|1. All data used on this web page is available from the Australian
Bureau of Meteorology at this
|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.
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.
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)
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.
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.
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!
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 ?
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?
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.
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
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
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
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
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
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