When we burn fossil fuels like coal, and gas to create electricity or power our cars, we release CO2 pollution into the atmosphere. Electricity generation is the main cause of carbon pollution in Australia as 73% of our electricity comes from burning coal and 13% from burning gas.
https://grist.org/article/2010-11-23-greenhouse-gas-pledges-arent-enough-to-stop-global-warming/
Humans clear vast areas of vegetation around the world for farming, urban and infrastructure development or to sell tree products such as timber and palm oil. When vegetation is removed or burnt, the stored carbon is released back into the atmosphere as CO2, contributing to global warming.
Some that farmers use also release nitrous oxide, which is another greenhouse gas. According to research, Australian farming contributes 16% of our total greenhouse gas emissions. Using different and different stock feeds can help to reduce farming's contribution to climate change.