The trial against the mine, which environmental group Coast and Country have pursued, has been continuing for weeks and today the Queensland Land Court will hear from a climate change expert about how the project will affect the climate.
350.org Galilee Basin campaigner Janelle Rees said their group wanted to show support for the climate change evidence.
She said the black balloons represented the amount of carbon which the Carmichael Mine would produce.
"The main concern is that most experts are saying that 80% of the world's fossil fuels need to stay in the ground," she said.
"And when you're talking a mine the size of the Carmichael Mine it could be up to seven times the size of Sydney Harbour, this is going to lead to unstoppable climate change."
Ms Rees said while the rest of the world continued to make progress in addressing climate change, Australia was going backwards.
"The biggest concern is we need to leave this in the ground," she said. "This mine isn't going to do that and we need to make a transition to renewables to other sources of economic development outside the fossil fuel industry."
Ms Rees fears burning coal from the Carmichael Mine would push the world over the two degree warming, which politicians around the world were working towards.
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