Climate change mitigation

May 7, 2012, 12:44 pm

Mitigation is a technical term meaning to render less damaging by reducing one's impact or countering some of that impact by another compensating action. Climate change mitigation refers to actions taken:

  • to reduce the emissions of greenhouse gases (e.g., such as carbon dioxide, methane, nitrous oxide, etc.);
  • to remove heat trapping gases from the atmosphere after they are emitted; or 
  • to reduce the impact of greenhouse gases in terms of the global warming that alters climate.

Climate change mitigation  stands in contrast to climate change adaptation, which refers to actions taken to reduce the impact of climate change once it occurs.

There are a large number of direct and indirect ways of bringing about climate change mitigation. For example, an indirect effect occurs when having built a home under the direct rays of the afternoon sun, you may site a tree to plant beside the structure to shade the place and reduce the absorption of heat.  Whereas, mitigation by a direct effect would be to change your demand for electricity by installing a new technology such as a solar electric (photovoltaic array) system of panels  to generate electricity from ultraviolet radiation. Those actions that use fuel more efficiently or reduce the amount of electricity needed to heat water or Airair in a building are also forms of mitigation. The reliance on geothermal, solar, or wind energy, for example, is a form of mitigation because these diverse fuel sources for electrical generation reduce the burning of fossil fuels which emit the heat trapping vapors called greenhouse gases by climate scientists.

Some examples of widely available fuels that  also produce heat trapping gases arise from the combustion of Woodwood, charcoal,  dung and fossil fuels. Fossil fuels are a dominant source of  carbon dioxide emissions from the reliable but diverse applications of  oil, natural gas or coal. Fuel switching, or diversification of non-carbon fuel sources that reduce emissions of heat trapping gases are policies that mitigation is designed to facilitate. In order to stabilize the level of carbon dioxide in the atmosphere in the near to long-term future, mitigation is one type of primary options in response to global distress due to air and water contamination.

Mitigation refers to those options that prevent pollution or retard the rate at which climate change is accelerating due to accumulating vapor gases that absorb and emit infrared radiation (heat).  Two varieties of mitigation are 1) reducing the build-up of greenhouse gas emissions into the atmosphere by source restrictions and 2) by increasing the absorbing  capacity of  ground cover (sinks), or using technology to capture heat trapping gases. These varieties are called source-oriented and effect-oriented strategies for mitigation by climate policy specialists. Mitigation is viewed as one of three potentially viable social and economic responses to global warming, along with adaptation and indirect policy options.

There are a large number of climate change mitigation plans. One of the most famous approaches to mitigation is the "wedge" approach but forth by Steven Pacala and Robert Socolow, which proposed a set of fifteen approaches ("wedges") to stabilize emissions of greenhouse gases at the 2004 level of approximately seven billion tons of carbon per year (GtC/year) "for the next 50 years, even though they are currently on course to more than double." They assert:

"Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world’s energy needs over the next 50 years and limit atmospheric CO2 to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no element is a credible candidate for doing the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used."

The fifteen wedges proposed by Pacala and Socolow, each capable of achieving one-seventh of the goal (i.e, one billion tons of carbon per year) by 2054 (fifty-years after Pacala and Socolow's initial paper), are shown in the following table:

 Approach

 Comment

Category I: Efficiency and Conservation

 

 1. Efficient vehicles

Achieve fuel efficiency of 60 mpg (7.8 L/100km) (twice that of 2004) for 2 billion cars (~4 times that of 2004) with fuel type and distance traveled unchanged.

 2. Reduced use of vehicles

 Reduce average distance traveled per vehicle by half (to ~5,000 miles per year) - efficiency and fuel type unchanged for 2 billion cars

 3. Efficient buildings

Apply energy efficient space heating and cooling, water heating, lighting, and refrigeration in residential and commercial buildings to reduce emissions associated with buildings by about one-fourth.

