Thursday, December 17, 2009

Analysis of Australian Temperature - Part 6 - Relationship between cloud cover and temperature

One would expect that a greater amount of cloud cover would result in a lower temperature and a lower amount of cloud cover would result in a greater temperature. We should previously that the amount of cloud cover in Australia has been decreasing since 1950, and we also showed that temperatures in Australia have been increasing, especially during the middle of the day, and temperatures have not been increasing during the night.

So what influence does the amount of cloud cover have on Australian temperatures during certain parts of the day and night? Shown below are the graphs of cloud cover anomalies verses temperature anomalies since 1950.

So what is quite clear from the above graphs is the clear relationship between cloud cover and temperature during the day. All relationships were significant apart from 9pm and Midnight, where no significant relationship was found. Interestingly, the relationship between cloud cover and temperature at 3am and 6am was positive, in that greater amounts of cloud cover was related to greater temperatures.

This is not that surprising, as cloud cover at night works as a blanket, helping to keep the temperature in. From 9am until 6pm, the relationship is undeniably negative, in that lower amounts of cloud cover is related to higher temperatures, and greater amounts of cloud cover is related to lower temperatures.

This is summarised in the graph below:

Here we can see that the strength of the relationship increases until Noon/3pm and decreases after/before this.

So it is clear that cloud cover amounts have a very strong relationship with temperature, as we previous hypothesised. As we showed previously that cloud cover levels in Australia, especially during the day, have been decreasing, what effect does this have on temperature?

Can we adjust the temperatures for this decrease in cloud cover? What effect will that have on the long term averages on Australian temperature? We will find this out in the next post.

Tuesday, October 13, 2009

Analysis of Australian Temperature - Part 5 - Cloud cover over time

What effect does cloud cover have on Australian temperatures? Has cloud cover increased or decreased over time? Obviosuly, and especailly during the day, the more clouds that abound, the lower the temperature, and conversely the less clouds during the middle of the day, the higher the temperature.

When the sun is set, the relationship is a little more dubius. Cloud free summer days will have hotter nights if there is cloud cover, however the more days that are cloud free, the higher the atmosphere will be to start off with.

Either way, have Australia’s cloud cover increased or decreased over time? Fortunately, the Australian Bureau of statistics provides good data on this, and we are even able to measure the level of cloud cover as a variable over certain times of the day.

The following are Australia’s cloud cover anomalies from 1950 until current. Note that from about 1996 to current for midnight, and from 2000 to current for 3am, limited data was available.

SO what does this show? Well quite clearly it shows no major change in cloud cover at midnight, but from then on the level of cloud cover decreases dramatically overtime, reaching its decreasing trend peak at 3pm, and then the trend increases, where it actually has a positive value at 9pm, before stabilising.

Take a special look at the last five years of cloud cover from 9am to 6pm. These are dramatic negative cloud cover anomalies, and if you remember what the temperatures looked like during these last few years at the same times, perhaps there is a strong relationship between the two.

It is interesting, that during the heat of the day at 3pm, the cloud cover trend is at its decreasing peak. This is interesting. Scientists do not know much about cloud cover and the reason why its levels vary. However quite clearly here, a pattern arises where the level of cloud cover has decreased over time up until 3pm, before increasing back to a level state. This is highlighted by the graph below.

What happens to Australia’s temperature over time, when we account for the changing values of cloud cover? We will find out in the next article.

Friday, June 05, 2009

Analysis of Australian Temperature - Part 4 - Summer/Winter Effect

If CO2 was the major cause of global warming, then we should see a constant increase of temperature in summer as in winter. The blanket of Co2 should increase the temperature constantly over the year. Likewise it should increase the temperature constantly over the day and night, however I have showed previously that this does not happen.

So are summer and winter temperatures in Australia in increasing at around the same rate? Even according to the Australian Bureau of Meteorology this isn't quite happening. Summer temperatures are increasingly, well, slightly as shown here, whilst winter temperatures are increasing at a rapid rate as shown here.

One could argue here that this occurs mainly because of the different tropical climates that Australia has, and indeed this may well be the case. As northern Australia's summer temperatures do not increase at all, whilst their winter does. And conversely, southern Australia's summer and winter temperatures seem to be increasing. I'm not 100% sure why the tropics summer tends not to increase in temperature. It might be a threshold (its damn hot up there already in summer), or it might be something to do with the humidity. I'm also not sure why the BOM only have a trend going back to 1950 on these graphs, when there clearly is more data available.

In fact, the more data that they could use is that of shown below which compares the summer and winter temperatures based on the standard times of midnight, 3am, 6am, 9am, noon, 3pm, 6pm and 9pm. We have showed previously how the minimum temperature is not a good indication of long term trends at night, so the analysis to come should be interesting.

If CO2 were the major cause of global warming, then we should see a relatively constant increase in temperature in summer when compared to winter across all the times given above. Lets see if we do:

So what do we find? We find that there is no difference between summer and winter trends at night (namely Midnight, 3am and 6am). This is no surprise as we previously found that overnight temperatures have hardly increased over the past 60 years. However something happens at 9am which is quite drastic. All of a sudden summer temperatures at 9am are decreasing at such a rate when compared to winter temperatures.

What does this mean? It means basically that at 9am winter temperatures are increasing quite drastically when compared to summer. This trend is not small either, it is at a rate of 3.1 degrees per 100 years, more than 3 times the world average. Similar trends, but decreasing in nature occur at Noon and 3pm, where as at 6pm and 9pm the trend is reversed.

