scholarly journals Understanding drivers of glacier-length variability over the last millennium

2021 ◽  
Vol 15 (3) ◽  
pp. 1645-1662
Author(s):  
Alan Huston ◽  
Nicholas Siler ◽  
Gerard H. Roe ◽  
Erin Pettit ◽  
Nathan J. Steiger
Keyword(s):  
Climate Variability ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Forced Response ◽  
Last Millennium ◽  
External Forcing ◽  
Climate History ◽  
Temperature And Precipitation ◽  
Glacier Length

Abstract. Changes in glacier length reflect the integrated response to local fluctuations in temperature and precipitation resulting from both external forcing (e.g., volcanic eruptions or anthropogenic CO2) and internal climate variability. In order to interpret the climate history reflected in the glacier moraine record, the influence of both sources of climate variability must therefore be considered. Here we study the last millennium of glacier-length variability across the globe using a simple dynamic glacier model, which we force with temperature and precipitation time series from a 13-member ensemble of simulations from a global climate model. The ensemble allows us to quantify the contributions to glacier-length variability from external forcing (given by the ensemble mean) and internal variability (given by the ensemble spread). Within this framework, we find that internal variability is the predominant source of length fluctuations for glaciers with a shorter response time (less than a few decades). However, for glaciers with longer response timescales (more than a few decades) external forcing has a greater influence than internal variability. We further find that external forcing also dominates when the response of glaciers from widely separated regions is averaged. Single-forcing simulations indicate that, for this climate model, most of the forced response over the last millennium, pre-anthropogenic warming, has been driven by global-scale temperature change associated with volcanic aerosols.

scholarly journals Understanding Drivers of Glacier Length Variability Over the Last Millennium

2020 ◽  
Author(s):  
Alan Huston ◽  
Nicholas Siler ◽  
Gerard H. Roe ◽  
Erin Pettit ◽  
Nathan J. Steiger
Keyword(s):  
Climate Variability ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Forced Response ◽  
Last Millennium ◽  
External Forcing ◽  
Climate History ◽  
Temperature And Precipitation ◽  
Glacier Length ◽  
Length Changes

Abstract. Changes in glacier length reflect the integrated response to local fluctuations in temperature and precipitation resulting from both external forcing (e.g., volcanic eruptions or anthropogenic CO2) and internal climate variability. In order to interpret the climate history reflected in the glacier moraine record, therefore, the influence of both sources of climate variability must be considered. Here we study the last millennium of glacier length variability across the globe using a simple dynamic glacier model, which we force with temperature and precipitation time series from a 13-member ensemble of simulations from a global climate model. The ensemble allows us to quantify the contributions to glacier length variability from external forcing (given by the ensemble mean) and internal variability (given by the ensemble spread). Within this framework, we find that internal variability drives most length changes in mountain glaciers that have a response timescale of less than a few decades. However, for glaciers with longer response timescales (more than a few decades) external forcing has a greater influence than internal variability. We further find that external forcing also dominates when the response of glaciers from widely separated regions is averaged. Single-forcing simulations indicate that most of the forced response over the last millennium, pre-anthropogenic warming, has been driven by global-scale temperature change associated with volcanic aerosols.

scholarly journals The early Spörer Minimum – a period of extraordinary climate and socio-economic changes in Western and Central Europe

2016 ◽  
Author(s):  
Chantal Camenisch ◽  
Kathrin M. Keller ◽  
Melanie Salvisberg ◽  
Benjamin Amann ◽  
Martin Bauch ◽  
...  
Keyword(s):  
Climate Variability ◽  
Central Europe ◽  
Climate Model ◽  
Internal Variability ◽  
Climatic Conditions ◽  
Food Prices ◽  
External Forcing ◽  
Adaptation Measures ◽  
Model Simulations ◽  
15Th Century

