The climatic effects of the direct injection of water vapour into the stratosphere by large volcanic eruptions
- ISSN: 1680-7316
- DOI: 10.5194/acp-9-6109-2009
We describe a novel mechanism that can significantly lower the amplitude\nof the climatic response to certain large volcanic eruptions and examine\nits impact with a coupled ocean-atmosphere climate model. If\nsufficiently large amounts of water vapour enter the stratosphere, a\nclimatically significant amount of water vapour can be left over in the\nlower stratosphere after the eruption, even after sulphate aerosol\nformation. This excess stratospheric humidity warms the tropospheric\nclimate, and acts to balance the climatic cooling induced by the\nvolcanic aerosol, especially because the humidity anomaly lasts for a\nperiod that is longer than the residence time of aerosol in the\nstratosphere. In particular, northern hemisphere high latitude cooling\nis reduced in magnitude. We discuss this mechanism in the context of the\ndiscrepancy between the observed and modelled cooling following the\nKrakatau eruption in 1883. We hypothesize that moist coignimbrite plumes\ncaused by pyroclastic flows travelling over ocean rather than land,\nresulting from an eruption close enough to the ocean, might provide the\nadditional source of stratospheric water vapour.