More Like this

1. Highly restricted near‐surface permafrost extent during the mid-Pliocene warm period

   https://doi.org/10.1073/pnas.2301954120  

   Guo, Donglin; Wang, Huijun; Romanovsky, Vladimir E.; Haywood, Alan M.; Pepin, Nick; Salzmann, Ulrich; Sun, Jianqi; Yan, Qing; Zhang, Zhongshi; Li, Xiangyu; et al (September 2023, Proceedings of the National Academy of Sciences)

   Accurate understanding of permafrost dynamics is critical for evaluating and mitigating impacts that may arise as permafrost degrades in the future; however, existing projections have large uncertainties. Studies of how permafrost responded historically during Earth’s past warm periods are helpful in exploring potential future permafrost behavior and to evaluate the uncertainty of future permafrost change projections. Here, we combine a surface frost index model with outputs from the second phase of the Pliocene Model Intercomparison Project to simulate the near‐surface (~3 to 4 m depth) permafrost state in the Northern Hemisphere during the mid-Pliocene warm period (mPWP, ~3.264 to 3.025 Ma). This period shares similarities with the projected future climate. Constrained by proxy-based surface air temperature records, our simulations demonstrate that near‐surface permafrost was highly spatially restricted during the mPWP and was 93 ± 3% smaller than the preindustrial extent. Near‐surface permafrost was present only in the eastern Siberian uplands, Canadian high Arctic Archipelago, and northernmost Greenland. The simulations are similar to near‐surface permafrost changes projected for the end of this century under the SSP5-8.5 scenario and provide a perspective on the potential permafrost behavior that may be expected in a warmer world. 

   more » « less
2. Pacific warm pool subsurface heat sequestration modulated Walker circulation and ENSO activity during the Holocene

   https://doi.org/10.1126/sciadv.abc0402  

   Dang, Haowen; Jian, Zhimin; Wang, Yue; Mohtadi, Mahyar; Rosenthal, Yair; Ye, Liming; Bassinot, Franck; Kuhnt, Wolfgang (October 2020, Science Advances)

   Dynamics driving the El Niño–Southern Oscillation (ENSO) over longer-than-interannual time scales are poorly understood. Here, we compile thermocline temperature records of the Indo-Pacific warm pool over the past 25,000 years, which reveal a major warming in the Early Holocene and a secondary warming in the Middle Holocene. We suggest that the first thermocline warming corresponds to heat transport of southern Pacific shallow overturning circulation driven by June (austral winter) insolation maximum. The second thermocline warming follows equatorial September insolation maximum, which may have caused a steeper west-east upper-ocean thermal gradient and an intensified Walker circulation in the equatorial Pacific. We propose that the warm pool thermocline warming ultimately reduced the interannual ENSO activity in the Early to Middle Holocene. Thus, a substantially increased oceanic heat content of the warm pool, acting as a negative feedback for ENSO in the past, may play its role in the ongoing global warming. 

   more » « less
3. Pliocene Warmth and Patterns of Climate Change Inferred From Paleoclimate Data Assimilation

   https://doi.org/10.1029/2024AV001356  

   Tierney, Jessica E; King, Jonathan; Osman, Matthew B; Abell, Jordan T; Burls, Natalie J; Erfani, Ehsan; Cooper, Vincent T; Feng, Ran (February 2025, AGU Advances)

