Gadget by The Blog Doctor.

Wednesday, January 19, 2011

Global Sea Ice

One of the many indicators that the planet is warming dangerously is the state of the sea ice. Here and here are two of my articles on the Arctic Sea Ice. The argument can be made that just because there are problems with sea ice in one part of the world that doesn't mean that there is a global problem.

Lord Monckton tries to make that point in the graphic below, which is taken from a power point presentation found here.

Monckton claims that "Global sea ice extent shows little trend for 30 years". The graph to notice is the red line at the bottom, the Sea Ice Anomaly. (An anomaly is a variation from average values, which is useful in determining trends in data.) A casual perusal of that line might indicate only a small amount of change. Those who are familiar with Monckton might expect that he has manipulated the graph in some way to make it look as if there has been little change, after all Monckton has form in misrepresenting climate science. In reality the graph is taken directly from The Cryosphere Today site at this link. The problem is with the format of the graph. The Y-axis has a range of 27, while the data has a range of about 3. Formatting the chart this way has the effect of squashing the graph, and so making any trends less obvious. (Incidentally, Cryosphere Today did not attempt to manipulate the presentation of the data, they chose that format so that the anomaly and the area values could be shown on the same graph.)

If we are going to get a clear view of the the changes in the anomaly then we should plot the data with y-axis values that are similar to the range of the data. I have done that in the chart reproduced below.

From Gypsies

Before discussing this graph, I will describe how I produced it. The source for the data, which I saved as global_sea_ice.csv is found here at The Cryosphere Today site. My program, written in R, to plot the data can be found in the appendix.

The red line in the chart is the anomaly data, the black line is the linear trend line. The data is quite noisy (variable) and although the anomaly at the moment is below zero (ie is less than the 30 year average) sometime in the next few years it will climb above zero and then some crazy will claim that Global Sea Ice is not declining. The one thing that is eminently clear is that the trend Global Sea Ice is declining, and the trend is the most important issue, not the current value of the anomaly.

It is amazing that Monckton's nonsense can be so easily taken to pieces, after all he has a huge public profile.

I decided to check the data and perform my own analysis after reading this post at Tamino's Site. I did not do this analysis because I thought Tamino might be wrong, that was not likely, but because Tamino invited his readers to do their own analysis. I was pleased to see that my result was the same as Tamino's.


#################### Global Sea Ice Anomaly #################
##### Written by Stephen Spencer 19/01/2011 ##########

## STEP 1: SETUP - Source File
link <- "C:\\Learn_R\\global_sea_ice.csv"

my_data <- read.table(link,
sep = ",", dec=".", skip = 0,
row.names = NULL, header = T,
colClasses = rep("numeric", 2),
na.strings = c("", "*", "-", -99.99,99.9, 999.9),
col.names = c("Year","Anom","",""))

Title <- " Global Sea Ice Anomaly"

## Ceate Plot
plot(Anom ~ Year, data = my_data, type="l", col = "red", xlab = "Year", ylab = "Anomaly", main = Title)
abline(lm(Anom ~ Year, data = my_data), col = "black")

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