This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
The white elephant in the room is http://www.truetex.com/psychrometric_chart.htm
The BEST data (Berkeley Earth Surface Temperature) does not have wet bulb temperatures to help with the analysis. There is a problem analyzing wet bulb temps in the grand scale of dry bulb temps. The relevance of a wet bulb temp is tied to the dry bulb. Averaging Wet Bulb Temps over a month and using that with the average of the dry bulb temp does not yield the average humidity. Maybe someone here knows better and can proclaim "Yes you can do that". I am terribly challenged here because I won't believe them.
An engineer uses the above chart a variety of different ways depending on what activity he is engaged in. Not least of these is "Why is water condensing on the outside of my Y", where Y is a glass, condenser, pipes, storage tank, ... The orchardist asks "Are my apple's going to freeze tonight?" In my youth, dew point was regularly reported on every broadcast, because that dew point was strongly tied to whether or not the smudge pots had to be lit. We had wonderful fog in that part of the world, partly due to the smudge pots.
The chart is not linear.
The exclusion of this chart from the analysis of Global Average Temperature boggles my mind. Attempting to make an average temperature isn't wrong. It isn't right either. Temperature is a proxy for energy. The Psychrometric chart lets us convert the temperature information into energy. The error bars implicit in not using Energy are huge.
55F 10%Hum => 14 BTU/lb
55F 50%Hum => 18 BTU/lb
55F 80% hum => 23 BTU/lb.
We can't even guess what the humidity was tied to each temperature.
The average error police will count the number of measurements and the error reading the temperature and give you an error bar associated with averaging. They do not give you a number associated with the implicit error added by ignoring the enthalpy problem.
All of this is an attempt to illuminate why it is my Gut says "Those boys calculating global average temperatures and modeling the planet need JEB on their team with is Rod of Terror, to scare them back to the science!"
Sometimes the rod of terror takes the form of a 2X4. Sometimes it is a train trundling down the tracks. Mass matters folks. You may have the right of way in your 10 ft punt. That 200,000 ton cargo vessel traveling to the Port WILL NOT STOP in its tracks if you sail in front of her. If people start whining that they couldn't see the 200,000 ton vessel in the water, my answer is "GET THE F out of the water, you have no business being there if you can't see the shipping lane on your chart".
The Met Office Hadley Centre produces a humidity-related temperature dataset called HadISDH, and some information about it is given on this webpage:
The webpage gives a link to a paper at the top, and provides separate graphic image links for the figures in the paper. They give a global average wet bulb temperature anomaly (Tw) versus time in Figure 12b. The Tw curve looks fairly similar to the more usual dry bulb temperature anomaly curve in Fig 12a, but the Tw curve peaked in 1998. There is also a relative humidity curve in Fig 12f and it looks like global relative humidity has been steadily decreasing in the 21st century.
It is a bit surprising that you don't hear more about the wet bulb temperature idea from the climate science community, as they tend to be obsessed with heat waves and the possibility of people dying in them and areas becoming too hot to be habitable. The Tw parameter is a bit more informative when it comes to assessing the effect of heat waves.
Decreasing atmospheric moisture content is more indicative of moisture shifting to the poles as ice.
The lower moisture content certainly means that temperatures will be more extreme as the specific heat of dry air is is substantially lower than that of moist air. The same amount of heating from the surface will make the air warmer and, if the air is in contact with colder air or surfaces, it will cool more quickly and further, never having gained the heat that it would have were it moist.
Of course, being drier also means that the reduced water vapour has a lower potential for the air to cool if it doesn't get in contact with colder air or surfaces. But it does cool more rapidly over water surfaces as the drier air more readily accepts water vapour; so the evaporation cools the air further, somewhat reducing the air's capacity to carry water vapour. There are positive and negative feedbacks in even that part of the climate system.
The first few links on that page actually use C instead of Anomalous C.
One of the charts shows most of the worlds dew points seemingly climbing which would say that the humidity is increasing not decreasing wouldn't it?
I am still suggesting plotting all the data. Creating a world humidity anomaly is harder than the temperature anomaly. I keep trying to express my concern with averages. I keep failing to express it in a way that Warmists understand. Averages are an awesome tool. Be very wary of averages because they will bite you.
How in the world did David Robinson (Basket Ball Center at > 7' tall) get into the Nuclear Navy? Apparently he was a good student, but practically, I could barely get around the engine room at 6' 3".