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- ItemInvestigating Mesozoic Climate Trends and Sensitivities With a Large Ensemble of Climate Model Simulations(Hoboken, NJ : Wiley, 2021) Landwehrs, Jan; Feulner, Georg; Petri, Stefan; Sames, Benjamin; Wagreich, MichaelThe Mesozoic era (∼252 to 66 million years ago) was a key interval in Earth's evolution toward its modern state, witnessing the breakup of the supercontinent Pangaea and significant biotic innovations like the early evolution of mammals. Plate tectonic dynamics drove a fundamental climatic transition from the early Mesozoic supercontinent toward the Late Cretaceous fragmented continental configuration. Here, key aspects of Mesozoic long-term environmental changes are assessed in a climate model ensemble framework. We analyze so far the most extended ensemble of equilibrium climate states simulated for evolving Mesozoic boundary conditions covering the period from 255 to 60 Ma in 5 Myr timesteps. Global mean temperatures are generally found to be elevated above the present and exhibit a baseline warming trend driven by rising sea levels and increasing solar luminosity. Warm (Triassic and mid-Cretaceous) and cool (Jurassic and end-Cretaceous) anomalies result from pCO2 changes indicated by different reconstructions. Seasonal and zonal temperature contrasts as well as continental aridity show an overall decrease from the Late Triassic-Early Jurassic to the Late Cretaceous. Meridional temperature gradients are reduced at higher global temperatures and less land area in the high latitudes. With systematic sensitivity experiments, the influence of paleogeography, sea level, vegetation patterns, pCO2, solar luminosity, and orbital configuration on these trends is investigated. For example, long-term seasonality trends are driven by paleogeography, but orbital cycles could have had similar-scale effects on shorter timescales. Global mean temperatures, continental humidity, and meridional temperature gradients are, however, also strongly affected by pCO2.
- ItemA Pronounced Spike in Ocean Productivity Triggered by the Chicxulub Impact(Hoboken, NJ : Wiley, 2021) Brugger, Julia; Feulner, Georg; Hofmann, Matthias; Petri, StefanThere is increasing evidence linking the mass-extinction event at the Cretaceous-Paleogene boundary to an asteroid impact near Chicxulub, Mexico. Here we use model simulations to explore the combined effect of sulfate aerosols, carbon dioxide and dust from the impact on the oceans and the marine biosphere in the immediate aftermath of the impact. We find a strong temperature decrease, a brief algal bloom caused by nutrients from both the deep ocean and the projectile, and moderate surface ocean acidification. Comparing the modeled longer-term post-impact warming and changes in carbon isotopes with empirical evidence points to a substantial release of carbon from the terrestrial biosphere. Overall, our results shed light on the decades to centuries after the Chicxulub impact which are difficult to resolve with proxy data.
- ItemFuture Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets(Hoboken, NJ : Wiley, 2021) Payne, Antony J.; Nowicki, Sophie; Abe‐Ouchi, Ayako; Agosta, Cécile; Alexander, Patrick; Albrecht, Torsten; Asay‐Davis, Xylar; Aschwanden, Andy; Barthel, Alice; Bracegirdle, Thomas J.; Calov, Reinhard; Chambers, Christopher; Choi, Youngmin; Cullather, Richard; Cuzzone, Joshua; Dumas, Christophe; Edwards, Tamsin L.; Felikson, Denis; Fettweis, Xavier; Galton‐Fenzi, Benjamin K.; Goelzer, Heiko; Gladstone, Rupert; Golledge, Nicholas R.; Gregory, Jonathan M.; Greve, Ralf; Hattermann, Tore; Hoffman, Matthew J.; Humbert, Angelika; Huybrechts, Philippe; Jourdain, Nicolas C.; Kleiner, Thomas; Munneke, Peter Kuipers; Larour, Eric; Le clec'h, Sebastien; Lee, Victoria; Leguy, Gunter; Lipscomb, William H.; Little, Christopher M.; Lowry, Daniel P.; Morlighem, Mathieu; Nias, Isabel; Pattyn, Frank; Pelle, Tyler; Price, Stephen F.; Quiquet, Aurélien; Reese, Ronja; Rückamp, Martin; Schlegel, Nicole‐Jeanne; Seroussi, Hélène; Shepherd, Andrew; Simon, Erika; Slater, Donald; Smith, Robin S.; Straneo, Fiammetta; Sun, Sainan; Tarasov, Lev; Trusel, Luke D.; Van Breedam, Jonas; Wal, Roderik; Broeke, Michiel; Winkelmann, Ricarda; Zhao, Chen; Zhang, Tong; Zwinger, ThomasProjections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming.
- ItemDeadly Heat Stress to Become Commonplace Across South Asia Already at 1.5°C of Global Warming(Hoboken, NJ : Wiley, 2021) Saeed, Fahad; Schleussner, Carl‐Friedrich; Ashfaq, MoetasimSouth Asia (SA) is one of those hotspots where earliest exposure to deadly wet-bulb temperatures (Tw >35°C) is projected in warmer future climates. Here we find that even today parts of SA experience the upper limits of labor productivity (Tw >32°C) or human survivability (Tw >35°C), indicating that previous estimates for future exposure to Tw-based extremes may be conservative. Our results show that at 2°C global warming above pre-industrial levels, the per person exposure approximately increases by 2.2 (2.7) folds for unsafe labor (lethal) threshold compared to the 2006–2015 reference period. Limiting warming to 1.5°C would avoid about half that impact. The population growth under the middle-of-the-road socioeconomic pathway could further increase these exposures by a factor of ∼2 by the mid-century. These results indicate an imminent need for adaptation measures, while highlighting the importance of stringent Paris-compatible mitigation actions for limiting future emergence of such conditions in SA.
- ItemEarly Warning of the Pacific Decadal Oscillation Phase Transition Using Complex Network Analysis(Hoboken, NJ : Wiley, 2021) Lu, Zhenghui; Yuan, Naiming; Yang, Qing; Ma, Zhuguo; Kurths, JürgenObtaining an efficient prediction of the Pacific Decadal Oscillation (PDO) phase transition is a worldwide challenge. Here, we employed the climate network analysis to uncover early warning signals prior to a PDO phase transition. This way an examination of cooperative behavior in the PDO region revealed an enhanced signal that propagated from the western Pacific to the northwest coast of North America. The detection of this signal corresponds very well to the time when the upper ocean heat content in the off-equatorial northwestern tropical Pacific reaches a threshold, in which case a PDO phase transition may be expected with the arising of the next El Ni urn:x-wiley:00948276:media:grl61986:grl61986-math-0001o/La Niurn:x-wiley:00948276:media:grl61986:grl61986-math-0002 a event. The objectively detected early warning signal successfully forewarned all the six PDO phase transitions from the 1890–2000, and also underpinned the possible PDO phase transition around 2015, which may be triggered by the strong El Niurn:x-wiley:00948276:media:grl61986:grl61986-math-0003o event in 2015–2016.