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1. The Peculiar Trajectory of Global Warming

   https://doi.org/10.1029/2020JD033629  

   Fueglistaler, S. ; Silvers, L. G. ( February 2021 , Journal of Geophysical Research: Atmospheres)

   General Circulation Model (GCM) simulations with prescribed observed sea surface temperature (SST) over the historical period show systematic global shortwave cloud radiative effect (SWCRE) variations uncorrelated with global surface temperature (known as “pattern effect”). Here, we show that a single parameter that quantifies the difference in SSTs between regions of tropical deep convection and the tropical or global average (Δ^conv) captures the time‐varying “pattern effect” in the simulations using the PCMDI/AMIPII SST recommended for CMIP6. In particular, a large positive trend in the 1980s–1990s in Δ^convexplains the change of sign to a strongly negative SWCRE feedback since the late 1970s. In these decades, the regions of deep convection warm about +50% more than the tropical average. Such an amplification is rarely observed in forced coupled atmosphere‐ocean GCM simulations, where the amplified warming is typically about +10%. During the post 2000 global warming hiatus Δ^convshows little change, and the more recent period of resumed global warming is too short to robustly detect trends. In the prescribed SST simulations, Δ^convis forced by the SST difference between warmer and colder regions. An index thereof (SST^#) evaluated for six SST reconstructions shows similar trends for the satellite era, but the difference between the pre‐ and the satellite era is substantially larger in the PCMDI/AMIPII SSTs than in the other reconstructions. Quantification of the cloud feedback depends critically on small changes in the shape of the SST probability density distribution. These sensitivities underscore how essential highly accurate, persistent, and stable global climate records are to determine the cloud feedback.

    

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2. Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution

   https://doi.org/10.1038/s41467-020-20187-z  

   Wang, Karen Jiaxi ; Huang, Yongsong ; Majaneva, Markus ; Belt, Simon T. ; Liao, Sian ; Novak, Joseph ; Kartzinel, Tyler R. ; Herbert, Timothy D. ; Richter, Nora ; Cabedo-Sanz, Patricia ( January 2021 , Nature Communications)

   Alkenones are biomarkers produced solely by algae in the order Isochrysidales that have been used to reconstruct sea surface temperature (SST) since the 1980s. However, alkenone-based SST reconstructions in the northern high latitude oceans show significant bias towards warmer temperatures in core-tops, diverge from other SST proxies in down core records, and are often accompanied by anomalously high relative abundance of the C₃₇tetra-unsaturated methyl alkenone (%C_37:4). Elevated %C_37:4is widely interpreted as an indicator of low sea surface salinity from polar water masses, but its biological source has thus far remained elusive. Here we identify a lineage of Isochrysidales that is responsible for elevated C_37:4methyl alkenone in the northern high latitude oceans through next-generation sequencing and lab-culture experiments. This Isochrysidales lineage co-occurs widely with sea ice in marine environments and is distinct from other known marine alkenone-producers, namelyEmiliania huxleyiandGephyrocapsa oceanica. More importantly, the %C_37:4in seawater filtered particulate organic matter and surface sediments is significantly correlated with annual mean sea ice concentrations. In sediment cores from the Svalbard region, the %C_37:4concentration aligns with the Greenland temperature record and other qualitative regional sea ice records spanning the past 14 kyrs, reflecting sea ice concentrations quantitatively. Our findings imply that %C_37:4is a powerful proxy for reconstructing sea ice conditions in the high latitude oceans on thousand- and, potentially, on million-year timescales.

    

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3. An Integrated View of Organic Biomarker‐Based Sea Surface Temperature Changes in the Subarctic Pacific Since the Last Ice Age

   https://doi.org/10.1029/2022PA004480  

   Li, Qian ; Chen, Min‐Te ; Li, Guangxue ; Yu, Jimin ; Zou, Jianjun ; Shi, Xuefa ; Liu, Shidong ; Yu, Pai‐Sen ( December 2022 , Paleoceanography and Paleoclimatology)

