A couple of things
1) Regarding the phrasing: “global warming” has fallen from vogue in this discussion because it implies that the earth heating up is the main or the only issue here. In reality, everything from alterations in ocean circulation, increase in extreme weather events, changes in species distribution, even cooling in some areas, etc are all part of this process – i.e. changes in climate.
2) @Dynamicduo – While it might seem presumptuous to think we’re changing the planet’s climate, that’s exactly what’s going on. Yes, we have only been collecting data since the 1800s, but we have scientific tools to look much farther back. Ice layers at the poles are laid down every year and freeze bubbles into the ice. From cores of the ice, we can read things like CO2 concentrations, even historic temperatures (from water isotopic analyses). Yes, the earth has gone through changes over time – the planet’s orbit changes slightly on a periodic basis, the tilt of its axis also wobbles, etc. All of these things change the climate. What has emphatically never happened before is anything at this scale happening this quickly.
I spend a lot of time thinking about and working on climate science issues and I promise you that the science is pretty bulletproof at this point. Certainly science is never sure, that’s one of its strengths, it’s contingent on future developments and I would be happy to see this disproven, but I think most people who do this for a living would agree that that is VERY unlikely. At this point we need to act, if only in the name of precaution. The consequences would (will?) be dire.