scholarly journals Scant evidence for a volcanically forced winter warming over Eurasia following the Krakatau eruption of August 1883

2020 ◽  
Vol 20 (22) ◽  
pp. 13687-13700
Author(s):  
Lorenzo M. Polvani ◽  
Suzana J. Camargo
Keyword(s):  
Coupled Model ◽  
Large Magnitude ◽  
Low Latitude ◽  
Surface Warming ◽  
Winter Warming ◽  
Pinatubo Eruption ◽  
Intercomparison Project ◽  
Volcanic Aerosols ◽  
Instrumental Period ◽  
New Evidence

Abstract. A recent study has presented compelling new evidence suggesting that the observed Eurasian warming in the winter following the 1992 Pinatubo eruption was, in all likelihood, unrelated to the presence of volcanic aerosols in the stratosphere. Building on that study, we turn our attention to the only other low-latitude eruption in the instrumental period with a comparably large magnitude: the Krakatau eruption of August 1883. We study the temperature anomalies in the first winter following that eruption in detail, analyzing (1) observations, (2) reanalyses, and (3) models. Three findings emerge from our analysis. First, the observed post-Krakatau winter warming over Eurasia was unremarkable (only between 1σ and 2σ of the distribution from 1850 to present). Second, reanalyses based on assimilating surface pressure alone indicate the existence of very large uncertainties, so much so that a Eurasian cooling is not incompatible with those reanalyses. Third, models robustly show the complete absence of a volcanically forced Eurasian winter warming: here, we analyze both a 100-member initial-condition ensemble and 140 simulations from Phase 5 of the Coupled Model Intercomparison Project. This wealth of evidence strongly suggests that, as in the case of Pinatubo, the observed warming over Eurasia in the winter of 1883–84 was, in all likelihood, unrelated to the Krakatau eruption. This, taken together with a similar result for Pinatubo, leads us to conclude that if volcanically forced Eurasian winter warming exists at all, an eruption with a magnitude far exceeding these two events would be needed to produce a detectable surface warming.

scholarly journals Scant evidence for a volcanically forced winter warming over Eurasia following the Krakatau eruption of August 1883

2020 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Suzana J. Camargo
Keyword(s):  
Coupled Model ◽  
Initial Condition ◽  
Model Intercomparison ◽  
Low Latitude ◽  
Winter Warming ◽  
Pinatubo Eruption ◽  
Intercomparison Project ◽  
Volcanic Aerosols ◽  
Instrumental Period ◽  
New Evidence

Abstract. A recent study has presented compelling new evidence suggesting that the observed Eurasian warming in the winter following the 1992 Pinatubo eruption was, in all likelihood, unrelated to the presence of volcanic aerosols in the stratosphere. Building on that study, we here turn our attention to the only other low-latitude eruption in the instrumental period with a comparably large Volcanic Explosivity Index (VEI): the Krakatau eruption of August 1883. We study in detail the temperature anomalies in the first winter following that eruption, analyzing (1) observations, (2) reanalyses, and (3) models. Three findings emerge from our analysis. First, the observed post-Krakatau winter warming over Eurasia was unremarkable (only between 1- and 2-σ of the distribution from 1850 to present). Second, reanalyses indicate the existence of very large uncertainties, so much so that a Eurasian cooling is not incompatible with observations. Third, models robustly show the complete absence of a volcanically forced Eurasian winter warming: we here analyze both a 100-member initial-condition ensemble, and 140 simulations from the Phase 5 of Coupled Model Intercomparison Project. This wealth of evidence strongly suggests that, as in the case of Pinatubo, the observed warming over Eurasia in the winter of 1883/84 was, in all likelihood, unrelated to the Krakatau eruption. Together with the results for Pinatubo, we are led to conclude that if volcanically forced Eurasian winter warming exists at all, an eruption with a magnitude far exceeding these two (VEI = 6) events is needed.

scholarly journals Forced and Unforced Decadal Behavior of the Interhemispheric SST Contrast during the Instrumental Period (1881–2012): Contextualizing the Late 1960s–Early 1970s Shift

2020 ◽  
Vol 33 (9) ◽  
pp. 3487-3509 ◽  
Author(s):  
Andrew R. Friedman ◽  
Gabriele C. Hegerl ◽  
Andrew P. Schurer ◽  
Shih-Yu Lee ◽  
Wenwen Kong ◽  
...  
Keyword(s):  
Coupled Model ◽  
Internal Variability ◽  
Forced Response ◽  
Meridional Overturning Circulation ◽  
Large Magnitude ◽  
Sst Cooling ◽  
Sst Variability ◽  
External Forcings ◽  
Sst Warming ◽  
Instrumental Period

AbstractThe sea surface temperature (SST) contrast between the Northern Hemisphere (NH) and Southern Hemisphere (SH) influences the location of the intertropical convergence zone (ITCZ) and the intensity of the monsoon systems. This study examines the contributions of external forcing and unforced internal variability to the interhemispheric SST contrast in HadSST3 and ERSSTv5 observations, and 10 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) from 1881 to 2012. Using multimodel mean fingerprints, a significant influence of anthropogenic, but not natural, forcing is detected in the interhemispheric SST contrast, with the observed response larger than that of the model mean in ERSSTv5. The forced response consists of asymmetric NH–SH SST cooling from the mid-twentieth century to around 1980, followed by opposite NH–SH SST warming. The remaining best-estimate residual or unforced component is marked by NH–SH SST maxima in the 1930s and mid-1960s, and a rapid NH–SH SST decrease around 1970. Examination of decadal shifts in the observed interhemispheric SST contrast highlights the shift around 1970 as the most prominent from 1881 to 2012. Both NH and SH SST variability contributed to the shift, which appears not to be attributable to external forcings. Most models examined fail to capture such large-magnitude shifts in their control simulations, although some models with high interhemispheric SST variability are able to produce them. Large-magnitude shifts produced by the control simulations feature disparate spatial SST patterns, some of which are consistent with changes typically associated with the Atlantic meridional overturning circulation (AMOC).

Role of cloud feedback in continental warming response to CO2 physiological forcing

2021 ◽  
pp. 1-49
Author(s):  
So-Won Park ◽  
Jong-Seong Kug ◽  
Sang-Yoon Jun ◽  
Su-Jong Jeong ◽  
Jin-Soo Kim
Keyword(s):  
Land Surface ◽  
Atmospheric Carbon Dioxide ◽  
Stomatal Closure ◽  
Coupled Model ◽  
Cloud Feedback ◽  
Climate Feedback ◽  
Primary Role ◽  
Surface Warming ◽  
Surface Energy Fluxes ◽  
Intercomparison Project

AbstractStomatal closure is a major physiological response to the increasing atmospheric carbon dioxide (CO2), which can lead to surface warming by regulating surface energy fluxes—a phenomenon known as CO2 physiological forcing. The magnitude of land surface warming caused by physiological forcing is substantial and varies across models. Here we assess the continental warming response to CO2 physiological forcing and quantify the resultant climate feedback using carbon–climate simulations from phases 5 and 6 of the Coupled Model Intercomparison Project, with a focus on identifying the cause of inter-model spread. It is demonstrated that the continental (40°–70°N) warming response to the physiological forcing in summer (~0.55 K) is amplified primarily due to cloud feedback (~1.05 K), whereas the other climate feedbacks, ranged from –0.57 K to 0.20 K, show relatively minor contributions. In addition, the strength of cloud feedback varies considerably across models, which plays a primary role in leading large diversity of the continental warming response to the physiological forcing.

scholarly journals Northern Hemisphere continental winter warming following the 1991 Mt. Pinatubo eruption: reconciling models and observations

2019 ◽  
Vol 19 (9) ◽  
pp. 6351-6366 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Antara Banerjee ◽  
Anja Schmidt
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Climate Model ◽  
State Of The Art ◽  
Polar Vortex ◽  
Internal Variability ◽  
Simple Fact ◽  
Surface Warming ◽  
Winter Warming ◽  
Pinatubo Eruption

