scholarly journals Evaluating climate model performance with various parameter sets using observations over the last centuries

2010 ◽  
Vol 6 (2) ◽  
pp. 711-765 ◽  
Author(s):  
M. F. Loutre ◽  
A. Mouchet ◽  
T. Fichefet ◽  
H. Goosse ◽  
H. Goelzer ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Climate Projections ◽  
Freshwater Flux ◽  
The North ◽  
Climate Simulations ◽  
Wide Range ◽  
The North Atlantic

Abstract. Many sources of uncertainties limit the accuracy and precision of climate projections. Here, we focus on the parameter uncertainty, i.e. the imperfect knowledge of the values of many physical parameters in a climate model. We use LOVECLIM, a global three-dimensional Earth system model of intermediate complexity and vary several parameters within their range of uncertainty. Nine climatic parameter sets and three carbon cycle parameter sets are identified. They all yield present climate simulations coherent with observations and they cover a wide range of climate responses to doubled atmospheric CO2 concentration and freshwater flux in the North Atlantic sensitivity experiments. They also simulate a large range of atmospheric CO2 concentrations in response to prescribed emissions. Climate simulations of the last millennium are performed with the 27 combinations of these parameter sets. A special attention is given to the ability of LOVECLIM to reproduce the evolution of several climate variables over the last few decades, for which observations are available. The model response, even its ocean component, is strongly dominated by the model sensitivity to an increase in atmospheric CO2 concentration but much slightly by its sensitivity to freshwater flux in the North Atlantic. The whole set of parameter sets leads to a wide range of simulated climates. Although only some parameter sets yield simulations that reproduce the observed key variables of the climate system over the last decades, all of them could be used to characterise extreme climate projections.

scholarly journals Evaluating climate model performance with various parameter sets using observations over the recent past

2011 ◽  
Vol 7 (2) ◽  
pp. 511-526 ◽  
Author(s):  
M. F. Loutre ◽  
A. Mouchet ◽  
T. Fichefet ◽  
H. Goosse ◽  
H. Goelzer ◽  
...  
Keyword(s):  
Surface Temperature ◽  
North Atlantic ◽  
Climate Model ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Freshwater Flux ◽  
Recent Past ◽  
Atmospheric Co2 Concentration ◽  
The North ◽  
The North Atlantic

Abstract. Many sources of uncertainty limit the accuracy of climate projections. Among them, we focus here on the parameter uncertainty, i.e. the imperfect knowledge of the values of many physical parameters in a climate model. Therefore, we use LOVECLIM, a global three-dimensional Earth system model of intermediate complexity and vary several parameters within a range based on the expert judgement of model developers. Nine climatic parameter sets and three carbon cycle parameter sets are selected because they yield present-day climate simulations coherent with observations and they cover a wide range of climate responses to doubled atmospheric CO2 concentration and freshwater flux perturbation in the North Atlantic. Moreover, they also lead to a large range of atmospheric CO2 concentrations in response to prescribed emissions. Consequently, we have at our disposal 27 alternative versions of LOVECLIM (each corresponding to one parameter set) that provide very different responses to some climate forcings. The 27 model versions are then used to illustrate the range of responses provided over the recent past, to compare the time evolution of climate variables over the time interval for which they are available (the last few decades up to more than one century) and to identify the outliers and the "best" versions over that particular time span. For example, between 1979 and 2005, the simulated global annual mean surface temperature increase ranges from 0.24 °C to 0.64 °C, while the simulated increase in atmospheric CO2 concentration varies between 40 and 50 ppmv. Measurements over the same period indicate an increase in global annual mean surface temperature of 0.45 °C (Brohan et al., 2006) and an increase in atmospheric CO2 concentration of 44 ppmv (Enting et al., 1994; GLOBALVIEW-CO2, 2006). Only a few parameter sets yield simulations that reproduce the observed key variables of the climate system over the last decades. Furthermore, our results show that the model response, including its ocean component, is strongly influenced by the model sensitivity to an increase in atmospheric CO2 concentration but much less by its sensitivity to freshwater flux in the North Atlantic. They also highlight weaknesses of the model, in particular its large ocean heat uptake.

