scholarly journals Global temperature modes shed light on the Holocene temperature conundrum

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jürgen Bader ◽  
Johann Jungclaus ◽  
Natalie Krivova ◽  
Stephan Lorenz ◽  
Amanda Maycock ◽  
...  
Keyword(s):  
Global Warming ◽  
Late Holocene ◽  
Model Simulation ◽  
Volcanic Eruptions ◽  
Arctic Sea Ice ◽  
Global Temperature ◽  
Mean Annual Temperature ◽  
Cooling Mode ◽  
The Holocene ◽  
Global Mean

Abstract Reconstructions of the global mean annual temperature evolution during the Holocene yield conflicting results. One temperature reconstruction shows global cooling during the late Holocene. The other reconstruction reveals global warming. Here we show that both a global warming mode and a cooling mode emerge when performing a spatio-temporal analysis of annual temperature variability during the Holocene using data from a transient climate model simulation. The warming mode is most pronounced in the tropics. The simulated cooling mode is determined by changes in the seasonal cycle of Arctic sea-ice that are forced by orbital variations and volcanic eruptions. The warming mode dominates in the mid-Holocene, whereas the cooling mode takes over in the late Holocene. The weighted sum of the two modes yields the simulated global temperature trend evolution. Our findings have strong implications for the interpretation of proxy data and the selection of proxy locations to compute global mean temperatures.

scholarly journals Climate and marine biogeochemistry during the Holocene from transient model simulations

2018 ◽  
Vol 15 (10) ◽  
pp. 3243-3266 ◽  
Author(s):  
Joachim Segschneider ◽  
Birgit Schneider ◽  
Vyacheslav Khon
Keyword(s):  
Late Holocene ◽  
Large Scale ◽  
Model Simulation ◽  
Holocene Climate ◽  
Model Simulations ◽  
The Holocene ◽  
The Pacific ◽  
Marine Biogeochemistry ◽  
Global Mean ◽  
Atmospheric Pco2

Abstract. Climate and marine biogeochemistry changes over the Holocene are investigated based on transient global climate and biogeochemistry model simulations over the last 9500 years. The simulations are forced by accelerated and non-accelerated orbital parameters, respectively, and atmospheric pCO2, CH4, and N2O. The analysis focusses on key climatic parameters of relevance to the marine biogeochemistry, and on the physical and biogeochemical processes that drive atmosphere–ocean carbon fluxes and changes in the oxygen minimum zones (OMZs). The simulated global mean ocean temperature is characterized by a mid-Holocene cooling and a late Holocene warming, a common feature among Holocene climate simulations which, however, contradicts a proxy-derived mid-Holocene climate optimum. As the most significant result, and only in the non-accelerated simulation, we find a substantial increase in volume of the OMZ in the eastern equatorial Pacific (EEP) continuing into the late Holocene. The concurrent increase in apparent oxygen utilization (AOU) and age of the water mass within the EEP OMZ can be attributed to a weakening of the deep northward inflow into the Pacific. This results in a large-scale mid-to-late Holocene increase in AOU in most of the Pacific and hence the source regions of the EEP OMZ waters. The simulated expansion of the EEP OMZ raises the question of whether the deoxygenation that has been observed over the last 5 decades could be a – perhaps accelerated – continuation of an orbitally driven decline in oxygen. Changes in global mean biological production and export of detritus remain of the order of 10 %, with generally lower values in the mid-Holocene. The simulated atmosphere–ocean CO2 flux would result in atmospheric pCO2 changes of similar magnitudes to those observed for the Holocene, but with different timing. More technically, as the increase in EEP OMZ volume can only be simulated with the non-accelerated model simulation, non-accelerated model simulations are required for an analysis of the marine biogeochemistry in the Holocene. Notably, the long control experiment also displays similar magnitude variability to the transient experiment for some parameters. This indicates that also long control runs are required when investigating Holocene climate and marine biogeochemistry, and that some of the Holocene variations could be attributed to internal variability of the atmosphere–ocean system.