Abstract. Throughout the last millennium, mankind was affected by prolonged deviations from the climate mean state. While periods like the Maunder Minimum in the 17th century have been assessed in greater detail, earlier cold periods such as the 15th century received much less attention due to the sparse information available. Based on new evidence from different sources ranging from proxy archives to model simulations, it is now possible to provide an end-to-end assessment about the climate state during an exceptionally cold period in the 15th century, the role of internal, unforced climate variability and external forcing in shaping these extreme climatic conditions, and the impacts on and responses of the medieval society in Central Europe. Climate reconstructions from a multitude of natural and human archives indicate that, during winter, the period of the early Spörer Minimum (1431–1440 CE) was the coldest decade in Central Europe in the 15th century. The particularly cold winters and normal but wet summers resulted in a strong seasonal cycle that challenged food production and led to increasing food prices, a subsistence crisis, and a famine in parts of Europe. As a consequence, authorities implemented adaptation measures, such as the installation of grain storage capacities, in order to be prepared for future events. The 15th century is characterised by a grand solar minimum and enhanced volcanic activity, which both imply a reduction of seasonality. Climate model simulations show that periods with cold winters and strong seasonality are associated with internal climate variability rather than external forcing. Accordingly, it is hypothesised that the reconstructed extreme climatic conditions during this decade occurred by chance and in relation to the partly chaotic, internal variability within the climate system.

Application of linear dynamical mode decomposition to ensembles of climate simulations

2021 ◽  
Author(s):  
Maria Buyanova ◽  
Sergey Kravtsov ◽  
Andrey Gavrilov ◽  
Dmitry Mukhin ◽  
Evgeny Loskutov ◽  
...  
Keyword(s):  
Time Series ◽  
Climate Variability ◽  
20Th Century ◽  
Time Scales ◽  
Principal Components ◽  
Internal Variability ◽  
Forced Response ◽  
Climate System ◽  
External Forcing ◽  
Function Decomposition

<p>An analysis of the climate system is usually complicated by its very high dimensionality and its nonlinearity which impedes spatial and time scale separation. An even more difficult problem is to obtain separate estimates of the climate system’s response to external forcing (e.g. anthropogenic emissions of greenhouse gases and aerosols) and the contribution of the climate system’s internal variability into recent climate trends. Identification of spatiotemporal climatic patterns representing forced signals and internal variability in global climate models (GCMs) would make it possible to characterize these patterns in the observed data and to analyze dynamical relationships between these two types of climate variability.</p><p>In contrast with real climate observations, many GCMs are able to provide ensembles of many climate realizations under the same external forcing, with relatively independent initial conditions (e.g. LENS [1], MPI-GE [2], CMIP ensembles of 20th century climate). In this report, a recently developed method of empirical spatio-temporal data decomposition into linear dynamical modes (LDMs) [3] based on Bayesian approach, is modified to address the problem of self-consistent separation of the climate system internal variability modes and the forced response signals in such ensembles. The LDM method provides the time series of principal components and corresponding spatial patterns; in application to an ensemble of realizations, it determines both time series of the internal variability modes of current realization and the time series of forced response (defined as signal shared by all realizations). The advantage of LDMs is the ability to take into account the time scales of the system evolution better than some other linear techniques, e.g. traditional empirical orthogonal function decomposition. Furthermore, the modified ensemble LDM (E-LDM) method is designed to determine the optimal number of principal components and to distinguish their time scales for both internal variability modes and forced response signals.</p><p>The technique and results of applying LDM method to different GCM ensemble realizations will be presented and discussed. This research was supported by the Russian Science Foundation (Grant No. 18-12-00231).</p><p>[1] Kay, J. E., Deser, C., Phillips, A., Mai, A., Hannay, C., Strand, G., Arblaster, J., Bates, S., Danabasoglu, G., Edwards, J., Holland, M. Kushner, P., Lamarque, J.-F., Lawrence, D., Lindsay, K., Middleton, A., Munoz, E., Neale, R., Oleson, K., Polvani, L., and M. Vertenstein (2015), The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability, Bulletin of the American Meteorological Society, doi: 10.1175/BAMS-D-13-00255.1, 96, 1333-1349 </p><p>[2] Maher, N., Milinski, S., Suarez-Gutierrez, L., Botzet, M., Dobrynin, M., Kornblueh, L., Kröger, J., Takano, Y., Ghosh, R., Hedemann, C., Li, C., Li, H., Manzini, E., Notz, N., Putrasahan, D., Boysen, L., Claussen, M., Ilyina, T., Olonscheck, D., Raddatz, T., Stevens, B. and Marotzke, J. (2019). The Max Planck Institute Grand Ensemble: Enabling the Exploration of Climate System Variability. Journal of Advances in Modeling Earth Systems, 11, 1-21. https://doi.org/10.1029/2019MS001639</p><p>[3] Gavrilov, A., Kravtsov, S., Mukhin, D. (2020). Analysis of 20th century surface air temperature using linear dynamical modes. Chaos: An Interdisciplinary Journal of Nonlinear Science, 30(12), 123110. https://doi.org/10.1063/5.0028246</p>

scholarly journals Separating Forced from Chaotic Climate Variability over the Past Millennium

