Why is global warming so politicized?
Vested financial interests and very strong adherence to in-group beliefs.
For over the past 35 years or so climate scientist have been quite convinced that humans are changing the climate by burning fossil fuels. Left leaning democrats tend to believe scientist on most issues, while right leaning Republians tend to be skeptics and this has become a tribal belief that few are willing to go against. Right leaning people also tend to have financial interests in fossil fuel investments that they would not like to see restricted or phased out. So, they tend to be skeptics like of the science.