"why can't someone just go out and measure?"

Here is another good post at Climate Skeptic.

Excerpts (see the post for links):

One of the oddities about climate science is just how hard it is to get research that actually goes out and gathers new empirical data. Every climate scientist seems firmly rooted in the office tweaking their computer models, perhaps as an over-reaction to meteorology being historically mostly an observational science. Whatever the reason, study after study masticates the same old 30 or 40 historical proxies, or tries to divine new information out of existing surface temperature records. If you ever read Isaac Asimov's book Foundation, you might remember a similar episode where a character is amazed that scientists no longer seek out new empirical data, but just manipulate data from previous studies.

The issue of how much urban heat islands bias surface temperature records is a case in point. The two most prominent studies cited by the IPCC and the RealClimate.org folks to "prove" that urban heat islands don't really exist are Peterson and Parker. Parker in particular really bent over backwards to draw conclusions without actually gathering any new data...
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I have always wondered, why can't someone just go out and measure? It can't be that expensive to send a bunch of grad students out with identical calibrated temperature instruments and simultaneously measure temperatures both inside and outside of a city. At the same time, one could test temperatures on natural terrain vs. temperatures on asphalt. A lot of really good data that would be critical to better correction of surface temperature records could be gathered fairly cheaply.
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Unfortunately, this need for amateurs to actually gather empirical data because the climate scientists are all huddled around the computer screen is not unique in this case. One of the issues with proxy data like tree rings, which are used to infer past temperatures, is that past proxy studies are not getting updated over time. Over the last several decades, proxy measures of temperatures have diverged from actual temperatures, raising the specter that these proxies may not actually do a very good job of reporting temperatures. To confirm this, climate scientists really need to update these proxy studies, but they have so far resisted. In part, they just don't want to expend the effort, and in part I think they are afraid the data they get will cause them to have to reevaluate their past findings.

So, Steve McIntyre, another amateur famous for his statistical criticisms of the Mann Hockey Stick, went and did it himself.