The overwhelming consensus of climatologists publishing in peer-reviewed journals is that global warming is real, and caused largely by human activity. But a great many non-peer-reviewed papers exist - junk science, in other words. Grist for political advocates of doing nothing. Don't cite pseudo-science in rebuttal, you'll be wasting your breath. Stick to the peer-reviewed stuff.
Information about atmospheric carbon dioxide over the last 420,000 years is here: