Digesters on dairy farms produce biogas from cow manure Rudmer Zwerver/Shutterstock When fuel ran out during the second world war, some farmers in Germany and France made their own fuel by covering cisterns of manure and capturing the methane that was generated. Now, governments are pushing an upgraded version of that technology, called an anaerobic digester, as a way to reduce dairy farms’ greenhouse gas emissions. But some researchers say spending on digesters could have unintended consequences for the climate and human health. “Is this money more effective in climate reduction than other strategies like building solar panels?” says Rebecca Larson at the University of Wisconsin-Madison. “That’s something that should be examined… but in terms of livestock it’s one of the highest performing mitigation measures that we have.” Agriculture accounts for about one-third of human-caused emissions . In the US, about a third of this is from cows belching, but another 14 per cent is from manure.…