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Climate Confusion in Cairns

April 19, 2010

Ken Stewart, April 2010

Cairns, Queensland’s most northerly tropical city, is one of Australia’s premier tourist destinations. Once a quiet port city for the Atherton Tablelands and Cape York Peninsula, it is now the gateway to the Great Barrier Reef, Port Douglas, the Daintree, Kuranda and the Skyrail. Cairns is the 4^th most popular destination for International Tourists after Sydney. Cairns’ population has grown rapidly since the 1980s to 122,731 (2006).

The Bureau of Meteorology (BOM) has two temperature records from Cairns, the Post Office (until 1952) and Cairns Aero, at the Airport. Let’s have a look at Cairns’ climate history.

First, some peculiarities:

GISS (Goddard Institute for Space Studies) regard Cairns Aero as being urban.

BOM regard it as being rural (although in 1996 it was Urban; and Innisfail, a town of some 8,000, is listed by BOM as Urban!)

My analysis runs from 1910 to 2009. I downloaded maximum and minimum annual means from the BOM Climate Data Online site, calculated the average of this, and plotted the results. I also downloaded the GISS pre- and post-homogenisation data and plotted it as well. Finally I downloaded and plotted the Cairns data from the Australian High Quality Climate Site page.

Ready for some fun?

Cairns- PO and Aero

I spliced these for ease of comparison.

Trend of 0.65 degree Celsius per 100 years. In the 1980s it became an International Airport. Bulldog44, in a comment on this site, writes:

“I was transferred to Cairns by Ansett in early 1984 to take over as manager of the Cargo operation. At that time our shed was just next to the tower where the temperatures were taken (and I presume still are).

At that time we handled 4 domestic flights a day, one cargo aircraft and one international flight a week (to a mine in Irianjaya).

After the new air port opened the number of aircraft movements exploded in just a few years to the point where my staff were handling 12 domestic flights a day and 60 international flights a week. And an entirely new International Passenger Terminal had to be added.

The relevance of this being that the engineering base(s) were directly in front of the tower and all the jet engines were tested, blasting their exhaust directly back over the area where the temperature equipment was stationed. That, combined with the extraordinary tarmac extensions adding vast areas of extra concrete to the air port could hardly have failed to affect any readings (in my opinion, of course).”

So it has a recognisable UHI signal!

GISS, in their 2 part homogenisation process, combine all temperatures at a location, then adjust this with the mean of the trend of “nearby” rural stations (up to 250km or 1200km away.)

To their credit, the first part of the process appears to correct for UHI:

A trend of 0.2 C/100 years.

But then, homogenisation increases the warming again to 0.6C.

How does that work? Well, I’m a little tired of trying to work out the GISS shenanigans, so for the sake of argument let’s assume the adjustment is perfectly correct in every way.

Thus, there are now three temperature records for Cairns. But wait, there’s more!

Cairns Aero is part of the Australian High Quality Climate Site network, a set of stations whose data is used to develop the Australian climate record. Only rural stations, not urban, are used in the climate record, theoretically to exclude UHI contamination. Note Cairns Aero is rural!

However, the “High Quality” refers to the fact that the data from all of these sites was adjusted in a homogenisation process by Torok and Nicholls (1996) and another unspecified process in 2004.

This is the result! Cairns Aero, High Quality: