Because this is an official letter from California bishops, is it a moral imperative for Catholics in the State?
Hilarious bishops. They should do standup but that would require backbone.
Nah. However, my conscience as a practicing Catholic for a long time has compelled me to decline to donate to the diocesan appeal, and all other requests by the bishop for money. They do some good work, but money is fungible, and any support I give them inevitably supports crap like this.
These bishops need to butt out of sheer worldly politics. Talk about "clericalism"? It's clericalism on stilts. They do nothing but attract the amused contempt of non-believers and the angry resentment of believers.
All while ignoring the One Thing Needful.
Only to the extent it represents actual Scripture, Catholic tradition, and magisterial teaching, which is very little. The actual document is online here. Most of it consists in a historical review of California's ecology and vague generalizations about being prudent in managing the environment by improving preparation for droughts, etc. Now being prudent is certainly a traditional teaching, but how you actually exercise being prudent is a matter of prudential judgment, and the document's handful of concrete proposals--such as its proposal to lower carbon emissions ("Enact policies that further improve air quality and drastically reduce carbon dioxide emissions and other polluting gases. This includes the substituting of fossil fuels with renewable energy sources as well as developing greater energy storage and efficiency. Ensure that any transition from a fossil-based economy to one of renewable energy does not add to the burden of the poor.")--are matters of prudential judgment not binding on Catholics. Likewise, its scientific opinions, such as the statement, "A broad consensus among scientists worldwide identifies the primary cause of climate disruption as the burning of fossil fuels for energy generation, industry, and transportation," are just that, opinions, not doctrines.