   Abstract As the last time period when concentrations were near 400 ppm, the Pliocene Epoch (5.33–2.58 Ma) is a useful paleoclimate target for understanding future climate change. Existing estimates of global warming and climate sensitivity during the Pliocene rely mainly on model simulations. To reconstruct Pliocene climate and incorporate paleoclimate observations, we use data assimilation to blend sea‐surface temperature (SST) proxies with model simulations from the Pliocene Modeling Intercomparison Project 2 and the Community Earth System Models. The resulting reconstruction, “plioDA,” suggests that the mid‐Pliocene (3.25 Ma) was warmer than previously thought (on average 4.1°C warmer than preindustrial, 95% CI = 3.0°C–5.3°C), leading to a higher estimate of climate sensitivity (4.8°C per doubling of , 90% CI = 2.6°C–9.9°C). In agreement with previous work, the tropical Pacific zonal SST gradient during the mid‐Pliocene was moderately reduced (°C, 95% CI = –0.4°C). However, this gradient was more reduced during the early Pliocene (4.75 Ma, -2.3°C, 95% CI = -3.9t to -1.1°C), a time period that is also warmer than the mid‐Pliocene (4.8°C above preindustrial, 95% CI = 3.6°C–6.2°C). PlioDA reconstructs a fresh North Pacific and salty North Atlantic, supporting Arctic gateway closure and contradicting the presence of Pacific Deep Water formation. Overall, plioDA updates our view of global and spatial climate change during the Pliocene, as well as raising questions about the state of ocean circulation and the drivers of differences between the early and mid‐Pliocene. 

   more » « less
4. Aerosol uncertainties in tropical precipitation changes for the mid-Pliocene warm period

   https://doi.org/10.5194/cp-20-1195-2024  

   Zhao, Anni; Feng, Ran; Brierley, Chris M; Zhang, Jian; Hu, Yongyun (January 2024, Climate of the Past)

   Abstract. The mid-Pliocene Warm Period (mPWP, 3.3–3.0 Ma) was characterised by an atmospheric CO2 concentration exceeding 400 ppmv with minor changes in continental and orbital configurations. Simulations of this past climate state have improved with newer models but still show some substantial differences from proxy reconstructions. There is little information about atmospheric aerosol concentrations during the Pliocene, but previous work suggests that it could have been quite different from the modern period. Here we apply idealised aerosol scenario experiments to examine the importance of aerosol forcing on mPWP tropical precipitation and the possibility of aerosol uncertainty explaining the mismatch between reconstructions and simulations. The absence of industrial pollutants leads to further warming, especially in the Northern Hemisphere. The Intertropical Convergence Zone (ITCZ) becomes narrower and stronger and shifts northward after removal of anthropogenic aerosols. Though not affecting the location of monsoon domain boundary, removal of anthropogenic aerosol alters the amount of rainfall within the domain, increasing summer rain rate over eastern and southern Asia and western Africa. This work demonstrates that uncertainty in aerosol forcing could be the dominant driver in tropical precipitation changes during the mid-Pliocene: causing larger impacts than the changes in topography and greenhouse gases. 

   more » « less
5. Geologically constrained 2-million-year-long simulations of Antarctic Ice Sheet retreat and expansion through the Pliocene

   https://doi.org/10.1038/s41467-024-51205-z  

   Halberstadt, Anna_Ruth W; Gasson, Edward; Pollard, David; Marschalek, James; DeConto, Robert M (December 2024, Nature Communications)

   Abstract Pliocene global temperatures periodically exceeded modern levels, offering insights into ice sheet sensitivity to warm climates. Ice-proximal geologic records from this period provide crucial but limited glimpses of Antarctic Ice Sheet behavior. We use an ice sheet model driven by climate model snapshots to simulate transient glacial cyclicity from 4.5 to 2.6 Ma, providing spatial and temporal context for geologic records. By evaluating model simulations against a comprehensive synthesis of geologic data, we translate the intermittent geologic record into a continuous reconstruction of Antarctic sea level contributions, revealing a dynamic ice sheet that contributed up to 25 m of glacial-interglacial sea level change. Model grounding line behavior across all major Antarctic catchments exhibits an extended period of receded ice during the mid-Pliocene, coincident with proximal geologic data around Antarctica but earlier than peak warmth in the Northern Hemisphere. Marine ice sheet collapse is triggered with 1.5 °C model subsurface ocean warming. 

   more » « less