Climate variability following large volcanic eruption: CMIP6 model investigation

2021 ◽  
Author(s):  
Elizaveta Malinina ◽  
Nathan Gillett
Keyword(s):  
Climate Variability ◽  
Volcanic Eruption ◽  
Volcanic Eruptions ◽  
Arctic Sea Ice ◽  
Evaluation Tool ◽  
Global Mean Temperature ◽  
Arctic Sea ◽  
Global Mean Surface Temperature ◽  
Krakatoa Eruption ◽  
Global Mean

<p>Volcanic eruptions are an important driver of climate variability. Multiple literature sources have shown that after large explosive eruptions there is a decrease in global mean temperature, caused by an increased amount of stratospheric aerosols which influence the global radiative budget. In this study, we investigate the changes in several climate variables after a volcanic eruption. Using ESMValTool (Earth System Model Evaluation Tool) on an ensemble of historical simulations from CMIP6, such variables as global mean surface temperature (GMST), Arctic sea ice area and Nino 3.4 index were analyzed following the 1883 Krakatoa eruption. While there is a definite decrease in the multi-model mean GMST after the eruption, other indices do not show as prominent change. The reasons for this behavior are under investigation. </p>

scholarly journals Pacific variability reconciles observed and modelled global mean temperature increase since 1950

2020 ◽  
Author(s):  
Martin B. Stolpe ◽  
Kevin Cowtan ◽  
Iselin Medhaug ◽  
Reto Knutti
Keyword(s):  
Global Warming ◽  
Temperature Change ◽  
Temperature Increase ◽  
Global Temperature ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
The Pacific ◽  
Global Warming Hiatus ◽  
Warming Hiatus ◽  
Global Mean

Abstract Global mean temperature change simulated by climate models deviates from the observed temperature increase during decadal-scale periods in the past. In particular, warming during the ‘global warming hiatus’ in the early twenty-first century appears overestimated in CMIP5 and CMIP6 multi-model means. We examine the role of equatorial Pacific variability in these divergences since 1950 by comparing 18 studies that quantify the Pacific contribution to the ‘hiatus’ and earlier periods and by investigating the reasons for differing results. During the ‘global warming hiatus’ from 1992 to 2012, the estimated contributions differ by a factor of five, with multiple linear regression approaches generally indicating a smaller contribution of Pacific variability to global temperature than climate model experiments where the simulated tropical Pacific sea surface temperature (SST) or wind stress anomalies are nudged towards observations. These so-called pacemaker experiments suggest that the ‘hiatus’ is fully explained and possibly over-explained by Pacific variability. Most of the spread across the studies can be attributed to two factors: neglecting the forced signal in tropical Pacific SST, which is often the case in multiple regression studies but not in pacemaker experiments, underestimates the Pacific contribution to global temperature change by a factor of two during the ‘hiatus’; the sensitivity with which the global temperature responds to Pacific variability varies by a factor of two between models on a decadal time scale, questioning the robustness of single model pacemaker experiments. Once we have accounted for these factors, the CMIP5 mean warming adjusted for Pacific variability reproduces the observed annual global mean temperature closely, with a correlation coefficient of 0.985 from 1950 to 2018. The CMIP6 ensemble performs less favourably but improves if the models with the highest transient climate response are omitted from the ensemble mean.

Vegetation changes and associated climatic changes in the southern Altai Mountains within China during the Holocene

The Holocene ◽  
2016 ◽  
Vol 27 (5) ◽  
pp. 683-693 ◽  
Author(s):  
Zhaodong Feng ◽  
Aizhi Sun ◽  
Nurbayev Abdusalih ◽  
Min Ran ◽  
Alishir Kurban ◽  
...  
Keyword(s):  
Climatic Change ◽  
North Atlantic ◽  
Late Holocene ◽  
Mean Annual Precipitation ◽  
Mean Annual Temperature ◽  
Mountain Range ◽  
Altai Mountains ◽  
Pollen Data ◽  
The Holocene ◽  
The Pacific

The location of the Altai Mountains at the limits of both the Pacific and Atlantic influences implies that this mountain range is an important climatic boundary. Based on pollen data of 188 samples of a 390-cm core from Narenxia Peat in the southern Altai with a chronologic support of 11 accelerator mass spectrometry (AMS) dates, we reconstructed the Holocene climatic change at Narenxia Peat. The reconstruction revealed five stages of climatic change: a cold and dry latest deglacial (prior to ~11,500 cal. yr BP), a warm and wet early-Holocene (~11,500 to ~7000 cal. yr BP), a considerably cooled and dried middle Holocene (~7000 to ~4000 cal. yr BP), a resumed warm and wet late-Holocene (~4000 to ~1200 cal. yr BP), and a relatively cool and dry latest Holocene (past ~1200 years). The reconstructions of mean annual temperature (MAT) and mean annual precipitation (MAP) from Narenxia Peat well resemble the reconstructions of North Atlantic Oscillations (NAO) and El Niño–Southern Oscillations (ENSO). The resemblance implies that the Holocene millennial-scale changes in MAT and MAP in the Altai might have been causally associated with the variations in NAO and ENSO.

scholarly journals Long-term variations in Iceland–Scotland overflow strength during the Holocene

