Thursday, February 7, 2013
The Math behind Climate Change: Part 8
Trendlines based on Oceanic Niño Intervals (ONI)
We start again with the data for average Winter temperatures in Greenland from 1955 to 2010. The start and end years were not chosen at random. They coincide with strong La Niña years as measured by climate scientists on a system called Oceanic Niño Intervals or ONI for short. The list of strong La Niña years in this range are as follows.
1955, 1973, 1975, 1988, 1999, 2010
The two years in the 1970s are too close together to make a meaningful trend and they have no El Niño between them, since 1974 was a weaker La Niña. I'll remove 1973 from the list and we get 1955, 1975, 1988, 1999 and 2010.
We use the years to create intervals. In each interval, we mark the highest temperature in red, the average in black and the lowest in blue. These trends are easy to read and take no difficult to explain math. (Note: I am not against difficult to explain math. The math of best fitting curves comes from Gauss and is completely legitimate. My complaint against it is how many different curves can be chosen and the possibilities of cherry picking to make a point.
The three trends tell slightly different stories. All agree that the 1988 to 1999 interval saw much cooler winters than any other span and that the recent span from 1999 to 2010 is by far the warmest interval. While the average in the final interval is only slightly higher than the second warmest interval from 1975 to 1988, the high and the low both increase significantly over the second warmest in each of those categories.
Here are the statements I read most often in the papers of climate skeptics and denialists.
1. The climate is not warming.
2. The warming trend is decreasing.
For all the data I will produce, I will end with a statement addressing these questions for all four seasons in a form
Winter: getting warmer, trend increasing
Tomorrow, we will see the data for all the seasons from Greenland.