> In principle if one used already the Hawaii data for the CO2 measurements, it seems it would make sense to use temperature measurements from the same location.

I'm not an expert on this, but I thought CO2 is well mixed within the atmosphere, and I think surface temperature (or tropospheric temperature at whatever height) is certainly not "well-mixed" across the globe. So I'm not sure if this is really a good thing to do. I think one should compare the well mixed CO2 rises with some kind of average earth temperature.