2013 ◽  
Vol 9 (2) ◽  
pp. 1627-1656 ◽  
Author(s):  
D. J. R. Thornalley ◽  
M. Blaschek ◽  
F. J. Davies ◽  
S. Praetorius ◽  
D. W. Oppo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Late Holocene ◽  
Deep Convection ◽  
Arctic Sea Ice ◽  
Global Ocean ◽  
Nordic Seas ◽  
Model Simulations ◽  
The Holocene ◽  
Arctic Sea

Abstract. The overflow of deep water from the Nordic Seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland–Scotland (I–S) overflow, yet the history of its strength throughout the Holocene (~0–11 700 yr ago, ka) is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I–S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland basin. Our results reveal weaker I–S overflow during the early and late Holocene, with maximum overflow strength occurring at ~7 ka, the time of a regional climate thermal maximum. Climate model simulations suggest a shoaling of deep convection in the Nordic Seas during the early and late Holocene, consistent with our evidence for weaker I–S overflow during these intervals. Whereas the reduction in I–S overflow strength during the early Holocene likely resulted from melting remnant glacial ice-sheets, the decline throughout the last 7000 yr was caused by an orbitally-induced increase in the amount of Arctic sea-ice entering the Nordic Seas. Although the flux of Arctic sea-ice to the Nordic Seas is expected to decrease throughout the next century, model simulations predict that under high emissions scenarios, competing effects, such as warmer sea surface temperatures in the Nordic Seas, will result in reduced deep convection, likely driving a weaker I–S overflow.

Comparing temperature trends and variability over the Holocene in climate models of low and high complexity

2021 ◽  
Author(s):  
Christian Wirths ◽  
Elisa Ziegler ◽  
Matthew Toohey ◽  
Julie Christin Schindlbeck-Belo ◽  
Steffen Kutterolf ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Volcanic Eruptions ◽  
Arctic Sea Ice ◽  
Balance Model ◽  
Earth System ◽  
Holocene Climate ◽  
Model Simulations ◽  
The Holocene ◽  
Temperature Trends ◽  
Proxy Reconstructions

<div> <p>Modeled and observed temperature trends over the Holocene disagree. Proxy reconstructions suggest global cooling during the late Holocene. Model simulations, on the other hand, show a warming trend for the entire Holocene, a contradiction known as the Holocene temperature conundrum.  </p> </div><div> <p>A recent study by Bader et. al. (2020) introduced a new approach to the question by proposing the coexistence of a cooling and warming climate mode. While the warming mode is proposed to be related to changes in greenhouse gas concentrations, the physical process behind the cooling mode might be a change in the seasonal cycle of Arctic sea-ice. It’s unclear to what extent this process is responsible for the observed climate response. Depending on their strength and location these modes have strong implications for proxy data interpretation and location selection when calculating global mean temperatures.   </p> </div><div> <p>Here, we investigate if similar modes and temperature trends can be found in models of different complexity. Therefore, we use a 2D Energy Balance Model (EBM), with solar, volcanic, ice-sheet and greenhouse gas forcing, for transient simulations of the Holocene climate. We analyze these Holocene climate simulations in terms of global and regional temperature trends, modes and variability patterns. We conduct sensitivity tests to examine the influence of the forcings on those trends and modes. In particular, we are interested in the influence of volcanic eruptions on the Holocene climate. Furthermore, we compare our model results with temperature reconstructions and simulations from Earth System Models.    </p> </div><div> <p>Altogether, we comprehensively analyze Holocene climate as simulated by a conceptual EBM, a state-of-the-art Earth System Model and proxy reconstructions. The results provide insight into whether models of different complexity produce similar modes and trends and whether these occur due to climate forcing rather than internal processes of the earth system. Finally, we will provide a better understanding of Holocene cooling and warming and the interpretation of differences between Holocene temperature proxy reconstructions and climate model simulations.    </p> </div><div> <p> </p> </div><div> <p>References:  <br>Bader, J., Jungclaus, J., Krivova, N. et al. Global temperature modes shed light on the Holocene temperature conundrum. Nat Commun 11, 4726 (2020). https://doi.org/10.1038/s41467-020-18478-6 </p> </div>

scholarly journals Climate and marine biogeochemistry during the Holocene from transient model simulations

2018 ◽  
Author(s):  
Joachim Segschneider ◽  
Birgit Schneider ◽  
Vyacheslav Khon
Keyword(s):  
Late Holocene ◽  
Large Scale ◽  
Water Mass ◽  
Model Simulation ◽  
Anthropogenic Forcing ◽  
Model Simulations ◽  
The Holocene ◽  
Marine Biogeochemistry ◽  
Ocean Atmosphere ◽  
Atmospheric Pco2

