They say the carbon dioxide level is too high. So the first solution is to remove some carbon dioxide from the air and put it in large tanks of various sizes.
The second solution is to stage the tanks in strategic locations near forest and airports. In the event of a forest fire, at the correct time, release the carbon dioxide into the fire. Some tanks could be airlifted into location before being discharged.
This would replace the normal air around the fire and would reduce the burn rate, or maybe extinguish the fire entirely.
As a side note, it would greatly reduce the exhaust from the burning wood, which produces more smog than any fossil fuel. This smog, of course, contains carbon dioxide and carbon monoxide.
I doubt anyone would be interested in using such a method. The expense would be far greater than the benefit. The forests are not worth that much. Besides, if it worked, it would take an argument from both the tree hugers and the climate changers.
Maybe a better way would be to remove some of the trees each year, which would decrease some of the fuel. Moreover, the trees that are removed could be put to good use, far better use than if they were reduced to ashes.