What is the exact situation with climate change in terms of C02, temperature and already noticeable impact?

Note on dates: I started looking at this properly over a year ago post the discussion with Liam and Brennan in Berlin.

Existing repo: repo:climate-change. See README there.

Question: why do this? Because I want to inform myself. Not sure that is a good enough reason to pursue it. There's a lot out there.