ORCID Profile
0000-0002-5507-9209
Current Organisation
Stockholm University
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Publisher: Copernicus GmbH
Date: 13-06-2018
Abstract: Abstract. The Eocene–Oligocene transition (EOT), which took place approximately 34 Ma ago, is an interval of great interest in Earth's climate history, due to the inception of the Antarctic ice sheet and major global cooling. Climate simulations of the transition are needed to help interpret proxy data, test mechanistic hypotheses for the transition and determine the climate sensitivity at the time. However, model studies of the EOT thus far typically employ control states designed for a different time period, or ocean resolution on the order of 3∘. Here we developed a new higher resolution palaeoclimate model configuration based on the GFDL CM2.1 climate model adapted to a late Eocene (38 Ma) palaeogeography reconstruction. The ocean and atmosphere horizontal resolutions are 1∘ × 1.5∘ and 3∘ × 3.75∘ respectively. This represents a significant step forward in resolving the ocean geography, gateways and circulation in a coupled climate model of this period. We run the model under three different levels of atmospheric CO2: 400, 800 and 1600 ppm. The model exhibits relatively high sensitivity to CO2 compared with other recent model studies, and thus can capture the expected Eocene high latitude warmth within observed estimates of atmospheric CO2. However, the model does not capture the low meridional temperature gradient seen in proxies. Equatorial sea surface temperatures are too high in the model (30–37 ∘C) compared with observations (max 32 ∘C), although observations are lacking in the warmest regions of the western Pacific. The model exhibits bipolar sinking in the North Pacific and Southern Ocean, which persists under all levels of CO2. North Atlantic surface salinities are too fresh to permit sinking (25–30 psu), due to surface transport from the very fresh Arctic (∼ 20 psu), where surface salinities approximately agree with Eocene proxy estimates. North Atlantic salinity increases by 1–2 psu when CO2 is halved, and similarly freshens when CO2 is doubled, due to changes in the hydrological cycle.
Publisher: Copernicus GmbH
Date: 23-02-2017
Abstract: Abstract. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼ 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 × CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
Publisher: Springer Science and Business Media LLC
Date: 22-08-2019
DOI: 10.1038/S41467-019-11828-Z
Abstract: The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-7493
Abstract: & & & strong& The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures.& /strong& & &
Publisher: Frontiers Media SA
Date: 07-05-2019
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-12-2019
Abstract: A rapid rise in CO 2 has made evergreen trees more waterwise than deciduous trees, especially in cooler parts of the world.
Publisher: Copernicus GmbH
Date: 09-01-2018
DOI: 10.5194/CP-2017-161
Abstract: Abstract. The Eocene–Oligocene Transition (EOT), approximately 34 Ma ago, is an interval of great interest in Earth's climate history, due to the inception of the Antarctic ice sheet and major global cooling at the time. Climate simulations of the transition are needed to help us interpret proxy data, test mechanistic hypotheses for the transition, and determine the climate sensitivity at the time. However, model studies of the EOT thus far typically employ control states designed for a different time period, or ocean resolution on the order of 3 degrees. Here we developed a new higher resolution paleoclimate model configuration based on the GFDL CM2.1 climate model adapted to a late Eocene (38 Ma) paleogeography reconstruction. We employ an ocean resolution of 1 × 1.5 degrees, and an atmosphere resolution of 3 × 3.75 degrees. This represents a significant step forward in resolving the ocean geography, gateways and circulation in a coupled climate model of this period. We simulate the model under 3 different levels of CO2 400, 800 and 1600 ppm. The model exhibits relatively high sensitivity to CO2 compared with other recent model studies, and thus can capture the expected Eocene high latitude warmth within observed estimates of atmospheric CO2. However, the model does not capture the low meridional temperature gradient seen in proxies. Equatorial sea surface temperatures are too high in the model (30–37 degrees C) compared with observations (max 32 degrees C), though observations are lacking in the warmest regions of the western Pacific. The model exhibits robust bipolar sinking in the North Pacific and Southern Ocean, which persists under all levels of CO2. North Atlantic salinities are too fresh to permit sinking (25–30 psu), due to surface transport from the very fresh Arctic (~ 20 psu), whose salinities approximately agree with Eocene proxy estimates. North Atlantic salinity increases by 1–2 psu when CO2 is halved, and similarly freshens when CO2 is doubled, due to changes in the hydrological cycle.
Publisher: American Meteorological Society
Date: 04-2013
DOI: 10.1175/BAMS-D-11-00154.1
Abstract: The variability of results from different automated methods of detection and tracking of extratropical cyclones is assessed in order to identify uncertainties related to the choice of method. Fifteen international teams applied their own algorithms to the same dataset—the period 1989–2009 of interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERAInterim) data. This experiment is part of the community project Intercomparison of Mid Latitude Storm Diagnostics (IMILAST see www.proclim.ch/imilast/index.html). The spread of results for cyclone frequency, intensity, life cycle, and track location is presented to illustrate the impact of using different methods. Globally, methods agree well for geographical distribution in large oceanic regions, interannual variability of cyclone numbers, geographical patterns of strong trends, and distribution shape for many life cycle characteristics. In contrast, the largest disparities exist for the total numbers of cyclones, the detection of weak cyclones, and distribution in some densely populated regions. Consistency between methods is better for strong cyclones than for shallow ones. Two case studies of relatively large, intense cyclones reveal that the identification of the most intense part of the life cycle of these events is robust between methods, but considerable differences exist during the development and the dissolution phases.
No related grants have been discovered for Rodrigo Caballero.