" Warmer Temp = Less Cooling From Volcanoes " Topic

Impact of global warming on the rise of volcanic plumes and implications for future volcanic aerosol forcing
By Aubry et al (2016), Journal of Geophysical Research: Atmospheres

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Volcanic eruptions have a significant impact on climate when they inject sulfur gases into the stratosphere. The dynamics of eruption plumes is also affected by climate itself, as atmospheric stratification impacts plumes height. We use an integral plume model to assess changes in volcanic plume maximum rise heights as a consequence of global warming, with atmospheric conditions from an ensemble of global climate models (GCM), using three representative concentration pathways (RCP) scenarios. Predicted changes in atmospheric temperature profiles decrease the heights of tropospheric and lowermost stratospheric volcanic plumes and increase the tropopause height, for the RCP4.5 and RCP8.5 scenarios in the coming three centuries. Consequently, the critical mass eruption rate required to cross the tropopause increases by up to a factor 3 for tropical regions, and up to 2 for high-latitude regions. A number of recent lower stratospheric plumes, mostly in the tropics (e.g., Merapi, 2010), would be expected to not cross the tropopause starting from the late 21st century, under RCP4.5 and RCP8.5 scenario. This effect could result in a ≃5 − 25% decrease in the average SO2 flux into the stratosphere carried by small plumes, which frequency is larger than the rate of decay of volcanic stratospheric aerosol, and a ≃2 − 12% decrease of the total flux. Our results suggest the existence of a positive feedback between climate and volcanic aerosol forcing. Such feedback may have minor implications for global warming rate but can prove to be important to understand the long-term evolution of volcanic atmospheric inputs.

TL:DR, warmer atmospheric temperatures means that you need a larger volcano explosions to get sulfur compounds into the troposphere. This will slowdown the cooling effect of volcanoes since the sulfur will stay lower in the atmosphere, and thus get washed out with regular rain within weeks rather than years.