Really? Apparently people born after 1985 have never experienced a colder than average month anywhere on the planet. I wonder if these people can remember what happened last year? I wonder if they have ever actually done an average calculation in their life. Being forced to calculate Variance and std dev might seem too much of a burden these days with R, mathCad, Mathematica, ti-XXX, all available to do it for us, but actually handling the data sorts of beats it into your brain and forces people like Pascal to ask silly questions about distributions. How many different definition of average are there? Mode, Median, Mean being obvious starting points, but there are more out there: time weighted means, in tolerance means, out of tolerance means, ...
I plotted all the data that HadCrut released. GISS temp anomaly looked to be right in line with all of the data. When you plotted all of the data though, you could barely see in the increase in that anomaly. You could see lot so of temperatures though. Such a ride range of temperatures we experience around the planet EVERY DAY!
Dr. Muller and others insist that they can reduce all those down to a single data point and never worry about the implications of Enthalpy. I wish I could have told that to my Thermo, Fluids, Heat Transfer and Materials professors. I am happy that the nuclear reactor I ran ignored these modern science whizzes. Cold water is a little denser than hot water. Put two columns of equal diameter and the cold column will push the hot column up. Our subs are really quiet because of this. Enthalpy IS involved. You can get close without it, but the difference isn't insignificant. When you are talking about the mass of the air on this planet, the differences are even less insignificant.
My understanding of this story is that it is the monthly global average temperature (based on the specific temperature dataset used by NOAA) that has exceeded the 20th century average global temperature for the same month for a long time, currently 332 months or about 27 years. [For the first 15 of the 27 years, the 20th century average global temperature for the month would not be known at the time as the century had not finished].
The Grist writer has hyped the story to make it look as though people up to the age of 27 have only ever experienced above average monthly temperatures wherever they live.
I think the WUWT position on this issue is that it arises from continual upwards temperature adjustments that get made to the temperature dataset, discussed in this link from 3 months ago when the running total was at 329 consecutive months: