I remember when I first heard of these certificates there was a scandal
that some were not genuine. It appeared that Russians and others simply
printed them and sold them.
They are now a multi billion dollar argument in the election.

They have value because companies can buy them instead of reducing
their CO2 emissions. There is a market that buys & sells the
certificates and so establishes their value.
The present price is I believe around $60.

My interest has arisen because I wondered what would happen if a
company bought one million dollars worth to offset their CO2
emissions and so avoid expensive plant upgrades.
Then one day the scientific consensus on global warming changed and it
was decided that the earth was not warming but some cooling was evident.

The value of the certificates would disappear. Would the government
pay back the company their one million dollars ?
At present the government and opposition are arguing about B$40 & B$60

Genuine or not. Does this trading actually make any difference to the amount of carbon dioxide in the air: say, will we notice a drop off in the greening of the world and a loss of production that the increase in CO2 has brought about?

Bazz once action starts there will be no turning back
The buying and selling of such things, in my view tries to say it is ok to pollute your own country and help keep others clean

Bazz,
The thing about scientific consensus is that it's driven by evidence. Right now there's an enormous amount of evidence of warming. If cooling is observed we'd look at what's causing it, but the scientists wouldn't blindly claim the warming trend had stopped even if the bloggers did.

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ttbn,
In isolation, the trading wouldn't make much difference, But when combined with countries committing to reduce their carbon footprint, it makes a lot of difference as it greatly reduces the cost of doing so.

Any evidence that the CO2 increase has actually increased agricultural production? I know there are instances where it's reduced the demand for water, but AIUI these have not been sufficient to counteract the decrease in rainfall in those places.

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Belly,
When the effects of this pollution are global not local, the location where the pollutant is being released into the atmosphere doesn't matter.

Aiden no defense know and knew that but feel more comfortable if we each clean up our own country or help other do so

"In isolation, the trading wouldn't make much difference, But when combined with countries committing to reduce their carbon footprint, it makes a lot of difference as it greatly reduces the cost of doing so".

Fact: Australia is naively working " in isolation" while the biggest polluters like China and India are going full steam ahead, building coal-powered electricity generators non-stop, taking our industries, and sniggering up their sleeves at us. Yes. There is evidence of greening and increased production.