Quantifying the impact of early 21st century volcanic eruptions on global-mean surface temperature

Despite a continuous increase in well-mixed greenhouse gases, the global-mean surface temperature has shown a quasi-stabilization since 1998. This muted warming has been linked to the combined effects of internal climate variability and external forcing. The latter includes the impact of recent increase in the volcanic activity and of solar irradiance changes. Here we used a high-resolution coupled ocean-atmosphere climate model to assess the impact of the recent volcanic eruptions on the Earth's temperature, compared with the low volcanic activity of the early 2000s. Two sets of simulations are performed, one with realistic aerosol optical depth values, and the other with a fixed value of aerosol optical depth corresponding to a period of weak volcanic activity (1998-2002). We conclude that the observed recent increase in the volcanic activity led to a reduced warming trend (from 2003 to 2012) of 0.08 degrees C in ten years. The induced cooling is stronger during the last five-year period (2008-2012), with an annual global mean cooling of 0.04 degrees C +/-0.04 degrees C). The cooling is similar in summer (0.05 degrees C +/- 0.04 degrees C cooling) than in winter (0.03 degrees C +/-0.04 degrees C cooling), but stronger in the Northern Hemisphere than in the Southern Hemisphere. Although equatorial and Arctic precipitation decreases in summer, the change in precipitation does not indicate robust changes at a local scale. Global heat content variations are found not to be impacted by the recent increase in volcanic activity.