www.constructireland.ie - Shifting ground

Shifting ground

Tuesday, 17 March 2009

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Unless greenhouse gas emissions from land are tackled, any efforts to reduce emissions from buildings may fall short in attempting to stave off the worst consequences of climate change. Richard Douthwaite explains how, with a little ingenuity, techniques can be applied to dramatically reduce land emissions whilst simultaneously providing new raw material streams and energy sources

Most people have the impression that the world's climate problem is all to do with the emissions from fossil fuels. That's wrong. About 30 per cent of the problem emissions are due to the way that people are using, or misusing, the land. Consider the most important greenhouse gas, carbon dioxide, alone. About 7.4 gigatonnes of CO2 are released into the atmosphere each year just as a result of deforestation, mainly in the tropics. This compares with about 25.9 gigatonnes of CO2 released by cement production and the burning of fossil fuels combined.

Methane, an even more powerful greenhouse gas than CO2, is produced both naturally and by farming. Bogs and other wetlands are the main natural source - think of will-of-the-wisp, the mysterious lights caused by the spontaneous burning of methane from rotting vegetation seen on bogs at night. Human land-related methane sources, which have grown to be roughly twice as big as the natural ones, include vegetable-matter dumped in landfills, ruminant animals such as cattle and sheep, (these belch methane produced by the bacteria in their stomachs), the growing of rice in flooded fields and the burning of biomass.

Nitrous oxide is another important greenhouse gas. Its agricultural sources include the transformation of nitrogenous fertiliser into N2O and its subsequent release from the soils, biomass burning and, again, the raising of cattle.

Taken together, these land-use-related emissions are so large that the world's climate cannot be stabilised just by phasing out fossil fuels. The way land is used has to be changed drastically as well. Indeed, phasing out fossil fuels could exacerbate land-use emissions by causing land to be switched from one use to another. For example, the production of palm oil on bogs in Indonesia causes the release of more CO2 into the atmosphere when the jungle is cleared so that the plantations can be established than will be saved by the use of the oil in diesel engines for at least 100 years. In the same way, turning Irish grassland into arable to grow, say, rapeseed oil would cause some of the soil carbon to become CO2 in the air and nitrous oxide would be given off when fertiliser was applied.

Because Ireland's agricultural sector is big in relation to the rest of its economy, its land-use emissions are large in relation to its fossil fuel ones too. The ratio is the highest in the EU, in fact. As a result, if we don't change our land use methods quickly, we are likely to have to pay larger fines or make even more drastic cuts in our fossil fuel emissions than any of our EU partners. Since about 27 per cent of Irish emissions come from the land and the overall emissions cuts we are required to make by 2020 could be as high as 30 per cent, we might find ourselves having to make 40 per cent cuts in fossil fuel use if farming emissions can't be brought down.

This has been keeping Department of the Environment officials awake at nights. About half the country's agricultural emissions come from cattle and sheep and they think that Ireland is going to have to make a choice between running cars and keeping cows. However, this choice makes no sense at all. One reason is that, unless the world ate less meat, if Ireland reduced its national cattle herd, global emissions from cattle would not fall. The animals would just be raised somewhere else, perhaps in Brazil, where if forest land was cleared for pasture for them, the world's emissions would actually increase.

A second reason is that the two emissions are not comparable and the choice the country may be asked to make is invalid. The methane from cattle breaks down quite quickly in the air. Its half-life is seven years, which means that half of any quantity released has been broken down into CO2 and water after that period. As a result, half the CO2 which the plants the animals consumed had absorbed as they grew is back in the air after seven years. All feeding grass to cattle has done is to add a methane stage to the natural carbon cycle.