Varying planetary heat sink led to global-warming slowdown and acceleration


    • Le résumé de l’article de Science

      Varying planetary heat sink led to global-warming slowdown and acceleration

      A vacillating global heat sink at intermediate ocean depths is associated with different climate regimes of surface warming under anthropogenic forcing: The latter part of the 20th century saw rapid global warming as more heat stayed near the surface. In the 21st century, surface warming slowed as more heat moved into deeper oceans. In situ and reanalyzed data are used to trace the pathways of ocean heat uptake. In addition to the shallow La Niña–like patterns in the Pacific that were the previous focus, we found that the slowdown is mainly caused by heat transported to deeper layers in the Atlantic and the Southern oceans, initiated by a recurrent salinity anomaly in the subpolar North Atlantic. Cooling periods associated with the latter deeper heat-sequestration mechanism historically lasted 20 to 35 years.

      Une visualisation du stockage d’énergie

      illustrant cette courte présentation

      Earth’s missing heat may be hiding in the deep Atlantic | Science/AAAS | News

      The work draws on tens of millions of ocean temperature and salinity measurements taken globally by buoys, floats, and ships since 1970. Covering 24 depths from the sea surface down to 1500 meters, the data suggest that over the last decade or so the Atlantic has been absorbing heat (red in the graphic above) that would have otherwise warmed the surface. Over the past 14 years, the authors write, water below 300 meters in the North and South Atlantic oceans has stored more energy than the rest of the global oceans combined.

      L’édito de Science sur le sujet qui remet en contexte, présente les autres hypothèses sur le rôle de la circulation océanique et rappelle qu’il ne s’agit que d’une pause apparente, puisque l’accumulation de chaleur se poursuit, mais hors de notre vue.

      Pas sûr que cela suffise à neutraliser les climato-sceptiques…

      Is Atlantic holding Earth’s missing heat ?

      Armchair detectives might call it the case of Earth’s missing heat: Why have average global surface air temperatures remained essentially steady since 2000, even as greenhouse gases have continued to accumulate in the atmosphere? The suspects include changes in atmospheric water vapor, a strong greenhouse gas, or the noxious sunshade of haze emanating from factories. Others believe the culprit is the mighty Pacific Ocean, which has been sending vast slugs of cold bottom water to the surface. But two fresh investigations finger a new suspect: the Atlantic Ocean. One study, in this issue of Science, presents sea temperature data implying that most of the missing heat has been stored deep in the Atlantic. The other, published online in Nature Climate Change, suggests a warming Atlantic is abetting the Pacific by driving wind patterns that help that ocean cool the atmosphere. But some climate specialists remain skeptical. In a third recent paper, also published online in Nature Climate Change, other researchers argue that the Pacific remains the kingpin. One reason some scientists remain convinced the Pacific is behind the hiatus is a measured speedup in trade winds that drive a massive upwelling of cold water in the eastern Pacific. But there, too, the Atlantic may be responsible, modeling experiments suggest. A consensus about what has put global warming on pause may be years away, but one scientist says the recent papers confirm that Earth’s warming has continued during the hiatus, at least in the ocean depths, if not in the air.