London: China`s groundwater irrigation system is responsible for spewing more than 30 million tonnes of carbon dixoide (CO2) per year into the atmosphere, says a research.
Groundwater used for crop irrigation in China has grown from 10 billion cubic metres in 1950 to more than 100 billion today, according to a study by the University of East Anglia (UEA).
Pollution is caused by the huge amount of energy needed to pump water from underground - in some areas from an average depth of 70 metres.
This research is the first to estimate that the pumping systems which support this immense irrigation network annually produce 33.1 MtCO2e (33.1 mega tonnes of CO2 equivalent), the journal Environmental Research Letters reported.
China is the world`s largest greenhouse gas emitter, with around 17 percent of it coming from agriculture. Irrigated agriculture in China produces 70 percent of the country`s grain. But it takes some 500 litres of water to grow the wheat for one small loaf of bread, according to an university statement.
The research team used extensive survey data collected from 366 villages in 11 provinces. They up-scaled these results to calculate the emissions created by groundwater pumping across China`s remaining 20 provinces.
Declan Conway, from UEA`s School of International Development and the Tyndall Centre, said: "Generally, there is a surprising gap in research knowledge about the energy required for water use. It is vital that we understand the sources of greenhouse gas emissions in agricultural water use to design and implement sustainable policies for the future."