Interestingly, at 6pm and 9pm the sun will generally still be in the sky and have an influence in summer in Australia, but not in winter. Perhaps this is the reason why summer temperatures are increasing at a greater rate than winter temperatures at this time?

Either way, the trends are extremely strong and disturbing. If CO2 were the major cause of global warming, then we should see a constant trend throughout the day, and when comparing summer and winter trends throughout the day. We see none of this, but rather the opposite.

Perhaps Australia's Cloud Cover levels could be a major contributor to the increasing temperatures that Australia is recording? We shall look at this in the next post.

Monday, May 04, 2009

Australian Bureau flips over Antarctica

As reported in the Australian

THE Bureau of Metereology has backed down from a claim that temperatures at Australia's three bases in Antarctica have been warming over the past three decades.

A senior bureau climatologist had accused The Weekend Australian of manufacturing a report that temperatures were cooling in East Antarctica, where Australia's Mawson, Davis and Casey bases are located.

The trend of temperatures and ice conditions in Antarctica is central to the debate on global warming because substantial melting of the Antarctic ice cap, which contains 90 per cent of the world's ice, would be required for sea levels to rise.

While calvings from ice shelves in parts of West Antarctica have generated headlines, evidence has emerged that temperatures are cooling in the east of the continent, which is four times the size of West Antarctica.

Contrary to widespread public perceptions, the area of sea ice around the continent is expanding.


My analysis here at Gust of Hot Air has easily shown this. Here is my previous analysis of temperatures at Mawson, Antarctica. And for want of comparison, Macquarie Island, which is situated half way between Australia and Antarctica.

Thursday, April 16, 2009

Analysis of Australian Temperature - Part 3

For all new readers, please read Analysis of Australian Temperature - Part 1 and Part 2 first.

Previously we found that temperatures overnight in Australia are staying relatively steady over the years despite the minimum temperatures increasing. Temperature trends over time suddenly rose when the sun made an appearance, increasing at a greater rate until the middle of the day and then fading away. A case for the sun can be easily argued here.

This can be backed up even more when looking at time based differences over the years. Shown below are the differences in temperature trend over the years for two neighbouring times.

The above graphs show us a few things. Firstly that there is no difference in temperature trends over time at night from 9pm to 6am. Temperatures are steady over time. Then suddenly at 9am we see a sudden increase in temperature. Temperatures remain steady throughout the day (despite a seemingly seasonal trend?), but at 6pm the temperature drastically decreases when compared to 3pm. All this could have been deduced from the previous graphs.

But what happens if we look at the differences in trends from summer and winter?
I will look into this further and in a lot more detail in the next post.

Wednesday, April 08, 2009

Analysis of Australian Temperature - Part 2

For all new readers, please read Analysis of Australian Temperature - Part 1 first.

Part 2:

What is interesting in the analysis done in Part 1, might not have been that 44% of all warming in Australia is accounted for, simply by a better mathematical method of analysing the data, but rather the variations in the temperature throughout the day as shown below:

Why is it that we are seeing a significant warming trend between the hours of 9am and 3pm, and a smaller increase in other times? Surely, if CO2 were the principle mean of global warming, then we should see a constant increase amongst all times. This clearly is not the case in the analysis of Australian temperatures.

We can look even closer at Australian time based temperatures by comparing their anomalies over time as compared to the maximum and minimum temperatures. If global warming has been by and large been a result of an increase in CO2 emissions, then we should have a steady increase when compared to maximum and minimum temperatures over time. This is what we find below:

What we find in the above is something quite extraordinary. For 9am, noon, 3pm, 6pm and 9pm there is little trend. This indicates that temperatures at these times have increased at around the same rate as the minimum temperature. Readers will note however a large increase in the last 10 years of differences in temperature between 9am and the minimum.

However for midnight, 3am and 6am, we see a very strong decreasing relationship. This indicates that the minimum temperature has increased at a significant rate when compared to these temperatures. Some readers will say that this is understandable considering the analysis done in part 1, however it is highlighted here for significantly.

It seems, that the minimum temperature is more strongly related to the temperature in the middle of the day than at night. Too may times, people quote minimum temperature trends as having something to do with overnight temperatures, when we clearly show here, and the fact that the minimum rarely occurs at night, that this is not the case.

Put frankly, the minimum is a poor measure of overnight temperatures, and its trend has more to do with day temperatures than night. And what of maximum temperatures? An analysis of time vs maximum temperatures is shown below.

Whilst the above graphs show that maximum temperatures have increased at a greater rate over time when compared to midnight, 3am and 6am temperatures, this was expected. What was not expected is the strong negative relationship between maximum temperatures and time based temperatures during the day. In particular 3pm. Maximum temperatures are shown here to be increasing at a lot larger rate over time when compared to 3pm (and other day temperatures).

This is strange, as we would expect the maximum temperature to be reached between noon and 6pm depending on various aspects, especially the season. What this indicates therefore, is that during the day, Australia is heating up at a greater rate per hour, reaching a peak temperature and then falling in temperature at a greater rate per hour.

One could argue that Co2 could not be the cause of this. The carbon blanket should increase temperatures steadily throughout the night and day at a relatively constant rate. However, what we are seeing here is minimal increases at night, and then steady increase and then decreases during the day, the rate of change of this increase and decrease during the day increasing over time.

What could cause this? Well in Part 3, we will compare time based temperatures as well as look at temperature trends based on season (summer, winter).