Heatwaves of this scale, the report forecasts, are expected to occur just once every 500 years. Such rare occurrences make it challenging for researchers to estimate how often these events might happen if the climate warms further. But the current attribution study estimates that, if the climate warms another 1.3°C, heat events so extreme that they are forecasted to happen just once every 100 years will become 6.4 times more likely and 1.8°C hotter.