Among the options listed, "eat less red meat so fewer cattle need to be raised" would likely have the most significant impact on reducing global warming.
Cattle farming is a major source of methane, a potent greenhouse gas, and reducing meat consumption can help decrease demand for beef production. This, in turn, can lead to fewer cattle being raised, which could help lower overall greenhouse gas emissions associated with livestock farming.
While other actions like using bicycles instead of cars and promoting sustainable land use practices also contribute positively, reducing red meat consumption directly addresses greenhouse gas emissions from one of the most resource-intensive sectors of agriculture.