2013 ◽  
Vol 26 (18) ◽  
pp. 6954-6973 ◽  
Author(s):  
Andrew P. Schurer ◽  
Gabriele C. Hegerl ◽  
Michael E. Mann ◽  
Simon F. B. Tett ◽  
Steven J. Phipps
Keyword(s):  
Climate Variability ◽  
Volcanic Eruptions ◽  
Forced Response ◽  
Ice Age ◽  
Mean Annual Temperature ◽  
External Forcing ◽  
The Past ◽  
Hemispheric Temperature ◽  
Wide Range ◽  
Past Millennium

Abstract Reconstructions of past climate show notable temperature variability over the past millennium, with relatively warm conditions during the Medieval Climate Anomaly (MCA) and a relatively cold Little Ice Age (LIA). Multimodel simulations of the past millennium are used together with a wide range of reconstructions of Northern Hemispheric mean annual temperature to separate climate variability from 850 to 1950 CE into components attributable to external forcing and internal climate variability. External forcing is found to contribute significantly to long-term temperature variations irrespective of the proxy reconstruction, particularly from 1400 onward. Over the MCA alone, however, the effect of forcing is only detectable in about half of the reconstructions considered, and the response to forcing in the models cannot explain the warm conditions around 1000 CE seen in some reconstructions. The residual from the detection analysis is used to estimate internal variability independent from climate modeling, and it is found that the recent observed 50- and 100-yr hemispheric temperature trends are substantially larger than any of the internally generated trends even using the large residuals over the MCA. Variations in solar output and explosive volcanism are found to be the main drivers of climate change from 1400 to 1900, but for the first time a significant contribution from greenhouse gas variations to the cold conditions during 1600–1800 is also detected. The proxy reconstructions tend to show a smaller forced response than is simulated by the models. This discrepancy is shown, at least partly, to be likely associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations.

scholarly journals Emerging Anthropogenic Influences on the Southcentral Alaska Temperature and Precipitation Extremes and Related Fires in 2019

Land ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 82
Author(s):  
Uma S. Bhatt ◽  
Rick T. Lader ◽  
John E. Walsh ◽  
Peter A. Bieniek ◽  
Richard Thoman ◽  
...  
Keyword(s):  
Climate Model ◽  
Simulation Analysis ◽  
Historical Context ◽  
Fire Risk ◽  
Internal Variability ◽  
Fire Season ◽  
Temperature And Precipitation ◽  
Southcentral Alaska ◽  
Meteorological Observations ◽  
Climate Model Simulations

The late-season extreme fire activity in Southcentral Alaska during 2019 was highly unusual and consequential. Firefighting operations had to be extended by a month in 2019 due to the extreme conditions of hot summer temperature and prolonged drought. The ongoing fires created poor air quality in the region containing most of Alaska’s population, leading to substantial impacts to public health. Suppression costs totaled over $70 million for Southcentral Alaska. This study’s main goals are to place the 2019 season into historical context, provide an attribution analysis, and assess future changes in wildfire risk in the region. The primary tools are meteorological observations and climate model simulations from the NCAR CESM Large Ensemble (LENS). The 2019 fire season in Southcentral Alaska included the hottest and driest June–August season over the 1979–2019 period. The LENS simulation analysis suggests that the anthropogenic signal of increased fire risk had not yet emerged in 2019 because of the CESM’s internal variability, but that the anthropogenic signal will emerge by the 2040–2080 period. The effect of warming temperatures dominates the effect of enhanced precipitation in the trend towards increased fire risk.

scholarly journals Simulated climate variability in the region of Rapa Nui during the last millennium

