces 20% of global carbon emissions. This has grown from 19% in 1971 to 22% in 1995.

      2. The annual growth rate is about 2.0%/yr (Fig 7).

      3. Efficiencies can arise from the introduction of fuel cell powered cars, combination engines, lighter and smaller cars and improvement in truck and aircraft engine design.

      4. Increased efficiencies of engines will reduce emissions per vehicle but increase in vehicles will make large reductions from current levels difficult by the middle of the century?

   2. Manufacturing.

      1. In 1995 CO2 emissions from manufacturing totaled 2340 MtC and from other greenhouse gasses 166MtCequiv.

      2. Growth rate is about 1.5%/yr.

      3. Cost positive reductions by 2010 could total 300 to 500 MtC and by 2020 700 to 900 MtC

      4. Even with these reductions there will be a net increase in emissions by 2020.

   3. Building sector.

      1. 1995 world emission from buildings was 1732 MtC.

      2. Annual growth rate of about 1.8%.

      3. Kinds of changes that can be made.

         1. Paint roofs white.

         2. Shade trees near buildings.

         3. Better insulation.

         4. Compact florescent lighting etc.

         5. Better air-conditioning.

         6. Barriers.

   4. Agriculture.

      1. 217 MtC emissions in 1995.

      2. 3.1% annual increase.

   5. World total emissions of Carbon dioxide 5504 MtC/yr with a growth rate of 1.8%/yr.

3. Sequester Carbon dioxide emissions in one or more of its natural reservoirs.

   1. The biosphere.

      1. Reforestation.

   2. The ocean.

      1. Dissolve Carbon dioxide in sea water.

   3. The solid earth.

      1. Pump Carbon dioxide into oil wells for secondary recovery.

      2. Pump CO2 into coal mines to recover methane.

      3. Combine CO2 with calcium or Magnesium to make calcium carbonate or Magnesium carbonate.

      4. Problems of stability.

      5. Problems of cost.

Lecture text by James D. Hays, 2002.