I always like debates over climate sensitivity, not only the discussion on negative or positive feedback, but also the idea that if scientist's predictions are correct and we have positive feedback, then this will have consequences.
When I write consequences I don't mean FUTURE consequences, BUT for the reconstruction and interpretation of old data. If they assume a warming of 2 °C due to rising ppm in CO2, then in the past with half the ppm of today, we should have seen half the warming of today. However, this underpredicts temperature data, though I'd like to see science papers on this one. I believe it is a side issue that has been ignored, but could prove that feedbacks are overestimated.