Why nights can warm faster than days - Christy & McNider vs Davy 2016

At WUWT, Anthony Watts has written about a new paper by John Christy and Richard McNider, which was published in Journal of Applied Meteorology and Climatology of the American Meteorological Society. The researchers were looking at trends in summer-time maximum temperatures centering the analysis on three cities in Alabama, and using stations in Alabama and Tennessee. The purpose was to come up with a methodology to construct "long-term datasets by accounting for heterogeneities or changes in the observed time series without the use of station metadata".

There was a press release for the paper, which seems to have been picked up by almost no-one, except WUWT (archived here). In it the authors say:

In addition to creating some arcane mathematical tools useful for creating climate datasets, the team also found daytime high temperature data is less likely to be contaminated by surface issues — such as deforestation, construction, paving and irrigation — than nighttime low temperatures.

However I cannot find anything in the paper that supports that specific finding of contamination, or not strongly so.

More about the hot weather in North America, and more

In the comments today, under the article about the extreme weather around the world these past few days, there was a claim that "It was warmer in the US in 1955". There was nothing else except a link to two maps of the USA. The top map was labeled 2015 and the bottom map was labeled 1955. The maps were coloured but there was:

• no legend
• no date
• no information that would explain anything about what the charts were meant to represent.

That sort of behaviour is more common on denier blogs than it is here at HotWhopper. Anyway, it prompted me to do some reading and research, and in the process I got diverted a bit into US temperature records, and trends in diurnal temperature range. So this article is a bit of a wander, and a bit long.

How hot was it in 1955 in the USA?

First, though, let's see about the very short and somewhat cryptic comment from HotWhopper reader, Andy Wilkins. He wrote that it was warmer in the US in 1955. But was it? No, it wasn't. At least not if you are looking at mean annual surface temperatures.

Below is a chart showing the annual mean surface temperature for the contiguous USA from 1895 to 2015 (average to November). I've marked the mean temperatures for 1955 and 2015, and this year so far is 1.31 °C hotter than the annual mean temperature in 1955.

Data source: NOAA ClimDiv

Now if Andy had somehow mistaken 1955 for 1954, then the difference between then and now would have still been 0.41 °C . That is it's been 0.41 °C hotter this year so far than it was back in 1954. (Note: The US temps and chart were corrected shortly after posting.)