Can a dash for gas be justified?

One of the discomforting ideas I found in Dieter Helm's book, Carbon crunch (see my previous post), was his support for a new generation of gas-fired power stations as a "bridge" to clean electricity generation. My starting position is that I want us to move directly to clean energy as quickly as we possibly can, even if this means substantial economic sacrifices. Do I need to shift my position?

To start to answer that question I have done a quick computer-assisted thought experiment.

Suppose we have a choice of two scenarios. In Scenario 1 we replace a coal-fired power station with a gas-fired station which generates electricity at the same rate. The gas-fired station has an expected life of 40 years and emits 1 unit of carbon a year, compared with 2 units for the coal-fired station. Over its lifetime, the gas-fired station therefore emits 40 units of carbon.

In Scenario 2 we replace the coal-fired station with clean energy - perhaps a combination of wind, solar, wave and tidal power. However, there is a snag. The available technology and infrastructure don't allow us to do this immediately. We have to wait 20 years while a smart-grid is put in place, along with energy storage facilities to cope with times when the sun isn't shining, the wind isn't blowing and the sea is calm. In the meantime, we keep the coal-fired station going and over the 20 years it emits 40 units of carbon.

It's tempting to think that these two scenarios, both of which entail emission of 40 units of carbon, are equivalent in environmental terms. That would be wrong. The rate of global warming mainly depends not on how much carbon is being put into the atmosphere but how much is already there. Let us, for simplicity's sake, ignore the absorption of carbon back into the sea and land through natural processes. The rate of warming in any given year will depend mainly on the cumulative emissions to the year in question. What we are interested in is the cumulative warming effect. In Scenario 2, the emissions are concentrated into the first 20 years. Over 40 years we have the effect of 1200 unit-years of carbon in the atmosphere.

In Scenario 1, by contrast, because our emissions are at a slower rate for the first 20 years, over the 40 years we have the warming effect of only 800 unit-years of carbon. So if we have to wait 20 years for clean energy, it's better to switch to gas for 40 years. In terms of warming effect, breakeven between the two scenarios occurs if we only have to wait 12 years for a feasible clean-energy replacement for our coal-fired station.

So should I change my position and start supporting a dash for gas? Not so fast. I haven't yet looked at Scenario 3, which is to shut down the coal-fired station immediately and do without the electricity it generates until we can replace it with clean energy - perhaps making do with intermittent energy until a full infrastructure is in place. Then there's Scenario 4, in which we replace coal with gas immediately but replace gas with clean energy long before the gas-fired station has reached the end of its useful life, so writing off much of our investment. Scenarios 3 and 4 entail greater economic sacrifice than 1 or 2, but that sacrifice may be justified by the risks from global warming.

I've clearly got more work to do.