Australia's Changing Climate
1.  All data used on this web page is available from the Australian Bureau of Meteorology at this page.
2.  Temperatures are shown as anomalies and these represent the variation in actual values from the mean values during the period 1961-1990.
3.  Click on the small graphs to display a larger graph in a new window.

To listen to some Australian politicians one would imagine that rainfall has dropped dramatically - but that is not the case.
Annual rainfall This graph shows that rainfall increased around 1974 and that the current average exceeds 500mm per year when the old average was about 460mm. Rainfall is not decreasing in Australia and that is despite a series of El Nino induced droughts in the 1990s and in 2003.
Seasonal rainfall The breakdown into seasons shows that the greatest increase in rainfall occurs during summer. This graph indicates that average winter rainfall is unchanged, autumn and spring rainfall has increased slightly and average summer rainfall has increased dramatically.  The trend line for winter rainfall is almost flat, neither an increase or a decrease, but the trend-line for summer rainfall is an increase of almost 5mm per decade (ie. 50mm per century, or almost 2 inches)
WInter rainfall SW WA Various Australian organisations are saying that rainfall in south-western Western Australia has declined in recent years and that this is due to global warming. Nonsense! The decline in rainfall really occurred in the late 1960s.  More recently there has been a slight recovery which lasted until a recent drought.

Annual Temperature (and Carbon Dioxide)
Carbon Dioxide levels The commonly accepted graph of the annual average level of carbon dioxide appears at left. There is some doubt as to whether the levels found in ice cores (dark line) actually append neatly to the observed levels (orange line) because the original calculation for ice cores indicated that the end date was about 1880 and not 1953.  Whether the date is correct doesn't really matter because this is what the proponents of Anthropogenic Global Warming (AGW) would have us believe, just as they encourage us to believe that temperatures rose as a consequence of the increase in carbon dioxide.
Annual mean temperature Australia's mean annual temperature is shown at right but it looks nothing like the graph of carbon dioxide levels. Australian temperatures started rising about 1947 but have shown a mixture of increases and decreases since that date. The major decline about 1978 put us back to almost where we had started from but carbon dioxide levels did not show a similar decline. Note also that some dramatic differences (about 1 degree) have occurred in successive years and yet this is rarely mentioned, save of course for a scare in the late 1970s that we might be heading for an Ice Age!
Max and min temperatures But look at the difference between the changes in maximum and minimum temperatures!  Minimum temperatures have risen since 1948 (before carbon dioxide levels increased) but maximums have only really risen since 1976 (long after carbon dioxide levels rose). Carbon dioxide caused these temperature rises ? Give me a break! Does this look anything at all like the graph of carbon dioxide levels ?

Seasonal Variations
Summer and Winter temperatures have varied in quite different ways since 1950 with winters warming more than summers.  Again, if carbon dioxide is steadily increasing then why should we be seeing very different situations in the two seasons?
Min and max temperatures in Winter Winter maximum and minimum temperature anomalies show substantial differences except for a brief period from about 1960 to 1975. In the last few years there has been a significant difference and the high maximums and lower minimums are probably related to El Nino conditions.
Min and max temperatures in Summer Summer maximum and minimum temperature anomalies have generally been similar to each but with a greater difference in the high-rainfall years of the mid 1970s, when the maximums were considerably lower than usual, and in the 1990s when minimum temperature anomalies were noticeably greater
Diurnal Temperature Range (DTR) For Australian conditions the Diurnal Temperature Range (DTR) is a good indicator of the extent of cloud (according to the IPCC, correlation parameter r  is 0.90) and the differences between Summer and Winter are dramatic.

A low DTR (< 0.0) is indicative of significant levels of cloud cover and a high DTR (>0.0) indicates a reduced level of cloud cover.  The decline in summer DTR (red line) means that summer cloud cover has been steadily increasing.  The winter DTR has been more variable with increasing DTR indicating reduced cloud cover and decreasing DTR which indicates reduced cloud cover.  Most recently the winter cloud cover has dramatically reduced, probably as a consequence of drought conditions.

Cloud and Temperature
The idea that carbon dioxide is the cause of climate change is hopelessly weak. The graphs in the last section showed no correlation between temperature and carbon dioxide. A far stronger argument can be presented for cloud cover to be a major influence.
Estimated and observed cloud The cloud cover can be estimated from the Diurnal Temperature Range (DTR) and this checked against the observed amount of cloud in the period 1957-1998.  From this we find a very close correlation between cloud cover and (3.135 - DTR) and we can use this to estimate cloud outside that 57-98 period.

This estimate matches reasonably well to the annual mean rainfall. (Rainfall must have associated cloud but extensive cloud cover is no guarantee of rainfall.)

The influence of the cloud can only be guessed at because the amount of radiation being blocked by cloud depends on the geometry of the situation (a combination of the time of day and season) as well as the density and height of the cloud.

Estimated cloud + temperatures When the 5-year running average of cloud cover is plotted against the annual maximum and minimum temperature anomalies two factors become apparent. (1) Increased cloud cover correlates with a reduction in maximum temperatures. This is explained by a reduction in solar radiation reaching the earth's surface. (2) Increased cloud cover also generally correlates with an increase in minimum temperatures. This is explained by cloud trapping heat - particularly at night - and preventing its escape into space.

Note that in Australia the amount of cloud increased in the mid 1940s and has generally correlated well with minimum temperature, and it is rising minimum temperatures that have forced the increase in mean temperatures, and we call that increase in mean temperature "warming".

Is cloud a cause or consequence of warming ?  There are indications that it may be both because it might amplify other effects.  Clouds may cool or warm and and which action takes place at a specific time depends on a host of factors which ultimately reduce to the direction of the radiation (solar radiation strikes the earth but night-time radiation goes from the earth into space) and how much radiation is being blocked.  These are influenced by latitude, season, time of day, cloud density, cloud height, the number of cloud layers and so on.

As we've seen, minimum temperatures have increased more than maximum temperatures while cloud cover has increased and so it appears that night-time cloud is playing a major role.

Scientists have also confirmed that water vapour is a far more significant warming agent than carbon dioxide because there is about 80 times more water vapour than carbon dioxide in the atmosphere and water molecules absorb about twice as much energy as carbon dioxide.

In case you are wondering, most of the world has seen an increase in cloud in the last 20 or 30 years. Whether this increase in cloud is natural or anthropogenic (from aerosols, jet-aircraft and steam discharge from factories and buildings) is uncertain.

More information and links to details about each Australian state
will be added when time permits

Last update: 28 Dec 2004