**THIS TALK IS CANCELLED**

It sounds straightforward. As the Earth warms due to the increased concentration of greenhouse gases in the atmosphere, global temperatures rise and so heatwaves become warmer as well. Another way to describe this is that a fixed temperature threshold is passed more often: the probability of extreme heat increases. Climate models also simulate heatwaves and should be able to simulate the increased intensity and probability of extreme heat to aid planning for adaptation for these, often deadly, events and to raise awareness of the need to curb greenhouse gas emissions. We’ll discuss the reasons why, in practice, the trends in hot days in observations and models often disagree,  and why attribution and projection of heat waves remains a major scientific challenge.