The year 2023 has been confirmed as the warmest in recorded history, with average global temperatures topping 1.5C of heating above preindustrial levels for more than one third of the year. It continues the rapid warming trend, with the 10 warmest years in human history all having occurred since 2010. So what could 2024 hold? Forecasts suggest the year ahead is likely to be another record breaker, with a strong possibility that this could be the first full year to go beyond 1.5C of warming. The ongoing El Niño event, which brings warmer waters to the tropical Pacific Ocean, is helping to push global temperatures up, but UK Met Office scientists say the main driver of the record-breaking temperatures is human-induced warming. Their global outlook for 2024 suggests we will end the year with average global temperatures somewhere between 1.34C and 1.58C above preindustrial levels. Overshooting 1.5C would be an unwelcome milestone but it would not mean we have breached the Paris agreement. Curiously, the 2015 climate accord did not define how we would recognise that the 1.5C target had been surpassed, but it is widely accepted to mean a longer-term average over 20 years or so. Rather than waiting decades for data to roll in, recent research published in Nature suggests using a blend of observations and model projections to test when 1.5C has been passed.