Thursday, December 20, 2007

Sunshine duration accounts for 93% of all warming since 1951

Please Note: Added Edit:

On closer examination of the below analysis, a calculation error was found in the analysis of temperature and sunshine duration. The calculation error has a large effect on the results and the conclusion. The information below should not be taken as evidence or for any talking or arguementive point. On ocrrection of the error it was found that the effect of sunshine duration on maximum tempertaures is a lot smaller than as shown below. This will be discussed in analysis shortly to come. Apologies for the error involved and I will be providing more analysis and more in depth analysis of Australian temperatures in the very near future.
Jonathan Lowe

Abstract: Using twenty two weather stations across Australia, the variable sunshine duration is shown to have significantly increased since 1951. Its correlation with maximum temperature anomalies is highly statistically significant. By eliminating the influence of sunshine duration from the maximum temperature dataset, maximum temperature trends were shown to drop from an average of 1.4 to 0.1 degrees increase per 100 years. Hence the variable sunshine duration accounts for 93% of all positive trends in maximum temperature since 1951 in Australia. Implications of these findings and the relationship of the variable sunshine duration with respect to cloud cover trends and how they is measured will be discussed.

Our introduction on Tuesday laid out that we intend on looking at the variable sunshine duration to see if it has any effect on temperature change over the years.

Using our dataset we found a highly significant increase in maximum temperatures (t = 5.95, p < 0.001). Maybe because we have used urban stations or maybe because the bulk of the weather stations occur on the east coast of Australia (an area which has seen the majority of increase), that the rate of increase of temperature as shown on that graph (linked) is at 1.42 degrees per 100 years, which is more than greater Australia and the rest of the world.

Either way, this doesn't matter, as we are merely looking at the relationship between sunshine duration and temperature. Because some stations have data for maximum temperature that goes back further than sunshine duration (and vice versa), all years that did not have recordings for sunshine duration as well maximum temperatures were eliminated from the dataset for each individual station.

Interestingly, sunshine duration also significantly increased since 1951 (t = 2.58, p = 0.013). The strength of the trend is not as strong as temperature, but is still statistically significant.

The two variables shown on the same graph is shown above. Note that in general when temperatures are high, so too is sunshine duration and vice versa. The last six years of data highlights this. anomalies

The relationship between the maximum temperature per year per station as well as sunshine duration per year per station is shown below. The correlation between them is highly significant (t = 14.71, p < 0.001), and the r squared indicates that 17.5% of the variance of temperature can be explained by sunshine duration.

That might not sound like much, but when we account for the variable sunshine duration (i.e. minus its relationship with temperature off the original dataset), then we can analyse temperature without any influence of sunshine duration. In other words, we can look at temperature trends over the past 50 years by assuming that there has been no trends and no anomalies in sunshine duration at all.

The results are amazing. The following graph shows the temperature trend since 1951 should there be no variance in sunshine duration. The increase in temperature since 1951 still occurs, as is statistically significant (t = 5.8, p < 0.001), but take a look the rate of change of temperature, in particular the formula for the line of best fit as well as the left hand axis.

When taking into account sunshine duration, temperature rise in Australia is at the rate of 0.00099 per year or 0.099 degrees per 100 years. Now a 0.1 degree increase every 100 years is hardly anything to get worries about. It's not going to cause any great catastrophe. So we've gone from 1.4 degrees of warming per 100 years to 0.1 degrees of warming per 100 years. The variable sunshine duration has accounted for 93% (1.3/1.4) of all warming trend that we have seen since 1951.

So therefore the warming that we are seeing, is by and large highly correlated with sunshine duration. So does this mean that clouds are the major cause of global warming? Well, probably not. In order to discuss why the variable "sunshine duration" has a major effect on temperature change, we have to look into how it is measured, and the trends of clouds in Australia. And that will be in the next post


Anonymous said...

Jones and Trewin, of the Bureau of Meteorology's National Climate Centre, authored a paper which discussed the influence of the ENSO on temperature.

They insist that a clear sky means higher maximum temperatures but also lower minimums.

It might be worth your while to examine the relationship between minimum temperature and sunshine.


John McL

Jonathan Lowe said...

yes obviously a clear sky results in higher day temps, and a clear sky in lower night temps, but the minimum temperature actually occurs during the day, so it would be interesting to see what effect that has.

Did Jones and Trewin simply discuss this or prove it with data?

Phil said...

Good work, Jonathan. This combined with cloud cover and min and mean data is definitely publishable (assuming climate politics don't block it.

Magnus A said...

What correlation can we ecxpect between mean temperatures (instead of maximum temperatures) and sun duration? Is there any calculations made somewhere?

Hubert wee said...

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Magnus Andersson said...
This comment has been removed by the author.
Magnus Andersson said...

Is this the max temperature for one station at one particulare day, or? What exactly is max temperature here?

I recognize a 1.6 degrees span between the lowest and highest max temperatures anomaly, so I guess you didn't counted the warmest day of the year. (That would have resulted in a greater span between high and low I guess.) Also it mustn't be the max temperatures of all days, because then I guess 1.6 degrees is a too large span.

So what is the max temperatures? A definition please.

slclemens said...

Thanks for this good against-the-grain science. Those of us in the fossil fuel industry have been arguing just this sort of thing for years. It's good to see the scientists finally catching up with us: the sun is the problem, not the fossil fuels.

Here's a tip of this Texas coal-burner's hat to you!

Jonathan Lowe said...

thanks slclemens,
Magnus, this is the average monthly maximum temperature anomalies. so for example for one station, the maximum temp on one day is 24 degrees. Over the 30 days the average max temp is say 22.5. from 1961 to 1990 the average maximum temp for that month is 21 degrees, so the anomality for that month for that year is 1.5 degrees.

Now thats only one month, one year, and one station. The analysis shown here for all the stations mentioned in each month going back past 1960 to about 1943.

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