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Mar 4, 2011

The Australian Academy of Science: what is climate change?

The period for estimating climate is usually 30 years or more, long enough to sample a full range of weather.

This is an extract from The Science of Climate Change — Questions and Answers, published by the Australian Academy of Science and distributed to members of parliament, every local government authority in Australia and every Australian high school, in August 2010. Crikey will be running a series of extracts, including canvassing common myths.

Climate change is a change in the average pattern of weather over a long period of time Climate is a statistical description of weather conditions and their variations, including both averages and extremes. Climate change refers to a change in these conditions that persists for an extended period, typically decades or longer.

Weather variables such as temperature and rainfall fluctuate naturally (see Box 1). These changes in weather from day to day, between
seasons, and from one year to the next, do not represent climate changes. The period for estimating climate is usually 30 years or more,
long enough to sample a full range of weather.

Climate can be defined for a particular place or region, usually on the basis of local rainfall patterns or seasonal temperature
variations. Climate can also be defined for the entire Earth. For global climate, a key variable is the average surface temperature.

Sustained and truly global changes in average temperature require some global heating or cooling influence such as variations in heat output by the Sun, changes to the Earth’s orbit around the Sun, changes in cloudiness, changes to the extent of ice on Earth’s surface, or changes in greenhouse gas concentrations in the atmosphere.

Identifying climate change that is truly global in extent requires simultaneous observations from a network of locations around the world (see Question 3). Such a network of instrumental observations has only been available since the second half of the 19th century. Climate changes that occurred before this time can be identified by reconstructing records from climate-sensitive indicators like ocean sediments, ice-cores,
tree rings and coral reefs.

Greenhouse gases play an important role in determining climate and causing climate change Greenhouse gases include water vapour, carbon dioxide (CO2), methane, nitrous oxide and some industrial gases such as chlorofluorocarbons (CFCs). These gases act like an insulating blanket, keeping the Earth’s surface warmer than it would be if they were not present in the atmosphere.

Except for water vapour, the atmospheric concentrations of all of these gases are being directly influenced by human activities (see Question
4). Once released into the atmosphere, many of these gases remain there for a long time: in particular, a significant fraction of CO2 emissions remains in the climate system for hundreds to thousands of years.

Water vapour is an important greenhouse gas but it is not like the greenhouse gases affected directly by human activities. Its concentration in the atmosphere is controlled by the climate itself, rather than by human activities.

Water vapour therefore reacts to, and amplifies, climate change caused by other factors (see Box 2 and Figure 1.1). The effects of changing greenhouse gas levels on climate can be distinguished from the effects of other factors such as changes to the Sun’s radiation. These different causes lead to different patterns or “fingerprints” in the resulting climate changes, which assist in identifying the cause of observed changes.

For example, increases in solar radiation would be expected to warm both the upper and lower parts of the atmosphere and result in days warming more than nights. On the other hand, increases in greenhouse gases would be expected to result in a cooling, not a warming, in the stratosphere (the layer of the atmosphere above 15 km elevation), and cause nights to warm more than days. The observed patterns of change
more nearly match those expected from increasing greenhouse gases.

There are close connections between global temperature, atmospheric water vapour, the extent of polar ice caps and levels of greenhouse gases (GHGs) in the atmosphere. When one of these is disturbed, the others react through processes that amplify the original disturbance until
a new, different climate equilibrium is reached.

In the glacial cycles over the past million years, the disturbance came from fluctuations in the Earth’s orbit around the Sun (grey box in upper diagram). This caused temperatures to change (green box), in turn inducing rapid changes in water vapour (left blue box), and much slower
changes in ice caps (right blue box) and greenhouse gas levels (orange box), which together amplified the temperature change.

In modern climate change, the disturbance comes from human-induced changes in atmospheric CO2 and other greenhouse gas levels (grey box in lower diagram). In both cases, the disturbance is amplified by similar reinforcing processes.

The Australian Academy of Science, which represents Australia’s foremost scientists, provides scientific advice to policy makers and promotes excellence in Australian science, has devoted considerable resources to untangling the science of climate change and presenting it in a simple and easily understood format.

The full report can be downloaded here for free.

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67 comments

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67 thoughts on “The Australian Academy of Science: what is climate change?

  1. Meski

    Water vapour is an important greenhouse gas but it is not like the greenhouse gases affected directly by human activities.

    A little disingenuous, human activities (eg large scale logging) affect the location of water vapour considerably.

  2. mattsui

    Water vapour eventually falls from the sky of it’s own accord….. GHGasses may remain up there indefinately.

  3. birdsnewworld

    “Water vapor is about half the present-day greenhouse effect”

    Even if you buy into the standard view that back-radiation is powerfully important, the above statement is an outrageous lie. Just incredible. I’d not expect this sort of rubbish from the most repulsive liars of Goddard or realclimate. What a far out statement. You see this constant lying isn’t going to stop until we start sacking people. This lie is second only to the USGS lie about volcanic CO2 emissions.

