Friday, August 17, 2007

Beautiful Cape Otway

Ahh, Cape Otway. Such a beautiful place, and the cape otway lighthouse, the most significant lighthouse in Australia, is home to our next piece of analysis:

Maximum temperatures have shown a significant increase in temperature since records first begun here in 1910, despite no real increase since the 60s. Minimum temperatures do not show a significant increase, although they do when analysing from world war 2 onwards. The last decade have been seen constantly warmer minimums.

Unfortunately our time based data is not fantastic, with Midnight, 3am, 6am, Noon, 6pm and 9pm all having limited data. But 9am times actually show a significant decrease. On observation of the graph this is largely due to very hot temperatures (and somewhat dubious) pre 1920. Since then no real pattern has emerged. Given the large increase in maximum temperatures, we would expect 3pm temperatures to also increase, but this was not so.

So is there much we can talk about this wonderful place? Well yes, despite a small sample size, when looking at minimum temperature anomalies vs 3am and 6am, we see that minimum anomalies are up to half a degree warmer, which once again indicates that the minimum temperature is warming up at a greater rate than overnight temperatures. Once again indicating that the minimum is a poor measure of overnight climate.


Philip said...

Jonathan you may well be interested in some comments about cloudiness on either side of the vermin fence in WA, including one by me comparing Merredin and Southern Cross.

Comment #148

philip said...

Jonathan, here is what I think you are seeing in your analysis. Bushland has a much higher albedo than agricultural land, so reflects far less sunlight and we have the clouds over bushland phenomena, which seems to be common here in the West. I see it on a regular basis.

Over time, most locations around Australia will have seen a reduction in bushland in their area (at least as a statistical average).

Reduced bushland = reduced clouds and that quite simply is what you are seeing with increased daytime warming and increased nighttime cooling.

Albedo and water vapour feedbacks swamp any climate effect from CO2.

The way to test this is to pick a site (if one exists) in the middle of a natural park that hasn't seen bushland reduction.

I realize there is a albedo - temperature - heat gain issue here, but that takes us down the thermodynamics road which SM rightly identifies as a morass best avoided.

Jonathan Lowe said...

you might well be right Phillip, unfortunately these type of stations just do not exist. All the stations are basically at post office's, airports or the like. I am trying to get a hold of cloud cover data which could back your theory, however I do believe all such data is only taken in more recent times.

philip said...

Jonathan, I posted some observations about Time of Observation adjustments over at Climate Audit.

In summary. I can't see how a significant time of observation bias can occur in a long series of observations.

The official (NASA?) temperature data has a significant TOB adjusment, which has shown a steadily increasing trend since 1950 and is a large component of the apparent warming over that period.

I assume this is because the yearly data is compiled from monthly TOB adjusted data, which uses a monthly TOB estimating method.

There are legitimate reasons to adjust monthly data for TOB, but not longer time series of a year or multiple years. So any TOB adjustment in the annual data has to be noise from the estimating process.

I need a statistician to confirm that what I think is correct, i.e. you can't have a significant TOB in a long series of observations (or tell me why I am wrong).

If you want a more detailed explanation, post a comment or email me pxbradley-at-gmail-dot-com