scholarly journals Impacts of the North Atlantic Warming Hole in Future Climate Projections: Mean Atmospheric Circulation and the North Atlantic Jet

2019 ◽  
Vol 32 (10) ◽  
pp. 2673-2689 ◽  
Author(s):  
Melissa Gervais ◽  
Jeffrey Shaman ◽  
Yochanan Kushnir
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Forced Response ◽  
Future Climate ◽  
Climate Projections ◽  
Transient Eddy ◽  
The North ◽  
Climate Simulations ◽  
The North Atlantic ◽  
The Impact

Abstract In future climate simulations there is a pronounced region of reduced warming in the subpolar gyre of the North Atlantic Ocean known as the North Atlantic warming hole (NAWH). This study investigates the impact of the North Atlantic warming hole on atmospheric circulation and midlatitude jets within the Community Earth System Model (CESM). A series of large-ensemble atmospheric model experiments with prescribed sea surface temperature (SST) and sea ice are conducted, in which the warming hole is either filled or deepened. Two mechanisms through which the NAWH impacts the atmosphere are identified: a linear response characterized by a shallow atmospheric cooling and increase in sea level pressure shifted slightly downstream of the SST changes, and a transient eddy forced response whereby the enhanced SST gradient produced by the NAWH leads to increased transient eddy activity that propagates vertically and enhances the midlatitude jet. The relative contributions of these two mechanisms and the details of the response are strongly dependent on the season, time period, and warming hole strength. Our results indicate that the NAWH plays an important role in midlatitude atmospheric circulation changes in CESM future climate simulations.

scholarly journals Millennial-scale variations of sedimentary oxygenation in the western subtropical North Pacific and its links to the North Atlantic climate

2019 ◽  
Author(s):  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Selvaraj Kandasamy ◽  
Xun Gong ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
North Pacific ◽  
Co2 Concentration ◽  
Meridional Overturning Circulation ◽  
Atmospheric Co2 ◽  
Intermediate Water ◽  
The North ◽  
The North Atlantic ◽  
Millennial Scale

Abstract. Lower glacial atmospheric CO2 concentrations have been attributed to carbon sequestration in deep oceans. However, potential roles of voluminous subtropical North Pacific in modulating atmospheric CO2 levels on millennial timescale are poorly constrained. Further, an increase in respired CO2 concentration in the glacial deep ocean due to biological pump generally is coeval with less oxygenation in the subsurface layer. This link thus offers a chance to visit oceanic ventilation and the coeval export productivity based on redox-controlled sedimentary geochemical parameters. Here we investigate a suite of sediment geochemical proxies to understand the sedimentary oxygenation variations in the subtropical North Pacific (core CSH1) over the last 50 thousand years (ka). Our results suggest that sedimentary oxygenation at mid-depths of the subtropical North Pacific intensifies during the episodes of late glacial (50–25 ka), Last Glacial Maximum (LGM) and also the interval after 8.5 ka, especially pronounced for the North Atlantic millennial-scale abrupt cold events of the Younger Dryas, Heinrich Stadial (HS) 1 and 2. On the other hand, oxygen-depleted seawater is found during the Bölling-Alleröd (B/A) and Preboreal. Our findings of enhanced sedimentary oxygenation in the subtropical North Pacific is aligned with intensified formation of North Pacific Intermediate Water (NPIW) during cold spells, while the ameliorated sedimentary oxygenation seems to be linked with the intensified Kuroshio Current since 8.5 ka. In our results, diminished sedimentary oxygenation during the B/A indicates an enhanced CO2 sequestration at mid-depth waters, along with slight increase in atmospheric CO2 concentration. Mechanistically, we speculate that these millennial-scale changes were linked to the strength of North Atlantic Deep Water, leading to intensification of NPIW formation and enhanced abyss flushing during deglacial cold and warm intervals, respectively. Enhanced formation of NPIW seem to be driven by the perturbation of sea ice formation and sea surface salinity oscillation in high latitude North Pacific through atmospheric and oceanic teleconnection. During the B/A, decreased sedimentary oxygenation likely resulted from an upward penetration of aged deep water into the intermediate-depth in the North Pacific, corresponding to a resumption of Atlantic Meridional Overturning Circulation.