    Here’s the absorption-scattering spectrum just to take a look at things. And whereas the other alleged greenhouse gases are trace gases, water vapor is up at 1%. So there is the CO2 and its puny in three respects.

    1. There is so little of it. Barely enough for the plants to grow. No more than 390ppm if the compulsive liars monopolizing the measuring of it are to be believed. And of course you need 10 000 ppm just to get to 1%

    2. As you will see the regions of infra-red wavelengths that CO2 absorbs are tiny. Or skinny if you look at the graph.

    3. These regions, at most places and temperatures are usually pretty much saturated already by water vapor.

    So make no mistake about it. The report kicks off with a known and transparent lie. They get away with lying so much they must now be feeling deeply confident about it.

    http://1.bp.blogspot.com/_wXDx9TVRBL8/Sc6YF7FBeOI/AAAAAAAAA1w/9xNkidL2Kns/s400/Picture+e.png

  4. birdsnewworld

    “Water vapour eventually falls from the sky of it’s own accord….. GHGasses may remain up there indefinately.”

    Indefinitely? You cannot let these people stooge you fella. There’s a carbon cycle just like there is a water cycle. How is your comment relevant? Are you hoping that the extra CO2 will help us a little bit when the air is too cold to hold water vapor?

  5. birdsnewworld

    “Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface”

    Here wiki is talking about atmospheric composition. But what really counts is that its concentrated at the surface to mid-troposphere region. Thats why we can be quite sure that the scattering and absorption activities of water vapor will have a net warming effect. Because of its location. Water vapor has a warming effect for other reasons which I won’t go into. But at least with water vapor its very hard to make the case that the scattering and absorption component of what it does could ever be net negative.

    Whereas increases to CO2 levels at the surface slowly make their way up far above the troposphere. Where they would obviously have a cooling rather than a warming effect since they will scatter that part of the spectrum, and more than half of that scattering will make its way back out to space.

    This is a scandal that this claim has been made. I’ve taken all the names of the people involved in this sham organisation with such a high-fallooting name, and highlighted them on my blog. If they continue with this lie without retraction I MAY WRITE A LETTER.

    Well all jokes asides, I’ll try and alert the media even further than what I have already.

  6. Meski

    @Mattsui: Yes, but deforestation means that a larger percentage of it falls into the ocean, rather than on the land.

  7. birdsnewworld

    “@Mattsui: Yes, but deforestation means that a larger percentage of it falls into the ocean, rather than on the land.”

    But there has been massive regrowth of biomass. The problem is I cannot make a strong claim because I need a start and end date and its hard to get hold of the data. But over the last few decades, as troubling as the loss of biomass from the tropical areas has been, there has been massive reforestation in many first world areas and especially a lot of biomass growth in the far North.

  8. danr

    You can’t just treat CO2 as if it’s the only gas in the system.

    It is a complex interactive system and the reason Global Warming Protagonists wont discuss this is because it involves “real” science, not climate change science.

    Besides, heat from the sun liberates CO2 held in the ocean. This is an effect which swamps the “agw” effect.

    To top it all off, the biggest greenhouse gas is water vapour, against which effect CO2 is insignificant and man made CO2 effect barely noticeable within the error limits..

    Joke

    If Carbon pollution is CO2 then what is Hydrogen pollution.

    Yes, RAIN.

    If either was missing from our lives we would not be here. Both are life essentials.

  9. JamesH

    @ Danr

    “You can’t just treat CO2 as if it’s the only gas in the system. It is a complex interactive system and the reason Global Warming Protagonists wont discuss this is because it involves “real” science, not climate change science”.

    You have no idea what you are talking about. “Complex interactive system” is not a magic passphrase that protects you from science.

    “heat from the sun liberates CO2 held in the ocean. This is an effect which swamps the “agw” effect.”

    Heat from whatever source liberates CO2 from the ocean. If the heat of the atmosphere rises due to CO2, more CO2 will be released, which will cause more heat. This effect does not “swamp” but add to anthropogenic releases. The natural carbon cycle is balanced; we are unbalancing it.

    ” biggest greenhouse gas is water vapour, against which effect CO2 is insignificant and man made CO2 effect barely noticeable within the error limits.”

    Wrong. CO2’s absorbtion is not blocked by water vapour and is independently measurable and significant in size. Water vapour is a feedback not a forcing; water only remains resident in the atmosphere for a few days before condensing into rain, so it cannot raise the temperature for long periods as CO2, with a residency time of many years, can.

    “If Carbon pollution is CO2 then what is Hydrogen pollution”?

    Extremely dangerous.

    HTH.

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