Agree to Disagree
Debate in a non-hostile environment
How to look for slowdowns
How much does the warming rate need to slow by, to qualify as a slowdown? Slowdowns don’t usually start abruptly, they slowly develop. They usually finish slowly as well. So how do you determine how long a slowdown is?
All of these are difficult questions, and the answers will vary, depending on who you ask.
I am going to take a pragmatic approach. I am going to use the GISTEMP Global Land and Ocean temperature series, for this exercise. Some people feel that GISTEMP is “adjusted”. If that is true, then it should be hard for me to find a slowdown. If I find one, then we can be confident that there really was a slowdown.
The average warming rate for GISTEMP, over the date range from 1970 to 2018, was +1.8 degrees Celsius per century. I am going to call any date range with a warming rate of +1.0 or less (degrees Celsius per century), a slowdown.
+1.0 degrees Celsius per century, is about 55 percent of +1.8 degrees Celsius per century.
So my criteria for determining a slowdown, is the equivalent of a car with an average speed of 100 km/h, slowing down to 55 km/h, or less.
I think that most people would regard slowing down to 55 km/h or less, from an average speed of 100 km/h, a considerable slowdown.
Graph 1 (see below), is a normal global warming contour map. The colours indicate what the warming rates were, for every possible date range, and for every possible length of date range. There is a legend below the contour maps, which shows the warming rates for each colour.
It is hard to see exactly where the slowdown is, on the normal contour map, because there are many colours being used for the different warming rates that are less than or equal to +1.0 degrees Celsius per century.
To make the slowdown easy to see, we can change the global warming contour map to use only 2 colours:
— yellow for any date range with a warming rate that is less than or equal to +1.0 degrees Celsius per century
— dark-orange for any date range with a warming rate that is greater than +1.0 degrees Celsius per century
Look at Graph 2 (see below). Every date range that is yellow, is a slowdown.
Notice how they occur at relatively regular intervals. But the gap between them is not exactly regular, because the climate is partly chaotic.
Also, notice how the slowdown centred on 2007.5 is the biggest slowdown since 1970. But warmists insist that there was no slowdown.
Graph 2 makes it clear, that it is possible to find date ranges of length 14 years, which have a warming rate of less than or equal to +1.0 degrees Celsius per century.
Conclusion – there was a recent slowdown, which lasted for about 14 years. It started in July 2000, and ended in July 2014.
GISTEMP – Global – Land and Ocean – 1970 to 2018