scholarly journals Investigating vegetation-climate feedbacks during the early Eocene

2013 ◽  
Vol 9 (4) ◽  
pp. 4705-4744
Author(s):  
C. A. Loptson ◽  
D. J. Lunt ◽  
J. E. Francis
Keyword(s):  
Water Vapour ◽  
Global Scale ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Climate Feedbacks ◽  
Modelling Framework ◽  
Modelling Studies ◽  
Balance Analysis ◽  
Energy Balance Analysis

Abstract. Evidence suggests that the early Eocene was a time of extreme global warmth, extending to the high latitudes. However, there are discrepancies between the results of many previous modelling studies and the proxy data at high latitudes, with models struggling to simulate the shallow temperature gradients of this time period to the same extent as the proxies indicate. Vegetation-climate feedbacks play an important role in the present day, but are often neglected in paleoclimate modelling studies and this may be a contributing factor to resolving the model-data discrepancy. Here we investigate these vegetation-climate feedbacks by carrying out simulations of the early Eocene climate at 2 × and 4 × pre-industrial atmospheric CO2 with fixed vegetation (homogeneous shrubs everywhere) and dynamic vegetation. The results show that the simulations with dynamic vegetation are warmer in the global annual mean than the simulations with fixed shrubs by 0.9 °C at 2 × and 1.8 °C at 4 ×. In addition, the warming when CO2 is doubled from 2 × to 4 × is 1 °C higher (in the global annual mean) with dynamic vegetation than with fixed shrubs. This corresponds to an increase in climate sensitivity of 26%. This difference in warming is enhanced at high latitudes, with temperatures increasing by over 50% in some regions of Antarctica. In the Arctic, ice-albedo feedbacks are responsible for the majority of this warming. On a global scale, energy balance analysis shows that the enhanced warming with dynamic vegetation is mainly associated with an increase in atmospheric water vapour but changes in clouds also contribute to the temperature increase. It is likely that changes in surface albedo due to changes in vegetation cover resulted in an initial warming which triggered these water vapour feedbacks. In conclusion, dynamic vegetation goes some way to resolving the discrepancy, but our modelled temperatures cannot reach the same warmth as the data suggests in the Arctic. This suggests that there are additional mechanisms, not included in this modelling framework, behind the polar warmth.

scholarly journals Investigating vegetation–climate feedbacks during the early Eocene

2014 ◽  
Vol 10 (2) ◽  
pp. 419-436 ◽  
Author(s):  
C. A. Loptson ◽  
D. J. Lunt ◽  
J. E. Francis
Keyword(s):  
Water Vapour ◽  
Global Scale ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Climate Feedbacks ◽  
Modelling Framework ◽  
Modelling Studies ◽  
Balance Analysis ◽  
Energy Balance Analysis

Abstract. Evidence suggests that the early Eocene was a time of extreme global warmth. However, there are discrepancies between the results of many previous modelling studies and the proxy data at high latitudes, with models struggling to simulate the shallow temperature gradients of this time period to the same extent as the proxies indicate. Vegetation–climate feedbacks play an important role in the present day, but are often neglected in these palaeoclimate modelling studies, and this may be a contributing factor to resolving the model–data discrepancy. Here we investigate these vegetation–climate feedbacks by carrying out simulations of the early Eocene climate at 2 × and 4 × pre-industrial atmospheric CO2 with fixed vegetation (homogeneous shrubs everywhere) and dynamic vegetation. The results show that the simulations with dynamic vegetation are warmer in the global annual mean than the simulations with fixed shrubs by 0.9 °C at 2 × and 1.8 °C at 4 ×. Consequently, the warming when CO2 is doubled from 2 × to 4 × is 1 °C higher (in the global annual mean) with dynamic vegetation than with fixed shrubs. This corresponds to an increase in climate sensitivity of 26%. This difference in warming is enhanced at high latitudes, with temperatures increasing by over 50% in some regions of Antarctica. In the Arctic, ice–albedo feedbacks are responsible for the majority of this warming. On a global scale, energy balance analysis shows that the enhanced warming with dynamic vegetation is mainly associated with an increase in atmospheric water vapour but changes in clouds also contribute to the temperature increase. It is likely that changes in surface albedo due to changes in vegetation cover resulted in an initial warming which triggered these water vapour feedbacks. In conclusion, dynamic vegetation goes some way to resolving the discrepancy, but our modelled temperatures cannot reach the same warmth as the data suggest in the Arctic. This suggests that there are additional mechanisms, not included in this modelling framework, behind the polar warmth or that the proxies have been misinterpreted.

scholarly journals A model-data comparison for a multi-model ensemble of early Eocene atmosphere-ocean simulations: EoMIP

