footprints than typical omnivorous diets, while those who ate 'paleolithic' and ketogenic diets had higher dietary-carbon emissions due to their animal sourced foods. A 2020 study found that the climate change mitigation effects of shifting worldwide food production and consumption to plant-based diets, which are mainly composed of foods that require only a small fraction of the land and CO2 emissions required for meat and dairy, could offset CO2 emissions equal to those of past 9 to 16 years of fossil fuel emissions in nations that they grouped into 4 types. The researchers also provided a map of approximate regional opportunities. According to a 2021 Chatham House report, supported by the United Nations Environment Programme, a shift to "predominantly plant-based diets" will be needed to reduce biodiversity loss and human impact on the environment. The report said that livestock has the largest environmental impact, with some 80% of all global farmland used to rear cattle, sheep and other animals used by humans for food. Moving towards plant-based diets would free up the land to allow for the restoration of ecosystems and the flourishing of biodiversity. A 2022 study published in Nature Food found that if high-income nations switched to a plant-based diet, vast swaths of land used for animal agriculture could be allowed to return to their natural state, which in turn has the potential to pull 100 billion tons of out of the atmosphere by the end of the century. Around 35% of all habitable land around the world is used to rear animals used by humans in food production. Politics A reduction in meat consumption and a shift to more plant-based diets is needed to reach climate targets, addressing public health problems, and protecting animal welfare. Research has been done on how to best promote such a change in consumer behaviour. Some public health organisations advocate a plant-based diet due to its low ecological footprint. These include the Swedish Food Agency in its dietary guideline and a group of Lancet researchers who propose a planetary health diet. Vegan climate activist Greta Thunberg also called for more plant-based food production and consumption worldwide. A 2022 report by the Stockholm Environment Institute and the Council On Energy, Environment and Water included protecting animal welfare and adopting plant based diets on a list of recommendations to help mitigate the ecological and social crises bringing the world to a "boiling point". See