Abstract. It has been suggested, and is widely believed, that the anomalous surface warming observed over the Northern Hemisphere continents in the winter following the 1991 eruption of Mt. Pinatubo was, in fact, caused by that eruption, via a stratospheric pathway that involves a strengthening of the polar vortex. However, most studies that have examined multiple, state-of-the-art, coupled climate models report that, in the ensemble mean, the models do not show winter warming after the Mt. Pinatubo eruption. This lack of surface warming in the multi-model mean, concomitant with a frequent lack of strengthening of the polar vortex, is often interpreted as a failure of the models to reproduce the observations. In this paper we show that this interpretation is erroneous, as averaging many simulations from different models, or from the same model, is not expected to yield surface anomalies similar to the observed ones, even if the models were highly accurate, owing to the presence of strong internal variability. We here analyze three large ensembles of state-of-the-art, coupled climate model simulations and show that, in all three, many individual ensemble members are able to produce post-Pinatubo surface warming in winter that is comparable to the observed one. This establishes that current-generation climate models are perfectly capable of reproducing the observed surface post-eruption warming. We also confirm the bulk of previous studies, and show that the surface anomaly is not statistically different from zero when averaged across ensembles of simulations, which we interpret as the simple fact that the volcanic impact on continental winter temperatures is tiny compared to internal variability. We also carefully examine the stratospheric pathway in our models and, again confirming previous work, show that any strengthening of the polar vortex caused by the Mt. Pinatubo eruption is very small (of the order of a few meters per second at best). Such minuscule anomalies of the stratospheric circulation are completely overwhelmed by the tropospheric variability at midlatitudes, which is known to be very large: this explains the lack of surface winter warming in the ensemble means. In summary, our analysis and interpretation offer compelling new evidence that the observed warming of the Northern Hemisphere continents in the winter 1991–1992 was very likely unrelated to the 1991 Mt. Pinatubo eruption.

Mechanisms for Global Warming Impacts on Madden–Julian Oscillation Precipitation Amplitude

2019 ◽  
Vol 32 (20) ◽  
pp. 6961-6975 ◽  
Author(s):  
Hien X. Bui ◽  
Eric D. Maloney
Keyword(s):  
Global Warming ◽  
Coupled Model ◽  
Static Stability ◽  
Moisture Gradient ◽  
Madden Julian Oscillation ◽  
Surface Warming ◽  
Moisture Advection ◽  
Diabatic Processes ◽  
Intercomparison Project ◽  
Moisture Profiles

Abstract Mechanisms that cause changes in Madden–Julian oscillation (MJO) precipitation amplitude under global warming are examined in models from phase 5 of the Coupled Model Intercomparison Project. Under global warming in representative concentration pathway 8.5, MJO precipitation intensifies in most models relative to current climate while MJO wind circulations increase at a slower rate or weaken. Changes in MJO precipitation intensity are partially controlled by changes in moisture profiles and static stability. The vertical moisture gradient increases in the lower half of the troposphere in response to the surface warming, while the vertical static stability gradient increases due to preferential warming in the upper troposphere. A nondimensional quantity called α has been defined that gives the efficiency of vertical advective moistening associated with diabatic processes in the free troposphere, and has been hypothesized by previous studies to regulate MJO amplitude. The term α is proportional to the vertical moisture gradient and inversely proportional to static stability. Under global warming, the increased vertical moisture gradient makes α larger in models, despite increased static stability. Although α increases in all models, MJO precipitation amplitude decreases in some models, contrary to expectations. It is demonstrated that in these models more top-heavy MJO diabatic heating with warming overwhelms the effect of increased α to make vertical moisture advection less efficient.

scholarly journals Northern Hemisphere continental winter warming following the 1991 Mt. Pinatubo eruption: Reconciling models and observations

2018 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Antara Banerjee ◽  
Anja Schmidt
Keyword(s):  
Northern Hemisphere ◽  
Climate Models ◽  
Climate Model ◽  
State Of The Art ◽  
Polar Vortex ◽  
Internal Variability ◽  
Simple Fact ◽  
Surface Warming ◽  
Winter Warming ◽  
Pinatubo Eruption