scholarly journals Climate–Carbon Cycle Model Response to Freshwater Discharge into the North Atlantic

2007 ◽  
Vol 20 (24) ◽  
pp. 5962-5976 ◽  
Author(s):  
Atsushi Obata
Keyword(s):  
Carbon Cycle ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Younger Dryas ◽  
Co2 Concentration ◽  
Freshwater Discharge ◽  
Atmospheric Co2 ◽  
Carbon Cycle Model ◽  
The North ◽  
The North Atlantic

Abstract The response of a coupled climate–carbon cycle model to discharge of freshwater into the North Atlantic is investigated with regard to cold reversals caused by meltwater from northern continental ice sheets such as the Younger Dryas during the last deglaciation. The extreme case in which the North Atlantic thermohaline circulation ceases in several decades is discussed. In the preindustrial case, northern severe cooling is reproduced by the collapse of the Atlantic northward heat transport, and land carbon decreases because of a decrease in net primary production (NPP) by the cooling or precipitation decrease, resulting in a decrease in global air temperature and an increase in atmospheric carbon dioxide (CO2) concentration. The atmospheric CO2 increase by the land carbon decrease is consistent with a previous terrestrial vegetation model study and a minimum in ice core δ13CO2 during the Younger Dryas. The atmospheric CO2 increase in this model is less than 10 ppmv, consistent with the paleoclimatic records at the beginning of the Younger Dryas. This small increase results from the compensation between changes in CO2 sources and sinks of the land and ocean carbon cycles, such as the decrease in both NPP and soil respiration by the cooling. In the postindustrial case with fossil fuel CO2 emission, the same anomalies as the preindustrial case are found in the climate and the land carbon cycle in comparison with the control experiment without the freshwater discharge. After the termination of the freshwater discharge, the cold anomaly is globally reduced by the intense greenhouse effect of the increasing atmospheric CO2 on the order of 2000 ppmv, despite the weak thermohaline circulation in the North Atlantic. In contrast to the preindustrial case, the atmospheric CO2 concentration about 90 ppmv higher than the control experiment is caused mostly by the decrease in the ocean carbon uptake, which results from the decrease in the transport of anthropogenic carbon into the deep ocean by the collapse of the North Atlantic thermohaline circulation. The model results show the fact that there can be a case in the earth system where a decoupling can be seen between two environmental variables, air temperature and atmospheric CO2, that normally correlate with each other.

North Atlantic – European weather regimes in a changing climate: present and future

2020 ◽  
Author(s):  
Luise J. Fischer ◽  
Dominik Büeler ◽  
Christian M. Grams ◽  
Urs Beyerle ◽  
David N. Bresch ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Climate Model ◽  
Future Climate ◽  
Climate Projections ◽  
Climate Conditions ◽  
Weather Regimes ◽  
The North ◽  
Surface Weather ◽  
The North Atlantic