   The phase relationships of sea surface temperature (SST) changes between the North Pacific and North Atlantic during deglacial millennial‐scale climate events have been of great interest. However, uncertainties remain partly due to the sparsity of deglacial SST records in the North Pacific. This study presents a new high‐resolution‐SST record spanning the entire last deglaciation from core LV63‐41‐2 retrieved from the Northwestern Pacific off the Kamchatka Peninsula, which allows us to explore regional SST change patterns and associated driving mechanisms by compiling previously published SST data in the subarctic Pacific. The subarctic Pacific SST changes during the Bølling‐Allerød and Younger Dryas show in‐phase relationships in response to the North Atlantic SST variations, suggesting a dominant control of atmospheric teleconnections between both oceans. During Heinrich Stadial 1 (HS1) when the North Atlantic exhibited significant cooling, the subarctic Pacific SST developments are complex, showing gradual warming from the Last Glacial Maximum to HS1 in the Northwestern Pacific and cooling at the onset of HS1 in the Northeastern Pacific. We suggest that the inconsistent phase responses resulted from the combined effects of multiple processes, which involve an enhanced poleward advection of warm subtropical waters, cold meltwater inputs from the retreating Cordilleran Ice Sheet into the Northeastern Pacific, and a persistent La Niña‐like state in the tropical Pacific.

    

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4. The Pacific Northwest Heat Wave of 25–30 June 2021: Synoptic/Mesoscale Conditions and Climate Perspective

   https://doi.org/10.1175/WAF-D-23-0154.1  

   Mass, Clifford ; Ovens, David ; Christy, John ; Conrick, Robert ( February 2024 , Weather and Forecasting)

   An unprecedented heat wave occurred over the Pacific Northwest and southwest Canada on 25–30 June 2021, resulting in all-time temperature records that greatly exceeded previous record maximum temperatures. The impacts were substantial, including several hundred deaths, thousands of hospitalizations, a major wildfire in Lytton, British Columbia, Canada, and severe damage to regional vegetation. Several factors came together to produce this extreme event: a record-breaking midtropospheric ridge over British Columbia in the optimal location, record-breaking midtropospheric temperatures, strong subsidence in the lower atmosphere, low-level easterly flow that produced downslope warming on regional terrain and the removal of cooler marine air, an approaching low-level trough that enhanced downslope flow, the occurrence at a time of maximum insolation, and drier-than-normal soil moisture. It is shown that all-time-record temperatures have not become more frequent and that annual high temperatures only increased at the rate of baseline global warming. Although anthropogenic warming may have contributed as much as 1°C to the event, there is little evidence of further amplification from increasing greenhouse gases. Weather forecasts were excellent for this event, with highly accurate predictions of the extreme temperatures.

   This paper describes the atmospheric evolution that produced an extreme heat wave over the Pacific Northwest during June 2021 and puts this event into historical perspective.

    

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5. On the Effect of Historical SST Patterns on Radiative Feedback

   https://doi.org/10.1029/2022JD036675  

   Andrews, Timothy ; Bodas‐Salcedo, Alejandro ; Gregory, Jonathan M. ; Dong, Yue ; Armour, Kyle C. ; Paynter, David ; Lin, Pu ; Modak, Angshuman ; Mauritsen, Thorsten ; Cole, Jason N. S. ; et al ( September 2022 , Journal of Geophysical Research: Atmospheres)

   We investigate the dependence of radiative feedback on the pattern of sea‐surface temperature (SST) change in 14 Atmospheric General Circulation Models (AGCMs) forced with observed variations in SST and sea‐ice over the historical record from 1871 to near‐present. We find that over 1871–1980, the Earth warmed with feedbacks largely consistent and strongly correlated with long‐term climate sensitivity feedbacks (diagnosed from corresponding atmosphere‐ocean GCMabrupt‐4xCO2simulations). Post 1980, however, the Earth warmed with unusual trends in tropical Pacific SSTs (enhanced warming in the west, cooling in the east) and cooling in the Southern Ocean that drove climate feedback to be uncorrelated with—and indicating much lower climate sensitivity than—that expected for long‐term CO₂increase. We show that these conclusions are not strongly dependent on the Atmospheric Model Intercomparison Project (AMIP) II SST data set used to force the AGCMs, though the magnitude of feedback post 1980 is generally smaller in nine AGCMs forced with alternative HadISST1 SST boundary conditions. We quantify a “pattern effect” (defined as the difference between historical and long‐term CO₂feedback) equal to 0.48 ± 0.47 [5%–95%] W m⁻² K⁻¹for the time‐period 1871–2010 when the AGCMs are forced with HadISST1 SSTs, or 0.70 ± 0.47 [5%–95%] W m⁻² K⁻¹when forced with AMIP II SSTs. Assessed changes in the Earth's historical energy budget agree with the AGCM feedback estimates. Furthermore satellite observations of changes in top‐of‐atmosphere radiative fluxes since 1985 suggest that the pattern effect was particularly strong over recent decades but may be waning post 2014.

    

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