This workpackage analyzes the observed temperature and precipitation records using circulation states and clearly defined modes of variability (see Kenyon and Hegerl, 2008). It also employs methods that separate the contributions by external forcing from those due to climate dynamics based on observations only (e.g., Wallace et al., 1997; Hegerl and Wallace, 2002). The state of the atmospheric circulation is determined using the 20th century reanalysis (Compo et al., 2011). An analysis using model fingerprints identifies if forcing has caused detectable changes in circulation. The project analyzes the circulation states, in observations, that explain key warm and cold temperature extremes of the early Anthropocene, including, but not limited to, the early 20th century. An analogue method (Cattiaux et al., 2010) is applied for the first time to mid- 20th century extremes, addressing the question: How extreme would these extremes events be, given the observed circulation state, if occurring today?

This WP will contribute to question i), ii), and iii) and links closely to WP3.