Data Contradicts Connection Between Earth's Tilt and the Seasons

***The following is a satirical argument intended to highlight some basic errors often made in the climate change debate. Also, I want to show how easy it can be to fool ourselves with real data. The subjects that are touched on are 1) signal-to-noise ratio issues in the Earth's climate system (also discussed here and here, for example) and 2) the fallacy of inferring causality from correlation without evoking physics (also discussed here and here). Those who follow the global warming debate will immediately recognize the similarity to arguments that short-term cooling during a CO2 increase disproves human-caused warming.***

For years we have been told that the Earth's tilt and the associated changes in incoming solar radiation are the cause of the seasons. Scientists have claimed that it is "settled science" that during spring, the day length increases and the sun gets higher in the sky at noon. According to the theory, this should cause the Northern Hemisphere to warm from Feburary through April. However, if this science is so "settled", then why is it easily refuted with empirical evidence?

I live in San Jose, California. The blue curve in figure 1 shows the daily high temperature that we experienced between February 22nd and April 7th. I have also plotted the amount of daylight for each date in question. Notice that we experienced an overall downward trend in temperature over this time period while the length of daylight steadily increased. This is precisely the opposite of what the 'tilt theory' of seasons claims. The data proves the theory invalid!

Figure 1 – Daily high temperature versus length of day in San Jose, California from February 22nd to April 7th 2012.

So if the day length does not have an effect on local temperatures what does? Figure 2 shows the same temperature data displayed in figure 1 but with the daily high sea level pressure overlaid in red. Immediately we can recognize a strong relationship between these two variables. As sea level pressure decreased over this time period, it caused temperature to do the same.

Figure 2 – Daily high temperature versus daily high sea level pressure in San Jose, California from February 22nd to April 7th 2012.

The conclusion is clear. The tilt of the Earth relative to the sun does not control local temperature variations nor does it cause seasons. Instead, local sea level pressure is the cause of seasonal changes in temperature.

***People with some knowledge of meteorology and the Earth's seasons will find the above argument ridiculous. However, if there was some political benefit from confusing the issue of why the Earth experiences seasons, I am almost certain that you would see arguments like this all over the blogosphere.

For those who do not immediately see why the above arguments are incorrect remember a couple points:

1) In order to see the effect of the Earth's tilt on San Jose weather; you need to investigate a time period longer than ~6 weeks. To see when the signal becomes apparent through the weather noise see this graph.

2) Daily high temperature and daily high sea level pressure are indeed highly correlated variables. This is because the ideal gas law shows that 'all else being equal', they must be correlated. Furthermore, from a synoptic meteorology perspective, high pressure systems are associated with clear skies and more incoming solar radiation. The problem is that this has nothing to do with the cause of seasons. For instance it can't explain why our seasons follow a 12 month cycle. Instead this relationship is only of real consequence for short term variability in local weather.***

Posted by ptbrown31 on Thursday, 12 April, 2012

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