 4. Efficient base-load coal plants

Improve power plant efficiency from an  average of 32% (in 2000) to 60%.

Category II: Decarbonization of Electricity and Fuels

 

 5. Gas base-load power for coal base-load power

 Substituting natural gas for coal for 1,400 GW of power (this is four times as large as the total current gas-based power.

 6. Capture and storage of CO2 at base-load power plant

Installing carbon capture and storage (CCS) technology (which prevents ~ 90% of the fossil carbon from reaching the atmosphere) at 800 GW of baseload coal plants or 1600 GW of base-load natural gas plants. See Carbon capture and storage.

 7. Capture CO2 at H2 plant

The hydrogen resulting from pre-combustion capture of CO2 (part of #6) can be sent off site to displace the consumption of conventional fuels rather than being consumed onsite to produce electricity.

 8. Capture CO2 at coal-to-synfuels plant

 Large-scale production of synthetic fuel (synfuel) from coal accompanied by carbon capture and storage (CCS) at plants producing 30 million barrels of synfuels per day. (200 of the world’s largest synfuels facility in 2004

 9. Nuclear power for coal power

 Displace 700 GW of coal power with nuclear power (~ twice the current nuclear capacity)

 10. Wind power for coal power

Displace 700 GW of coal power with ~2000 GW(peak capacity) of wind power (about 50 times wind power capacity of 2004)

 11. Photovoltaic (PV) power for coal power

Displace 700 GW of coal power with ~2000 GW(peak capacity) of solar power (about 700 times solar power capacity of 2004)

 12. Wind H2 in fuel-cell car for gasoline in hybrid car

 Renewable sources of hydrogen (e.g., from windmills) can displace  conventional fuels. (Though twice the wind capacity of #11 would be required for the same impact)

 13. Biomass fuel for fossil fuel

 Displace conventional fossil-carbon fuels with biofuels such as 34 million barrels per day ethanol (50 times larger than today’s global production rate and with today's approaches would require one-sixth of the world’s cropland.)

Category III: Natural Sinks

 

 14. Reduced deforestation, plus reforestation, afforestation, and new plantations.

 At least one-half billion tons of carbon per year would result if the current
rate of clear-cutting of primary tropical forest were reduced to zero instead of being halved. An equivalent impact would result from "reforesting or afforesting approximately 250 million hectares in the tropics or 400 million hectares in the temperate zone (current areas of tropical and temperate forests are 1,500 and 700 million hectares, respectively)." Another equivalent impact would result from "establishing approximately 300 million hectares of plantations on nonforested land."

 15. Conservation tillage

" When forest or natural grassland is converted to cropland, up to one-half of the soil carbon is lost, primarily because annual tilling increases the rate of decomposition by aerating undecomposed organic matter. . . Practices such as conservation tillage (e.g., seeds are drilled into the soil without plowing), the use of cover crops, and erosion control can reverse the losses. By 1995, conservation tillage practices had been adopted on 110 million hectares of the world’s 1600 million hectares of cropland. If conservation tillage could be extended to all cropland, . . . [a half to one] wedge could be stored in this way."

Pacala and Socolow also note that:

"Stabilization at any level requires that net emissions do not simply remain constant, but eventually drop to zero. For example, in one triangle but looks beyond 2054, 500-ppm stabilization is achieved by 50 years of flat emissions, followed by a linear decline of about two-thirds in the following 50 years, and a very slow decline thereafter that matches simple model that begins with the stabilization the declining ocean sink. To develop the revolutionary technologies required for such large emissions reductions in the second half of the century, enhanced research and development would have to begin immediately."

While Pacala and Socolow's approach has received significant attention, there are other mitigation plans and many efforts to study how to achieve mitigation in specific cases. However, it demonstrates the diversity and scale of approaches required to achieve significant climate change mitgation.

 

Further Reading

Glossary

Citation

Siry, J. (2012). Climate change mitigation. Retrieved from http://www.eoearth.org/view/article/151250

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