Fiches info

There is increasing concern that the Atlantic Meridional Overturning Circulation (AMOC) may collapse this century with a disrupting societal impact on large parts of the world. Preliminary estimates of the probability of such an AMOC collapse have so far been based on conceptual models and statistical analyses of proxy data. Here, we provide observationally based estimates of such probabilities from reanalysis data. We first identify optimal observation regions of an AMOC collapse from a recent global climate model simulation. Salinity data near the southern boundary of the Atlantic turn out to be optimal to provide estimates of the time of the AMOC collapse in this model. Based on the reanalysis products, we next determine probability density functions of the AMOC collapse time. The collapse time is estimated between 2037-2064 (10-90% CI) with a mean of 2050 and the probability of an AMOC collapse before the year 2050 is estimated to be 59±17%.

The Atlantic Meridional Overturning Circulation (AMOC), a major ocean current system transporting warm surface waters toward the northern Atlantic, has been suggested to exhibit two distinct modes of operation. A collapse from the currently attained strong to the weak mode would have severe impacts on the global climate system and further multi-stable Earth system components. Observations and recently suggested fingerprints of AMOC variability indicate a gradual weakening during the last decades, but estimates of the critical transition point remain uncertain.

Bruits de bottes aux frontières russo-ukrainiennes en avril1, appel à la désescalade et à l’arrêt des provocations russes sur ses marches traditionnelles, perception de la menace systémique chinoise2, confrontation sino-indienne dans l’Himalaya, mise en évidence de la faiblesse européenne face aux rodomontades d’États nationalistes et autoritaires, enjeux militaires autour du « déni d’accès » russe, implication du GRU (direction générale des renseignements militaires russes) dans l’explosion d’entrepôts d’armes en Tchéquie et destinées à l’Ukraine en 2014, usage de l’hybridation alliant stratégies indirectes et usage militaire classique, insistance occidentale sur le rôle stratégique des forces terrestres3 : tout concourt à suggérer un retour des engagements militaires, sinon du spectre de la haute intensité et ... de l’ascension aux extrêmes. L’annexion de la Crimée est passée par là, tout comme la « question chinoise ».