Plan B … continued

23rd May, 2010 - Posted by admin - Comments Off

Plan B and long-term greenhouse gases

There are examples where Plan A and Plan B are in conflict. Plan B may divert some effort from reducing the emissions of long-lived greenhouse gases. A simple example is given later. It will, of course, be necessary to limit the atmospheric concentrations of long-term greenhouse gases – probably at a greater rate than Plan A envisages – as eventually these alone could force the climate above a danger threshold. Plan B more than counters any increase emissions by extracting carbon dioxide from the atmosphere.

Plan B advocates extracting carbon dioxide from the atmosphere by e.g.

  • Constructing buildings from wood from sustainable sources
  • Burning biomass (for power) with carbon capture and storage
  • Using biochar to capture carbon

Practical differences between Plan A and Plan B

Policy differences between Plan A and Plan B can be seen from considering Unger et. al. “Attribution of climate forcing to economic sectors”. This paper aggregates climate forcing agents and attributes them to broad economic sectors. “Industry” is one of these economic sectors.

Unger et. al. estimate the effect of “Industry” on climate over the period of a century: It is assumed that the emissions continue at a constant rate for the whole century. At the beginning of the century “Industry” has a net cooling effect through the emissions of sulphate and aerosols. But these are short-lived. After about forty years the effects of longer lived species – nitrous oxide and carbon dioxide – accumulate to balance this cooling. After a century has passed the effect of a century of emissions industry is strongly warming.

If “Industry” were stopped at the beginning of the century, there would be an initial warming effect followed by a stronger cooling effect later in the century. Stopping such a major section of economic activity is too unrealistic to even be a thought experiment – but, if it were to happen, the initial warming effect of “stopping Industry” could push the climate past the the dangerous 2 degrees Celsius limit. More practical examples are not hard to find. Consider the use of internal combustion engines. Are they best fueled by petrol (gasoline) or diesel?

The entry in Wikipedia on diesel has

Diesel-powered cars generally have a better fuel economy than equivalent gasoline engines and produce less greenhouse gas emission.

and

Diesel combustion exhaust is a major source of atmospheric soot [black carbon] and fine particles, which is a fraction of air pollution implicated in human heart and lung damage.

Plan A favours the use of diesel over petrol because of it produces less long term climate warming. Plan B favours petrol over diesel because it avoids the short term warming caused by soot in diesel exhaust.

Summary

Plan B will give further options if, in the short term:

  • unexpected positive climate feedbacks occur
  • there is a failure to meet emission reduction targets

Plan A leaves no options available if these contingencies occur.

Plan A is government’s current model for addressing climate change. It plans to

  • reduce emissions of long lived greenhouse gases

Plan B would

  • place an emphasis on short lived greenhouse forcing agents
  • use geoengineering to cool the Earth
  • extract carbon dioxide from the atmosphere

Posted on: May 23, 2010

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