Greenhouse-gas emissions from energy use in the water sector

The availability of fresh water and the energy use associated with it, particularly in agriculture, is not thought about much in Britain and Ireland. Nevertheless it is a major issue – as a recent paper by two academics at the University of East Anglia demonstrates.

This paper, “Greenhouse-gas emissions from energy use in the water sector” by Sabrina Rothausen & Declan Conway, draws together the results of 100 scientific studies to sum up the relationship between water use, energy consumption and climate change. The argument of the authors is that the increasing use of water has been underestimated as source of global energy consumption and therefore of greenhouse gas emissions.

For example the use of water in the USA causes about 5% of national greenhouse gas emissions. In India, just 6% of national emissions are caused by power to pumps for field irrigation.

Energy is used in 4 different water sector processes: abstraction and conveyance; treatment and distribution; end use in households, industry and commerce and waste water treatment.

Globally the biggest proportion of 3,800 thousand million cubic meters of fresh water and its associated energy use is taken by the agricultural sector. In international comparisons India’s farmers use 646 thousand million cubic meters, China’s farmers 550 thousand million and the agriculture of the USA 477 thousand million cubic meters.

With a projected growth of world population up to 2030 the demand for food will increase by about 50% and with it an increase in the demand for water and energy. According to an estimate of the UN’s agricultural organisation the global artificially irrigated acreage is increasing at 0.6% each year.

The authors argue for intelligently controlled irrigation systems and energy saving ways for exploiting water resources in order to slow the increase in greenhouse emissions. Globally uniform methods of measurement of energy use in the water sector will also help to control and understand these issues.

It should be noted that this is an article about energy use and climate change. But what will be the impact on agricultural irrigation of post peak oil depletion – e.g. those activated by diesel pumps which will become much more expensive to operate.

The limits to growth are shown particularly strikingly in the water energy interaction. Recent techniques like extraction from tar sands in Canada or shale gas fracking in the USA and elsewhere require massive quantities of water and leave that water heavily contaminated. Deep sea drilling also has huge risks for marine water systems (as we know from the recent accident in the Gulf of Mexico). Biofuels are also perhaps the most water intensive forms of acquiring energy – or, to put it another way, have a very low energy return to (fresh water) invested.

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