Tuesday, December 18, 2007

Clouds and Global Warming

Clouds have often been a problem for climate scientists. Global dimming or global brightening? Wikipedia states that

Feedback effects due to clouds are an area of ongoing research. Seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect; seen from above, clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Whether the net effect is warming or cooling depends on details such as the type and altitude of the cloud. These details are difficult to represent in climate models, in part because clouds are much smaller than the spacing between points on the computational grids of climate models.

Recently when questioning embers of the CSIRO as to why north-west Australia has seen a cooling trend in the last 50 years, he replied that it was due an increase in clouds in that area, possibly, due to an increase in aerosol usage in Asia.

And increase in clouds in that area made sense. IT has, after all, seen a massive increase in rainfall in the last 20 years, so one would also expect an increase in cloud activity. I asked him if eastern Australia is warming up due to less clouds, as the east also, has received less rain. His response was it could have a small minor effect, but that greenhouse gases were shown through models to be the major cause.

I needent have asked.

So, is what he says is true? Are we seeing more clouds in the north west, and no difference in clouds in the east? One would expect more or less clouds would cause an decrease and increase in temperature. How much of an effect it has we shall see. Luckily, the Australian Bureau of Meteorology has the data so we can look into it.

However, the data is not as extensive as temperature based data, and to get a good sized data range, we've had to include stations that are classified as urban.

The following stations have data on "sunshine duration" that go back to at last 1961, (the standard of comparison over years in climate data is from 1961 to 1990):

GILES METEOROLOGICAL OFFICE
DARWIN AIRPORT
TENNANT CREEK AIRPORT
ALICE SPRINGS AIRPORT
WOOMERA AERODROME
CEDUNA AMO
MOUNT GAMBIER AERO
KAIRI RESEARCH STATION
WALKAMIN DPI
TOWNSVILLE AERO
BRIAN PASTURES
COFFS HARBOUR MO
WILLIAMTOWN RAAF
SCONE SCS
EAST SALE AIRPORT
HOBART AIRPORT
GROVE (COMPARISON)
STRATHGORDON VILLAGE
NORFOLK ISLAND AERO
DAVIS
MAWSON
MACQUARIE ISLAND

The placements of the stations are shown at this link.


Unfortunately, Western Australia is not very well surveyed, with only one station at Giles having accurate and lengthy data on sunshine duration. Similarly country Queensland and New South Wales have gaps. Conversely Tasmania and Cairns are over sampled.

But the purpose of this exercise is not to formulate whether Australia is warming or cooling based on the stations, but rather what relationship does sunshine duration have on temperature. If we account for sunshine duration, do we still see an increase in temperature over the past 50 years?

But to start off with, we will look into if sunshine duration, in the stations provided has increased or decreased or stayed around the same in the past 50 years. And this will be in the next post

8 comments:

Phil said...

Unfortunately, Western Australia is not very well surveyed, with only one station at Giles having accurate and lengthy data on sunshine duration.

WA is only 2% of the Earth's land surface. Why worry about it?

Anonymous said...

Hi Jonathon,

I already extract ISCCP data for many regions (see this page>here) so please respond to this and tell me what region(s) of Australia you would like to see.

cheers

John McLean

PS. 1 - I'm posting under "anonymous" because I can't remember my name and password.

Selwyn said...

I was wondering whether the comment on behaviour in the east was based on the belief that cloud coverage had not changed there or the belief that eastern clouds were diffrent from westen clouds.

Jonathan Lowe said...

not sure selwyn, but no better way to prove or disprove it through statistics as we shall see soon.

Anonymous said...

Let's see if I've got this right.

More clouds = cooler.
Less clouds /= warmer.

CO2 heating is only occuring over the East of Australia and not the North West?

Robert Wood
Ottawa, Canada

Jonathan Lowe said...

the north west of Australia cooled over the last 50 years, however everywhere else (north, east, south, south-west etc.) warmed

Jonathan Lowe said...

Hi John McLean,
nice website with good data and analysis. I do actually have all the data the BOM have for cloud cover, which I believe has shown to be relatively consistant over the years with no obvious trend.

The variable Sunshine duration, is measured differently which you might know of.

I would interested in having n informal chat to you about this type of thing. If you are interested, let me know your email or I'll let you know mine and we'll have a informal chat

Cheers
Jonathan

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