Australia's summers are getting longer and hotter, with extreme heat days becoming more frequent and intense. This trend is particularly evident in the country's capital cities, with Adelaide and Canberra experiencing the most significant jumps in extreme heat days. The data hides the reality of today's summers, with just 1-2C of warming across the season resulting in four times as many individual extreme heat days. The increase in extreme heat days can be seen in most capital cities, with coastal Brisbane and Sydney not showing the same strong increase due to their proximity to the ocean. The capital that gets the hottest extreme temperatures during summer is Perth, where a day over 41.3C was considered extreme before 1975, but now nearly triples in frequency. This is especially clear since the turn of the millennium, with days over 42C occurring as many times since 2000 as they did in the 90 years before that. The season's changing shape is also noticeable, with summers getting longer and starting earlier, most notably in Canberra, but also in Adelaide and Perth. This is due to the typical summertime temperatures of 1950-75 being used as a benchmark, and the monthly average temperatures first reaching that threshold and then falling back out of it. The short memory of summer is a phenomenon where people's memories are coloured by emotional experience, and they are quite good at recalibrating a new normal. This is supported by research from 2019, which found that as people were repeatedly exposed to unusual temperatures, their baseline for what was tweet-worthy shifted with it. The 'moderating' influence of the coast is another factor, with Brisbane and Sydney not seeing the same strong increase in extreme heat days due to their proximity to the ocean. Night-time temperature increases are also a significant part of summer, with hot nights providing necessary relief from daytime heat. The data shows that only Darwin and Adelaide are recording nights this hot, but they are coming around far more often today. This summer is a great example of how extremes can hide in the data, with overall Australia's summer being warm but not remarkable. However, within the season, there were several remarkable events, including major heatwaves, hospital admissions, major bushfires, and big sporting events being suspended, followed by major flooding. The first heatwave in early January was made five times more likely by human-caused climate change, and these types of events will become far more common as climate change intensifies. As summers change, so do we, with Australia now having an official heatwave warning system and policies aimed at reducing greenhouse gas emissions to net zero by 2050. However, the urgency with which to change is not quite so prominent, as people are slowly shifting their baseline and perception of what counts as remarkable types of weather. This is not just a consideration for the current generation, but for those to come, as the rate in which the climate is changing is faster than any part of our Earth system can keep up with.
