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Geofysisk institutt

GFI/BCCR Seminar: A role for volcanoes in future climate assessments

Ingo Bethke (Uni Research Climate)

A role for volcanoes in future climate assessments

Abstract

Episodic volcanic activity has been an important driver of past climate variability and is expected to continue to shape future climate despite human influence. Due to the unpredictable nature of volcanic eruptions, effects of volcanoes have so far been neglected in future climate simulations which form the basis for climate impact assessments. In this talk, I will address how the consideration of plausible volcanic activity is likely to affect the outcome of probabilistic climate projections. To this end, we constructed a large number of plausible volcanic forcing futures that are based on proxy-recorded volcanic activity of the last 2,500 years. We applied these forcing futures in the Norwegian Earth System Model and performed a 21st Century simulation ensemble that we compared to a reference ensemble with zero volcanic forcing. I will show that the inclusion of volcanic activity changes important aspects of our 21st Century climate projections. Most notably, the distributions of climate means and trends become wider on a range of time scales, because volcanic activity inflates the level of natural climate variability. As a result, the probability for simulating future occurrences of decadal-scale "warming pauses" increases by more than 50% in our model. The consideration of volcanic forcing uncertainty has thus particular implications for climate adaptation decisions and risk assessments, where the focus often is on the spread and tails of distributions. Impacts on long-term climate trends are less pronounced and can partly be captured by using time-invariant background forcing. Our study concludes that including plausible volcanic uncertainty is both possible and important in future climate assessments.