A year above 1.5 °C signals that Earth is most probably within the 20-year period that will reach the Paris Agreement limit

Abstract

The temperature goals of the Paris Agreement are measured as 20-year averages exceeding a pre-industrial baseline. The calendar year of 2024 was announced as the first above 1.5 °C relative to pre-industrial levels, but the implications for the corresponding temperature goal are unclear. Here we show that, without very stringent climate mitigation, the first year above 1.5 °C occurs within the first 20-year period with an average warming of 1.5 °C. What a first year with temperature 1.5 °C above the pre-industrial baseline implies for long-term temperature goals is unclear. Here the authors show that such a first year above the baseline is highly likely to occur within the first 20-year period with average warming of 1.5 °C.