Although we are confident that adding greenhouse gases to the atmosphere will cause the planet to warm, exactly how much we will warm is uncertain (the IPCC likely range for a doubling of atmospheric CO2 is 1.5oC to 4.5oC). A major reason for this uncertainty is that we don’t know what clouds will do as we warm. Low level clouds act to reflect incoming solar radiation, cooling the planet. High-level clouds are very cold and hence radiate very little energy into space, but block some of the radiation coming from the surface; they act to heat the planet.
Therefore, estimating how much we will warm requires understanding how low-level and high-level clouds will change. It’s possible that these changes could act to reduce how much we warm (cloud feedbacks could be negative). Alternatively, these changes could amplify the warming (cloud feedbacks could be positive). Do we have some idea of what is likely? Yes, we do, but rather than me telling you what it is, you could watch Kate Marvel’s recent TED talk. Kate explains it much better than I possibly could.