Medicynical note: It was about a year ago that the CO2 level crossed the 410 ppm level.
The relationship between warming and human activity is apparent and rational people accept it as fact. Even the deniers have evolved and now agree warming is happening. They, however, dispute the cause and deny the possibility of catastrophic effects from human activity despite the clear correlation between such activity, hydrocarbon use as fuel, and atmospheric warming. Yes, in the distant past (a past ironically denied by many religious fundamentalist deniers) CO2 was as high or higher. But that was likely from volcanic activity and prior to man’s existence.
But absolute belief in bible stories doesn’t fully explain the lack of response by the US to this clear and present danger. In the past 30 or so years climate change has become a political litmus test. Decisions are filtered through short term financial special interests; the fear of change, religious shibboleths, and simple denial of reality because of political animosity.
It appears that only a massive tragedy along with similarly massive financial losses has any chance of getting a response. And next year or sooner there will be another chart showing the CO2 crossing the 420 ppm level.