Abstract. Climate and marine biogeochemistry changes over the Holocene are investigated based on transient global climate and biogeochemistry model simulations over the last 9,500 yr. The simulations are forced by accelerated and non-accelerated orbital parameters, respectively, and atmospheric pCO2. The analysis focusses on key climatic parameters of relevance to the marine biogeochemistry, on the processes that determine the strength of the carbon pumps that drive the ocean–atmosphere carbon flux, and on the oxygen minimum zones (OMZs) in the ocean. The most pronounced changes occur in the eastern equatorial Pacific (EEP) OMZ, and in the North Atlantic. Changes in global mean values of biological production and export of detritus remain modest, with generally lower values in the mid-Holocene. The simulated ocean–atmosphere CO2-flux is of the right order of magnitude to explain the observed atmospheric pCO2 evolution, but with different timing. As the most significant result, we find a substantial increase in volume of the OMZ in the EEP continuing into the late Holocene in the non-accelerated simulation. The concurrent increase of age of the water mass within the EEP OMZ suggests that this growth is driven by a slow down of the circulation in the interior of the deep Pacific. This results in large scale deoxygenation in the deeper Pacific and hence the source regions of the EEP OMZ waters from mid-to-late Holocene. The simulated expansion of the OMZ raises the question whether the currently observed deoxygenation is a continuation of the orbitally driven decline in oxygen, or if it is already a result of the occuring climate change from anthropogenic forcing as widely assumed. An additional explanation would be that the anthropogenic forcing amplifies the natural forcing. The increase in water mass age and EEP OMZ volume can only be simulated with the non-accelerated model simulation. The simulations thus demonstrate that non-accelerated experiments are required for an analysis of the marine biogeochemistry in the Holocene.

scholarly journals Long-term variations in Iceland–Scotland overflow strength during the Holocene

2013 ◽  
Vol 9 (5) ◽  
pp. 2073-2084 ◽  
Author(s):  
D. J. R. Thornalley ◽  
M. Blaschek ◽  
F. J. Davies ◽  
S. Praetorius ◽  
D. W. Oppo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Late Holocene ◽  
Deep Convection ◽  
Arctic Sea Ice ◽  
Early Holocene ◽  
Nordic Seas ◽  
Model Simulations ◽  
The Holocene ◽  
Arctic Sea

Abstract. The overflow of deep water from the Nordic seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland–Scotland (I–S) overflow, yet the history of its strength throughout the Holocene (~ 0–11 700 yr ago, ka) is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I–S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland Basin. Our data are consistent with the hypothesis that the main axis of the I–S overflow on the Iceland slope was shallower during the early Holocene, deepening to its present depth by ~ 7 ka. Our results also reveal weaker I–S overflow during the early and late Holocene, with maximum overflow strength occurring at ~ 7 ka, the time of a regional climate thermal maximum. Climate model simulations suggest a shoaling of deep convection in the Nordic seas during the early and late Holocene, consistent with our evidence for weaker I–S overflow during these intervals. Whereas the reduction in I–S overflow strength during the early Holocene likely resulted from melting remnant glacial ice sheets, the decline throughout the last 7000 yr was caused by an orbitally induced increase in the amount of Arctic sea ice entering the Nordic seas. Although the flux of Arctic sea ice to the Nordic seas is expected to decrease throughout the next century, model simulations predict that under high emissions scenarios, competing effects, such as warmer sea surface temperatures in the Nordic seas, will result in reduced deep convection, likely driving a weaker I–S overflow.

scholarly journals Current rapid global temperature rise linked to falling SO<sub>2</sub> emissions

2018 ◽  
Author(s):  
Nick E. B. Cowern
Keyword(s):  
Heat Exchange ◽  
Solar Irradiance ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
Global Temperature ◽  
Climate Forcing ◽  
Accurate Estimation ◽  
Tropospheric Aerosol ◽  
Ocean Atmosphere ◽  
Global Mean

