Ok. Let's pretend that's the case, and that the issue of global warming has become so hopelessly politicized that whenever the subject is brought up, all sides' arguments ought to be mistrusted. Is there a way to objectively analyze the data?
To do so in a way that satisfies skeptics' criteria, the party interpreting the data would need to have no personal stake in the matter. (This of course raises the problem that you're relying on the opinions of non-experts, but remember: to skeptics, having studied an issue gives you a vested interest in it, so the more knowledgeable you are, the more biased, and therefore untrustworthy, are your opinions.) To be even more objective, you'd want to make it a blind study: show only the raw data points with no identifying characteristics.
That's exactly what the AP did (story courtesy of Joe Romm): they chose a group of statisticians (no vested interest in climate science) to analyze de-labeled temperature data. In other words, the statisticians had no idea they were looking at temperatures, and were simply trying to spot trends in a set of valueless numbers. It's the ultimate unbiased examination of temperature.
Much to the dismay of skeptics, the statisticians came to the same conclusion as scientists: the numbers represented an undeniable upward trend, no matter whether you start from 1880, 1979, 1998, or 2005. Only then were they told that the numbers represented temperatures, at which point "upward trend" means "warming, not cooling." Here's the AP story: