It would be interesting to know whether there has been a significant change in the equipment used to make temperature measurements in Eugene/Springfield over the years and whether the location of the measurements has changed, i.e in ages past was there vegetation in the form of grass or trees near the measuring station and now there is concrete which gets massively hot in the sun?  I suspect that the better measure of climate change may be the nightly lows since they may more accurately reflect true air temperature as opposed to the solar exposure details.