Abstract. It is widely held that global temperature variations on time scales of a decade or less are primarily caused by internal climate variability, with smaller contributions from changes in external climate forcing such as solar irradiance. This paper shows that observed variations in global mean surface temperature, TGS, and ocean heat content (OHC) during the last 1–2 decades imply major changes in climate forcing during this period. In a first step, two independent methods are used to evaluate global temperature corrected for ocean–atmosphere heat exchange. El Niño/Southern Oscillation (ENSO) corrected TGS (written as TGS) is shown to agree closely with a novel temperature metric θ that combines uncorrected TGS with scaled OHC. This agreement rules out a substantial 21st-century contribution to TGS from ocean-atmosphere heat exchange. In contrast to TGS, the time series TGS (t) provides a clear fingerprint of transient global cooling associated with major volcanic eruptions, enabling a more accurate empirical estimate of the climate response of the global mean surface. This allows more accurate estimation of the net climate forcing by stratospheric aerosols and solar irradiance, which is then subtracted from TGS (t) to determine the underlying signal of anthropogenic global warming. Key features of this signal are a slowdown from the late 1990s to 2011 – corresponding to the well known climate hiatus – and a subsequent sharp upturn indicating a steep increase in anthropogenic climate forcing. It is argued that the only plausible cause for this increase is a large fractional decrease in tropospheric aerosol cooling. This attribution is supported by satellite-based observations of a > 50 % decrease in SO2 emissions from large sources during the last six years. It suggests that current clean-air policies and replacement of coal by natural gas are driving a significant human made climatic event, 2–4 times faster than greenhouse driven warming alone. If confirmed, this implies a considerably shortened timescale to meet the IPCC 1.5 °C objective, with major implications for near-term carbon emission policies.

Holocene chronology and tephrostratigraphy for the varved record of Lake Diss Mere (UK)

2020 ◽  
Author(s):  
Celia Martin-Puertas ◽  
Amy Walsh ◽  
Simon P.E Blockley ◽  
George E. Biddulph ◽  
Adrian Palmer ◽  
...  
Keyword(s):  
Late Holocene ◽  
Ice Core ◽  
Volcanic Eruptions ◽  
Laminated Sediments ◽  
British Isles ◽  
Radiocarbon Dates ◽  
The Holocene ◽  
Planktonic Diatoms ◽  
Tephra Layers ◽  
Diatom Blooms

&lt;p&gt;The lacustrine record of Lake Diss Mere, Norfolk (UK) is 15 m long, and shows 4.2 m of finely-laminated sediments, which are present between 9 and 13 m of core depth. The microfacies analysis identified three major seasonal patterns of deposition (microfacies 1 &amp;#8211; 3), which corroborate the annual nature of sedimentation throughout the whole interval. The sediments are diatomaceous organic and carbonate varves with an average thickness of 0.45 mm. Microfacies 1 consists of a pale layer made of authigenic calcite crystals and diatom frustules, and a dark layer composed of a planktonic diatoms and filaments of organic matter. Microfacies 2 is similar to microfacies 1 but includes a mono-specific diatom bloom layer preceding the calcite layer. Microfacies 3 are varves with an occasional very thin calcite layer and mono-specific diatom blooms in spring and autumn.&lt;/p&gt;&lt;p&gt;A total of 8252 varves were counted with an error of up to &amp;#160;27 varves. To tie the resulting floating varve chronology to the IntCal 2013 radiocarbon timescale, we used a Bayesian Deposition model (P_Sequence with outlier detection) on all available chronological data. The data included seven radiocarbon dates, six tephra layers with known radiocarbon ages, and the relative varve counts between dated points. The resulting age&amp;#160;uncertainties are decadal in scale (95% confidence) and allow detailed comparisons to other high-resolution Holocene varved lake and ice-core records on absolute timescales. The potential for this record as a palaeoclimate archive for the British Isles is enhanced by the Glen Garry&lt;sup&gt;1&lt;/sup&gt;(2172 &amp;#177;&amp;#160;107 cal a BP) and OMH-185&lt;sup&gt;2&lt;/sup&gt;(2667 &amp;#177; 38 cal a BP) volcanic eruptions which lie amongst 3 further late-Holocene cryptotephra layers at &lt;em&gt;ca&lt;/em&gt; 2400 cal a BP, 2540 cal a BP, and 3870 cal a BP, and a mid-Holocene cryptotephra layers at &lt;em&gt;ca&lt;/em&gt; 6420 cal a BP. Initial investigations and geochemical characterisation suggest Icelandic eruption centres for these cryptotephra layers which are known to be present in sites in the British Isles and elsewhere in Europe.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1 &lt;/sup&gt;Barber, K., Langdon, P., Blundell, A. Dating the Glen Garry tephra: a widespread late-Holocene marker horizon in the peatlands of northern Britain. The Holocene, 18: 31-43. 2008.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&amp;#160;&lt;/sup&gt;Plunkett, G.M., Pilcher, J.R., McCormac, F.G., Hall, V.A. New dates for first millennium BC tephra isochrones in Ireland. The Holocene, 14: 780-786. 2004&lt;/p&gt;

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