Attribution Assessment for Recent Climate Extremes: Record Annual Mean Warmth during 2014 and the 2011-14 California Drought

Jonghun Kam

Cooperative Institute for Climate Science, Princeton, NJ, 08540 Geophysical Fluid Dynamics Laboratory/NOAA, Princeton, NJ, 08540

Monday, Feb 08, 2016, 2:00 pm
DSRC Room 1D-403

Abstract

Abstract

In this seminar, I will present an attribution assessment study for recent climate extremes using multiple data sources (e.g. observational data, reanalysis product, and global climate model output). The first part of the seminar will introduce the record annual mean warmth during 2014 and its attribution to anthropogenic influence. Observational surface temperature data show that during 2014 record annual mean warm anomalies occurred in regions of Europe, the eastern North Pacific (EPac), and the western North Atlantic (WAtl). According to CMIP5 models, the risk of record annual mean warmth in European, EPac, and WAtl regions—as occurred in 2014—has been greatly increased by anthropogenic climate change. Additionally, uncertainties of the anthropogenic influence on the risk of extremes are evaluated by comparing the estimates of fraction of attributable risk from different climate models. The second part of the seminar will focus on changes in the risk of California drought and pluvial due to changing oceanic conditions. Using a Bayesian analysis of the longterm instrumental precipitation record, the influence of oceanic conditions (the phases of the El NiñoSouthern Oscillation and Pacific Decadal Variability) on both drought and pluvial risk in California is found to be significant. The drought risk has increased substantially over the last half century, especially in southern California, whereas the change in the pluvial risk has been more modest. Results from idealized climate model experiments show that natural variability likely played a major role in the observed changes in risk, with global warming possibly tempering the increases. Evolving oceanic conditions during 2015 (the warm phase of Pacific Ocean) have significantly increased the likelihood of pluvial conditions over California for this winter 2015/16, suggesting the potential for drought recovery. However, the long-term outlook for a negative phase of Pacific Ocean (i.e. high transition probability from La Niña event after a strong El Niño event and a negative phase phase of Pacific Decadal Variability)