It emits no more CO2 than the thing being composted soaked up when growing. So it will emit less than the amount the mushrooms absorbed. This is the cycle of life. This is not a problem.
The problem is when you emit CEO that has been absorbed over hundreds of millions of years and fossilized in oil and gas all within 100 years or so.
The problem is when you emit CEO that has been absorbed over hundreds of millions of years and fossilized in oil and gas all within 100 years or so.