2011 ◽  
Vol 7 (1) ◽  
pp. 381-395 ◽  
Author(s):  
C. Junk ◽  
M. Claussen
Keyword(s):  
Large Scale ◽  
Vegetation Change ◽  
Climate Model ◽  
Volcanic Eruptions ◽  
Easter Island ◽  
Ice Age ◽  
Vegetation Changes ◽  
Last Millennium ◽  
Climate Data ◽  
Climatic Fluctuations

Abstract. Easter Island, an isolated island in the Southeast Pacific, was settled by the Polynesians probably between 600 and 1200 AD and discovered by the Europeans in 1722 AD. While the Polynesians presumably found a profuse palm woodland on Easter Island, the Europeans faced a landscape dominated by grassland. Scientists have examined potential anthropogenic, biological and climatic induced vegetation changes on Easter Island. Here, we analyze observational climate data for the last decades and climate model results for the period 800–1750 AD to explore potential causes for a climatic-induced vegetation change. A direct influence of the ENSO phenomenon on the climatic parameters of Easter Island could not be found in the model simulations. Furthermore, strong climatic trends from a warm Medieval Period to a Little Ice Age or rapid climatic fluctuations due to large volcanic eruptions were not verifiable for the Easter Island region, although they are detectable in the simulations for many regions world wide. Hence we tentatively conclude that large-scale climate changes in the oceanic region around Easter Island might be too small to explain strong vegetation changes on the island over the last millennium.

scholarly journals How Do Volcanic Eruptions Influence Decadal Megadroughts over Eastern China?

2020 ◽  
Vol 33 (19) ◽  
pp. 8195-8207 ◽  
Author(s):  
Liang Ning ◽  
Kefan Chen ◽  
Jian Liu ◽  
Zhengyu Liu ◽  
Mi Yan ◽  
...  
Keyword(s):  
Asian Summer Monsoon ◽  
Eastern China ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Last Millennium ◽  
Decadal Scale ◽  
Community Earth System Model ◽  
Sea Surface Temperature Anomalies ◽  
Asian Summer ◽  
The Western Pacific

AbstractThe influence and mechanism of volcanic eruptions on decadal megadroughts over eastern China during the last millennium were investigated using a control (CTRL) and five volcanic eruption sensitivity experiments (VOLC) from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive. The decadal megadroughts associated with the failures of the East Asian summer monsoon (EASM) are associated with a meridional tripole of sea surface temperature anomalies (SSTAs) in the western Pacific from the equator to high latitudes, suggestive of a decadal-scale internal mode of variability that emerges from empirical orthogonal function (EOF) analysis. Composite analyses further showed that, on interannual time scales, within a decade after an eruption the megadrought was first enhanced but then weakened, due to the change from an El Niño state to a La Niña state. The impacts of volcanic eruptions on the magnitudes of megadroughts are superposed on internal variability. Therefore, the evolution of decadal megadroughts coinciding with strong volcanic eruptions demonstrate that the impacts of internal variability and external forcing can combine to influence hydroclimate.

scholarly journals Climate and carbon cycle dynamics in a CESM simulation from 850–2100 CE

2015 ◽  
Vol 6 (1) ◽  
pp. 351-406 ◽  
Author(s):  
F. Lehner ◽  
F. Joos ◽  
C. C. Raible ◽  
J. Mignot ◽  
A. Born ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Total Solar Irradiance ◽  
Historical Period ◽  
Last Millennium ◽  
Coupled Modelling ◽  
Decadal Scale ◽  
Current Century ◽  
Ocean Carbon

Abstract. Under the protocols of the Paleoclimate and Coupled Modelling Intercomparison Projects a number of simulations were produced that provide a range of potential climate evolutions from the last millennium to the end of the current century. Here, we present the first simulation with the Community Earth System Model (CESM), which includes an interactive carbon cycle, that continuously covers the last millennium, the historical period, and the twenty-first century. Besides state-of-the-art forcing reconstructions, we apply a modified reconstruction of total solar irradiance to shed light on the issue of forcing uncertainty in the context of the last millennium. Nevertheless, we find that structural uncertainties between different models can still dominate over forcing uncertainty for quantities such as hemispheric temperatures or the land and ocean carbon cycle response. Comparing with other model simulations we find forced decadal-scale variability to occur mainly after volcanic eruptions, while during other periods internal variability masks potentially forced signals and calls for larger ensembles in paleoclimate modeling studies. At the same time, we fail to attribute millennial temperature trends to orbital forcing, as has been suggested recently. The climate-carbon cycle sensitivity in CESM during the last millennium is estimated to be about 1.3 ppm °C−1. However, the dependence of this sensitivity on the exact time period and scale illustrates the prevailing challenge of deriving robust constrains on this quantity from paleoclimate proxies. In particular, the response of the land carbon cycle to volcanic forcing shows fundamental differences between different models. In CESM the tropical land dictates the response to volcanoes with a distinct behavior for large and moderate eruptions. Under anthropogenic emissions, global land and ocean carbon uptake rates emerge from the envelope of interannual natural variability as simulated for the last millennium by about year 1947 and 1877, respectively.

