The phenomenon that is being described where melting ice causes the release of CO2 into the atmosphere seems to have been known to climate scientists, though I don't know whether it has been included in climate change models.
There is a great talk (video online here: https://www.facebook.com/WoodsHoleOcean/videos/1015459031268...) by Richard Alley where exactly this phenomenon is mentioned (see Q&A at ~50:55 in the video, though I highly recommend watching the whole thing).
There is a great talk (video online here: https://www.facebook.com/WoodsHoleOcean/videos/1015459031268...) by Richard Alley where exactly this phenomenon is mentioned (see Q&A at ~50:55 in the video, though I highly recommend watching the whole thing).