Abstract. It has been suggested, and is widely believed, that the anomalous surface warming observed over the Northern Hemisphere continents in the winter following the 1991 eruption of Mt. Pinatubo was, in fact, caused by that eruption, via a stratospheric pathway that involves a strengthening of the polar vortex. However, most studies that have examined multiple, state-of-the-art, coupled climate models report that, in the ensemble mean, the models do not show winter warming after the Mt. Pinatubo eruption. This lack of surface warming in the multi-model mean, concomitant with a lack of strengthening of the polar vortex, is often interpreted as a failure of the models to reproduce the observations. In this paper we show that this interpretation is erroneous, as averaging many simulations from different models, or from the same model, is not expected to yield surface anomalies similar to the observed ones, even if the models were highly accurate, owing to the presence of strong internal variability. We here analyze three large ensembles of state-of-the-art, coupled climate model simulations and show that, in all three, many individual ensemble members are able to produce Mt. Pinatubo surface warming in winter that is comparable to those observed. This establishes that current-generation climate models are perfectly capable of reproducing the observed surface post-eruption warming. We also confirm the bulk of previous studies, and show that the surface anomaly is not statistically different from zero when averaged across ensembles of simulations, which we interpret as the simple fact that the volcanic impact on continental winter temperatures is tiny compared to internal variability. We also examine the stratospheric pathway and, again confirming previous work, show that any strengthening of the polar vortex caused by the Mt. Pinatubo eruption is likely to be very small (of the order of a few m/s at best). Such minuscule anomalies of the stratospheric circulation are completely overwhelmed by the tropospheric variability at mid-latitudes, which is known to be very large: this explains the lack of surface winter warming in the ensemble means. In summary, our analysis and interpretation offers compelling new evidence that the observed warming of the Northern Hemisphere continents in the winter 1991–1992 was very likely unrelated to the 1991 Mt. Pinatubo eruption.

Tropical expansion driven by poleward advancing subtropical front

2020 ◽  
Author(s):  
Hu Yang ◽  
Gerrit Lohmann ◽  
Xiaoxu Shi ◽  
Evan J. Gowan
Keyword(s):  
Global Warming ◽  
Coupled Model ◽  
Dynamical Mechanism ◽  
Model Simulations ◽  
Subtropical Front ◽  
Surface Warming ◽  
Meridional Displacement ◽  
Intercomparison Project ◽  
The Tropics ◽  
Natural Climate

<p>Abundance of evidence shows that the tropics are expanding in the past four decades. Despite many attempts to decipher its cause, the underlying dynamical mechanism driving tropical expansion is still not clear. Here, based on observations and multi-model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5), the variations and trends of tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the meridional displacement of oceanic subtropical front. Under global warming, the subtropical ocean experiences more surface warming due to convergence of surface water. Such enhanced warming, superimposing onto the variation of Pacific Decadal Oscillation, leads to poleward advancing of subtropical front and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that the observed expanding tropics may largely attributed to the anthropogenic global warming rather than the natural climate variability.</p>

scholarly journals The PMIP4 contribution to CMIP6 – Part 3: the Last Millennium, Scientific Objective and Experimental Design for the PMIP4 <i>past1000</i> simulations

2016 ◽  
Author(s):  
Johann H. Jungclaus ◽  
Edouard Bard ◽  
Mélanie Baroni ◽  
Pascale Braconnot ◽  
Jian Cao ◽  
...  
Keyword(s):  
Collaborative Work ◽  
Coupled Model ◽  
Future Research ◽  
Model Intercomparison ◽  
Data Set ◽  
Seamless Transition ◽  
Transient Simulations ◽  
Intercomparison Project ◽  
Instrumental Period ◽  
Tier 3

Abstract. The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial time scales. This manuscript describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents: orbital, solar, volcanic, land-use/land-cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the “tier-1” (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated “tier-2” simulations. Additional experiments (“tier-3”) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This manuscript outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).

scholarly journals The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 <i>past1000</i> simulations

2017 ◽  
Vol 10 (11) ◽  
pp. 4005-4033 ◽  
Author(s):  
Johann H. Jungclaus ◽  
Edouard Bard ◽  
Mélanie Baroni ◽  
Pascale Braconnot ◽  
Jian Cao ◽  
...  
Keyword(s):  
Collaborative Work ◽  
Coupled Model ◽  
Future Research ◽  
Model Intercomparison ◽  
Data Set ◽  
Seamless Transition ◽  
Transient Simulations ◽  
Intercomparison Project ◽  
Instrumental Period ◽  
Tier 3

Abstract. The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).

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