Global and amplified land warming trends over the past 40+ years are entirely human-driven.

2021 ◽  
Author(s):  
Karsten Haustein
Keyword(s):  
Radiative Forcing ◽  
Volcanic Eruptions ◽  
Internal Variability ◽  
Forced Response ◽  
Global Temperature ◽  
Extreme Weather Events ◽  
Temperature Record ◽  
Model Framework ◽  
Anthropogenic Aerosol ◽  
The Past

<p class="p1">The role of external (radiative) forcing factors and internal unforced (ocean) low-frequency variations in the instrumental global temperature record are still hotly debated. More recent findings point towards a larger contribution from changes in external forcing, but the jury is still out. While the estimation of the human-induced total global warming fraction since pre-industrial times is fairly robust and mostly independent of multidecadal internal variability, this is not necessarily the case for key regional features such as Arctic amplification or enhanced warming over continental land areas. Accounting for the slow global temperature adjustment after strong volcanic eruptions, the spatially heterogeneous nature of anthropogenic aerosol forcing and known biases in the sea surface temperature record, almost all of the multidecadal fluctuations observed over at least the last 160+ years can be explained without a relevant role for internal variability. Using a two-box response model framework, I will demonstrate that not only multidecadal variability is very likely a forced response, but warming trends over the past 40+ years are entirely attributable to human factors. Repercussions for amplifed European (or D-A-CH for that matter) warming and associated implications for extreme weather events are discussed. Further consideration is given to the communications aspect of such critical results as well as the question of wider societal impacts.</p>

scholarly journals Large-scale temperature response to external forcing in simulations and reconstructions of the last millennium

2013 ◽  
Vol 9 (1) ◽  
pp. 393-421 ◽  
Author(s):  
L. Fernández-Donado ◽  
J. F. González-Rouco ◽  
C. C. Raible ◽  
C. M. Ammann ◽  
D. Barriopedro ◽  
...  
Keyword(s):  
Internal Variability ◽  
Ice Age ◽  
Future Climate Change ◽  
Last Millennium ◽  
External Forcing ◽  
Transient Climate Response ◽  
Temperature Changes ◽  
Model Simulations ◽  
Major Player ◽  
Intercomparison Project

Abstract. Understanding natural climate variability and its driving factors is crucial to assessing future climate change. Therefore, comparing proxy-based climate reconstructions with forcing factors as well as comparing these with paleoclimate model simulations is key to gaining insights into the relative roles of internal versus forced variability. A review of the state of modelling of the climate of the last millennium prior to the CMIP5–PMIP3 (Coupled Model Intercomparison Project Phase 5–Paleoclimate Modelling Intercomparison Project Phase 3) coordinated effort is presented and compared to the available temperature reconstructions. Simulations and reconstructions broadly agree on reproducing the major temperature changes and suggest an overall linear response to external forcing on multidecadal or longer timescales. Internal variability is found to have an important influence at hemispheric and global scales. The spatial distribution of simulated temperature changes during the transition from the Medieval Climate Anomaly to the Little Ice Age disagrees with that found in the reconstructions. Thus, either internal variability is a possible major player in shaping temperature changes through the millennium or the model simulations have problems realistically representing the response pattern to external forcing. A last millennium transient climate response (LMTCR) is defined to provide a quantitative framework for analysing the consistency between simulated and reconstructed climate. Beyond an overall agreement between simulated and reconstructed LMTCR ranges, this analysis is able to single out specific discrepancies between some reconstructions and the ensemble of simulations. The disagreement is found in the cases where the reconstructions show reduced covariability with external forcings or when they present high rates of temperature change.

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