Australasian Science: Australia's authority on science since 1938

Is Gas Really Better Than Coal?

By Simon Grose

Despite the best current knowledge and intentions we could be accelerating climate change.

While conflict between mainstream science and climate change sceptics dominates public discourse, attention is diverted from a more important issue: are measures deemed to slow global warming actually effective?

One key assumption is that replacing coal with gas as a fossil fuel for electricity generation is a good move because burning gas produces approximately half the amount of CO2 per unit of primary energy compared with burning coal.

Researchers from Southern Cross University recently inflicted a small puncture in that assumption by sampling methane levels in southern Queensland coal seam gas fields. They found levels higher than beyond the gas fields (see p.8), indicating that methane – a more potent greenhouse gas than the CO2 that would be emitted if the methane was burnt – was leaking from the valves and pipes.

This provoked media attention, umbrage from the gas industry and calls from the Greens and others for more research. A year earlier, such research was published in Climate Change Letters by Tom Wigley, an Adjunct Professor at the University of Adelaide and senior research associate at the US National Center for Atmospheric Research.

While the SCU research provided indicative data, Wigley’s work aimed to compare the overall warming effects of emissions from coal and gas. Unlike emissions from gas-fired plants, emissions from coal-fired plants contain sulfur dioxide and other particulates that have a cooling effect by blocking solar energy from the lower atmosphere. Wigley modelled the effect of reduced SO2 emissions if coal-fired plants are closed and methane emissions increase from gas systems.

He told his model there would be a 50% decrease in coal use from 2010 to 2050, replaced by gas, and asked it to estimate the effect on global temperatures of subsequent lower SO2 emissions and increased methane emissions ranging from 0% to 10% of gas extraction volumes.

The result is a depressing challenge to the “gas better than coal” assumption. The model found that a shift from coal to gas would slightly accelerate climate change through to 2050, even if no methane leaked from gas operations. If gas kept replacing coal, and methane leaked at a worst-case 10%, this effect would continue through to 2140.

He concluded: “Unless leakage rates for new methane can be kept below 2%, substituting gas for coal is not an effective means for reducing the magnitude of future climate change.”

The gas industry has safety and profit incentives to limit leakage, but it is a daunting challenge to peg losses below 2% as gas passes from wellhead to processing plant and final users via pipes and ships.

Wigley’s results throw doubt not only on the climatic impact of replacing coal with gas but on current carbon accounting methods that rely on averages and occasional sampling. More research is needed, not only into the atmospheric effects of coal and gas emissions, but also into reducing leakage from gas systems.

Simon Grose is a Director of Science Media (