Question iii): Role of circulation and greenhouse gas increase

What role did circulation and greenhouse gas increases play in temperature extremes observed over the early 20th century, and what can we learn from the record?

At the peak of the early 20th century warming, record seasonal, monthly, and daily maximum temperatures were measured in many locations, including Eastern North America (DeGaetano and Allen, 2002) and Northern Europe in the 1930s, and Switzerland (Schaer et al., 2004) in the 1940s. Many of these records were exceeded only recently. TITAN uses a recently developed method to attribute changes in the risk of these extreme events to external influences on climate (Pall et al., 2011; Otto et al., 2012). These high-impact events currently remain unstudied but have the potential to yield considerable insights on more recentextreme events. Rigorous analysis of the observations, supported by further high-resolution modelling, evaluates and improves understanding of the causes of and contributors to extreme temperature events.