The adjustments thing probably can't go away entirely, it seems like anytime you try to combine many distinct historical datasets you need normalizing adjustments.

For example, the man who empirically determined the normal human body temperature was, as best we can tell, using a thermometer that read too warm. (http://www.realclearscience.com/blog/2015/08/the_average_bod...)

Even with the same nominal weather station recording over the years:

Stations have moved to different locations over the past 150 years, most more than once. They have changed instruments from mercury thermometers to electronic sensors, and have changed the time they take temperature measurements from afternoon to morning. Cities have grown up around stations, and some weather stations are not ideally located. All of these issues introduce inconsistencies into the temperature record.

-- https://www.theguardian.com/environment/climate-consensus-97...

So, in summary, it's virtually impossible to combine a bazillion datapoints recorded over hundreds of years and not need adjustments.