In today’s climate models, volcanic eruptions are thought to be a major negative forcing (they have to be, to counteract the over-egged positive forcing attributed to CO2), but the ‘projections’, ‘forecasts’, ‘scenarios’ (anything but predictions!) don’t include any volcanic eruptions.
That being the case, why would we take any notice of model output which ‘projects’ large warming in the future?
Judith Curry:
Under the RCP8.5 scenario, the CMIP5 climate models project continued warming through the 21st century that is expected to surpass the ‘dangerous’ threshold of 2°C warming as early as 2040. It is important to note that the CMIP5 simulations only consider scenarios of future greenhouse gas emissions – they do not include consideration of scenarios of future volcanic eruptions…