Remarks on the acceleration of global warming and the imminent breach of the 1.5{\deg}C Paris Agreement target

Abstract

To answer the questions of whether global warming is accelerating and when the 1.5{\deg}C Paris Agreement target will be exceeded, the global mean surface temperature from 1880 to 2025 is first examined using a purely graphical approach and later, in a more conventional way, using various time-domain and frequency-domain methods. In an effort to reduce variability, exogenous variables such as El Ni\~no and solar variations are taken into account. Although it ultimately remains unclear to what extent these variables are actually helpful, we feel confident in summarizing the empirical results of this study to suggest that global warming is indeed accelerating and that a breach of the 1.5{\deg}C Paris Agreement target is imminent. But when it comes to statistical significance, caution should still be exercised. While the acceleration hypothesis can be confirmed with a fair degree of certainty under reasonably plausible assumptions (albeit with the help of a bit of data snooping, which is unavoidable when building on the results of earlier studies that used virtually the same data), there is currently not enough evidence to prove that the 1.5{\deg}C target has already been exceeded. However, if 2026 and 2027 turn out to be very warm due to the approaching El Ni\~no, that could change very soon.