A US climate initiative is tackling the largest source of methane gas: cows.
The Obama administration's crackdown on emissions aims to develop an environmentally friendly "cow of the future".
There are 88million cattle in the US, and their cumulative farts, burps and manure produce more gas than landfill sites, natural gas leaks or fracking.
Methane, which has 20 times the global warming effect of carbon dioxide, accounts for 9% of US greenhouse gas emissions. A typical cow emits 250-300 litres of methane a day.
Solutions being explored range from anti-methane pills and dietary supplements to burp scanners and gas backpacks.
The Cow of the Future project in Illinois says the answer is a combination of good diet and good digestion: anti-methane grains processed by the best bovine digestive system from selective breeding.
It is also proposed that energy from methane gas be captured and converted into electricity.
Some experts say significantly reducing the number of cattle - and the amount of meat eaten - would be the most effective solution.
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