2012 ◽  
Vol 8 (2) ◽  
pp. 1229-1273 ◽  
Author(s):  
D. J. Lunt ◽  
T. Dunkley Jones ◽  
M. Heinemann ◽  
M. Huber ◽  
A. LeGrande ◽  
...  
Keyword(s):  
Lapse Rate ◽  
Early Eocene ◽  
Model Data ◽  
Data Comparison ◽  
Time Period ◽  
Modelling Studies ◽  
Balance Analysis ◽  
Co2 Level ◽  
Energy Balance Analysis ◽  
Model Variability

Abstract. The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project, and syntheses of early Eocene terrestrial and SST temperature data, we present a self-consistent inter-model and model-data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO2, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO2 level which would give optimal early Eocene model-data agreement, based on those models which have carried out simulations with more than one CO2 level, is in the range 2000 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO2 during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates, which could be used as a metric for weighting future climate predictions.

scholarly journals A model–data comparison for a multi-model ensemble of early Eocene atmosphere–ocean simulations: EoMIP

2012 ◽  
Vol 8 (5) ◽  
pp. 1717-1736 ◽  
Author(s):  
D. J. Lunt ◽  
T. Dunkley Jones ◽  
M. Heinemann ◽  
M. Huber ◽  
A. LeGrande ◽  
...  
Keyword(s):  
Lapse Rate ◽  
Early Eocene ◽  
Model Data ◽  
Data Comparison ◽  
Time Period ◽  
Modelling Studies ◽  
Balance Analysis ◽  
Co2 Level ◽  
Energy Balance Analysis ◽  
Model Variability

Abstract. The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project – and syntheses of early Eocene terrestrial and sea surface temperature data, we present a self-consistent inter-model and model–data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO2, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO2 level which would give optimal early Eocene model–data agreement, based on those models which have carried out simulations with more than one CO2 level, is in the range of 2500 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO2 and temperature during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates. If it is the case that a model which gives a good simulation of the Eocene will also give a good simulation of the future, then such an assessment could be used to produce metrics for weighting future climate predictions.

scholarly journals Upper tropospheric water vapour variability at high latitudes – Part 1: Influence of the annular modes

2015 ◽  
Vol 15 (16) ◽  
pp. 22291-22329 ◽  
Author(s):  
C. E. Sioris ◽  
J. Zou ◽  
D. A. Plummer ◽  
C. D. Boone ◽  
C. T. McElroy ◽  
...  
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
High Latitude ◽  
Lower Stratosphere ◽  
Southern Annular Mode ◽  
The Arctic ◽  
Boreal Winter ◽  
High Latitudes ◽  
Annular Mode ◽  
Annular Modes

Abstract. Seasonal and monthly zonal medians of water vapour in the upper troposphere and lower stratosphere (UTLS) are calculated for both Atmospheric Chemistry Experiment (ACE) instruments for the northern and southern high-latitude regions (60–90 and 60–90° S). Chosen for the purpose of observing high-latitude processes, the ACE orbit provides sampling of both regions in eight of 12 months of the year, with coverage in all seasons. The ACE water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS) are currently the only satellite instruments that can probe from the lower stratosphere down to the mid-troposphere to study the vertical profile of the response of UTLS water vapour to the annular modes. The Arctic oscillation (AO), also known as the northern annular mode (NAM), explains 64 % (r = −0.80) of the monthly variability in water vapour at northern high-latitudes observed by ACE-MAESTRO between 5 and 7 km using only winter months (January to March 2004–2013). Using a seasonal timestep and all seasons, 45 % of the variability is explained by the AO at 6.5 ± 0.5 km, similar to the 46 % value obtained for southern high latitudes at 7.5 ± 0.5 km explained by the Antarctic oscillation or southern annular mode (SAM). A large negative AO event in March 2013 produced the largest relative water vapour anomaly at 5.5 km (+70 %) over the ACE record. A similarly large event in the 2010 boreal winter, which was the largest negative AO event in the record (1950–2015), led to > 50 % increases in water vapour observed by MAESTRO and ACE-FTS at 7.5 km.

scholarly journals Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from middle to high latitudes

2020 ◽  
Vol 16 (4) ◽  
pp. 1387-1410 ◽  
Author(s):  
Christopher K. West ◽  
David R. Greenwood ◽  
Tammo Reichgelt ◽  
Alexander J. Lowe ◽  
Janelle M. Vachon ◽  
...  
Keyword(s):  
North America ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Early Eocene Climatic Optimum ◽  
Northern Half ◽  
Thermal Maximum ◽  
High Precipitation

Abstract. Early Eocene climates were globally warm, with ice-free conditions at both poles. Early Eocene polar landmasses supported extensive forest ecosystems of a primarily temperate biota but also with abundant thermophilic elements, such as crocodilians, and mesothermic taxodioid conifers and angiosperms. The globally warm early Eocene was punctuated by geologically brief hyperthermals such as the Paleocene–Eocene Thermal Maximum (PETM), culminating in the Early Eocene Climatic Optimum (EECO), during which the range of thermophilic plants such as palms extended into the Arctic. Climate models have struggled to reproduce early Eocene Arctic warm winters and high precipitation, with models invoking a variety of mechanisms, from atmospheric CO2 levels that are unsupported by proxy evidence to the role of an enhanced hydrological cycle, to reproduce winters that experienced no direct solar energy input yet remained wet and above freezing. Here, we provide new estimates of climate and compile existing paleobotanical proxy data for upland and lowland midlatitude sites in British Columbia, Canada, and northern Washington, USA, and from high-latitude lowland sites in Alaska and the Canadian Arctic to compare climatic regimes between the middle and high latitudes of the early Eocene – spanning the PETM to the EECO – in the northern half of North America. In addition, these data are used to reevaluate the latitudinal temperature gradient in North America during the early Eocene and to provide refined biome interpretations of these ancient forests based on climate and physiognomic data.

scholarly journals Paleobotanical proxies for early Eocene climates and ecosystems in northern North America from mid to high latitudes

2020 ◽  
Author(s):  
Christopher K. West ◽  
David R. Greenwood ◽  
Tammo Reichgelt ◽  
Alex J. Lowe ◽  
Janelle M. Vachon ◽  
...  
Keyword(s):  
North America ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
Early Eocene Climatic Optimum ◽  
Northern Half ◽  
Thermal Maximum ◽  
High Precipitation

Abstract. Early Eocene climates were globally warm, with ice-free conditions at both poles. Early Eocene polar landmasses supported extensive forest ecosystems of a primarily temperate biota, but also with abundant thermophilic elements such as crocodilians, and mesothermic taxodioid conifers and angiosperms. The globally warm early Eocene was punctuated by geologically brief hyperthermals such as the Paleocene-Eocene Thermal Maximum (PETM), culminating in the Early Eocene Climatic Optimum (EECO), during which the range of thermophilic plants such as palms extended into the Arctic. Climate models have struggled to reproduce early Eocene Arctic warm winters and high precipitation, with models invoking a variety of mechanisms, from atmospheric CO2 levels that are unsupported by proxy evidence, to the role of an enhanced hydrological cycle to reproduce winters that experienced no direct solar energy input yet remained wet and above freezing. Here, we provide new estimates of climate, and compile existing paleobotanical proxy data for upland and lowland mid-latitudes sites in British Columbia, Canada, and northern Washington, USA, and from high-latitude lowland sites in Alaska and the Canadian Arctic to compare climatic regimes between mid- and high latitudes of the early Eocene – spanning the PETM to the EECO – of the northern half of North America. In addition, these data are used to reevaluate the latitudinal temperate gradient in North America during the early Eocene, and to provide refined biome interpretations of these ancient forests based on climate and physiognomic data.

scholarly journals Tropical seaways played a more important role than high latitude seaways in Cenozoic cooling

2011 ◽  
Vol 7 (3) ◽  
pp. 801-813 ◽  
Author(s):  
Z. Zhang ◽  
K. H. Nisancioglu ◽  
F. Flatøy ◽  
M. Bentsen ◽  
I. Bethke ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Deep Water ◽  
Drake Passage ◽  
Central American ◽  
The Arctic ◽  
Early Eocene ◽  
High Latitudes ◽  
The West ◽  
Early Eocene Climatic Optimum ◽  
Tectonic Events

Abstract. Following the Early Eocene climatic optimum (EECO, ~55–50 Ma), climate deteriorated and gradually changed the earth from a greenhouse into an icehouse, with major cooling events at the Eocene-Oligocene boundary (∼34 Ma) and the Middle Miocene (∼15 Ma). It is believed that the opening of the Drake Passage had a marked impact on the cooling at the Eocene-Oligocene boundary. Based on an Early Eocene simulation, we study the sensitivity of climate and ocean circulation to tectonic events such as the closing of the West Siberian Seaway, the deepening of the Arctic-Atlantic Seaway, the opening of the Drake Passage, and the constriction of the Tethys and Central American seaways. The opening of the Drake Passage, together with the closing of the West Siberian Seaway and the deepening of the Arctic-Atlantic Seaway, weakened the Southern Ocean Deep Water (SODW) dominated ocean circulation and led to a weak cooling at high latitudes, thus contributing to the observed Early Cenozoic cooling. However, the later constriction of the Tethys and Central American Seaways is shown to give a strong cooling at southern high latitudes. This cooling was related to the transition of ocean circulation from a SODW-dominated mode to the modern-like ocean circulation dominated by North Atlantic Deep Water (NADW).

scholarly journals Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM

2009 ◽  
Vol 5 (4) ◽  
pp. 785-802 ◽  
Author(s):  
M. Heinemann ◽  
J. H. Jungclaus ◽  
J. Marotzke
Keyword(s):  
Surface Temperature ◽  
Water Vapour ◽  
High Latitude ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
High Latitudes ◽  
Radiative Effects ◽  
Proxy Data ◽  
Planetary Albedo

Abstract. We investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate atmospheric CO2 concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR), low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low in our PE simulation. To identify the mechanisms that cause the PE-PR surface temperature differences, we fit two simple energy balance models to the ECHAM5/MPI-OM results. We find that about 2/3 of the PE-PR global mean surface temperature difference are caused by a smaller clear sky emissivity due to higher atmospheric CO2 and water vapour concentrations in PE compared to PR; 1/3 is due to a smaller planetary albedo. The reduction of the pole-to-equator temperature gradient in PE compared to PR is due to (1) the large high-latitude effect of the higher CO2 and water vapour concentrations in PE compared to PR, (2) the lower Antarctic orography, (3) the smaller surface albedo at high latitudes, and (4) longwave cloud radiative effects. Our results support the hypothesis that local radiative effects rather than increased meridional heat transports were responsible for the "equable" PE climate.

scholarly journals Polar Amplification in CCSM4: Contributions from the Lapse Rate and Surface Albedo Feedbacks

2014 ◽  
Vol 27 (12) ◽  
pp. 4433-4450 ◽  
Author(s):  
Rune G. Graversen ◽  
Peter L. Langen ◽  
Thorsten Mauritsen
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Temperature Response ◽  
Global Scale ◽  
Lapse Rate ◽  
The Arctic ◽  
High Latitudes ◽  
Climate System Model ◽  
Polar Amplification ◽  
Rate Feedback

Abstract A vertically nonuniform warming of the troposphere yields a lapse rate feedback by altering the infrared irradiance to space relative to that of a vertically uniform tropospheric warming. The lapse rate feedback is negative at low latitudes, as a result of moist convective processes, and positive at high latitudes, due to stable stratification conditions that effectively trap warming near the surface. It is shown that this feedback pattern leads to polar amplification of the temperature response induced by a radiative forcing. The results are obtained by suppressing the lapse rate feedback in the Community Climate System Model, version 4 (CCSM4). The lapse rate feedback accounts for 15% of the Arctic amplification and 20% of the amplification in the Antarctic region. The fraction of the amplification that can be attributed to the surface albedo feedback, associated with melting of snow and ice, is 40% in the Arctic and 65% in Antarctica. It is further found that the surface albedo and lapse rate feedbacks interact considerably at high latitudes to the extent that they cannot be considered independent feedback mechanisms at the global scale.

scholarly journals Water vapour variability in the high-latitude upper troposphere – Part 2: Impact of volcanic emissions

2015 ◽  
Vol 15 (18) ◽  
pp. 25873-25905
Author(s):  
C. E. Sioris ◽  
J. Zou ◽  
C. T. McElroy ◽  
C. D. Boone ◽  
P. E. Sheese ◽  
...  
Keyword(s):  
Water Vapour ◽  
Atmospheric Chemistry ◽  
High Latitude ◽  
Volcanic Eruptions ◽  
Time Frame ◽  
The Arctic ◽  
High Latitudes ◽  
Volcanic Emissions ◽  
Upper Troposphere ◽  
The Impact

Abstract. The impact of volcanic eruptions on water vapour in the region of the high latitude tropopause is studied using deseasonalized time series based on observations by the Atmospheric Chemistry Experiment (ACE) water vapour sensors, namely MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and the Fourier Transform Spectrometer (ACE-FTS). The three eruptions with the greatest impact on the high latitude upper troposphere during the time frame of this satellite-based remote sensing mission are chosen. The Puyehue-Cordón Caulle volcanic eruption in June 2011 was the most explosive eruption in the past 24 years and resulted in an observed (50 ± 12) % increase in water vapour in the southern high-latitude upper troposphere in July 2011 that persisted into September 2011. A pair of Northern Hemisphere volcanoes, namely Eyjafjallajökull and Nabro, erupted in 2010 and 2011 respectively, increasing water vapour in the upper troposphere at northern high latitudes significantly for a period of ~ 3 months following each eruption. Both had a volcanic explosivity index of 4. Nabro led to a statistically significant increase of ~ 1 ppm in lower stratospheric (13.5–15.5 km) water vapour at northern high-latitudes (60–90° N) in September 2011, when the brunt of its plume arrived in the Arctic. These findings imply that steam emitted into the high-latitude, upper troposphere during volcanic eruptions must be taken into account to properly determine the magnitude of the trend in water vapour over the last decade.

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