<p>We present findings from an analysis of weather regimes over the North Atlantic and Europe in present and future climate conditions. Weather regimes strongly influence the statistical distribution of surface weather variables. We use a recently developed, all-season North Atlantic - European weather regime classification with seven regimes. These regimes were originally identified in ERA-Interim reanalyses and, in this study, we investigate how they are represented in climate simulations using the CESM1 large ensemble for present-day and future (RCP8.5) climate conditions. With these regimes, the classification of the flow conditions in the considered region goes beyond the classical categorization according to the North Atlantic oscillation index; the weather regimes explicitly capture different flavors of strong zonal flows and the occurrence of blocking over Greenland, Scandinavia, and Central Europe, respectively. In ERA-Interim they explain 70% of the variability in geopotential height at 500 hPa year-round. Our analysis quantifies how well CESM1 represents the statistics of the weather regimes in present-day climate and how strongly their frequencies change in the future climate scenario. In addition, we identify statistical relationships between weather regimes and their resulting impacts on spatial patterns of surface variables such as precipitation. We compare those patterns and characteristics of the weather regimes identified in ERA-Interim to their characteristics in simulations of present and future climate conditions.</p><p>This analysis leads to insight into the representation of and changes in atmospheric circulation in one particular climate model, and, at the same time, it quantifies how well the climate model captures the observed link between surface weather and weather regimes. This approach contributes to improving our understanding of atmospheric circulation changes and their impact on a regional scale, and it may benefit the interpretation and communication of climate projections.</p>

scholarly journals The use of a flow field correction technique for alleviating the North Atlantic cold bias with application to the Kiel Climate Model

2015 ◽  
Vol 65 (8) ◽  
pp. 1079-1093 ◽  
Author(s):  
Annika Drews ◽  
Richard J. Greatbatch ◽  
Hui Ding ◽  
Mojib Latif ◽  
Wonsun Park
Keyword(s):  
Flow Field ◽  
North Atlantic ◽  
Climate Model ◽  
Cold Bias ◽  
The North ◽  
Correction Technique ◽  
The North Atlantic

Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

2021 ◽  
Author(s):  
Jing Sun ◽  
Mojib Latif ◽  
Wonsun Park
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Deep Convection ◽  
Meridional Overturning Circulation ◽  
Subpolar Gyre ◽  
Surface Salinity ◽  
The North ◽  
Ocean Coupling ◽  
Meridional Overturning ◽  
The North Atlantic

<p>There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA’s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.</p>

scholarly journals Modeling the climatic implications of the Guliya δ<sup>18</sup>O record during the past 130 ka

2012 ◽  
Vol 8 (3) ◽  
pp. 1885-1914
Author(s):  
D. Xiao ◽  
P. Zhao ◽  
Y. Wang ◽  
X. Zhou
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Late Summer ◽  
The Arctic ◽  
The Past ◽  
The North ◽  
Precession Cycle ◽  
The North Atlantic ◽  
Anomalous Pattern

Abstract. Using an intermediate-complexity UVic Earth System Climate Model (UVic Model), the geographical and seasonal implications and an indicative sense of the historical climate found in the δ18O record of the Guliya ice core (hereinafter, the Guliya δ18O) are investigated under time-dependent orbital forcing with an acceleration factor of 100 over the past 130 ka. The results reveal that the simulated late-summer (August–September) Guliya surface air temperature (SAT) reproduces the 23-ka precession and 43-ka obliquity cycles in the Guliya δ18O. Furthermore, the Guliya δ18O is significantly correlated with the SAT over the Northern Hemisphere (NH), which suggests the Guliya δ18O is an indicator of the late-summer SAT in the NH. Corresponding to the warm and cold phases of the precession cycle in the Guliya temperature, there are two anomalous patterns in the SAT and sea surface temperature (SST) fields. The first anomalous pattern shows an increase in the SAT (SST) toward the Arctic, possibly associated with the joint effect of the precession and obliquity cycles, and the second anomalous pattern shows an increase in the SAT (SST) toward the equator, possibly due to the influence of the precession cycle. Additionally, the summer (winter) Guliya and NH temperatures are higher (lower) in the warm phases of Guliya late-summer SAT than in the cold phases. Furthermore, the Guliya SAT is closely related to the North Atlantic SST, in which the Guliya precipitation may act as a "bridge" linking the Guliya SAT and the North Atlantic SST.

scholarly journals Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate

2018 ◽  
Vol 31 (12) ◽  
pp. 4791-4806 ◽  
Author(s):  
Qianzi Yang ◽  
Yingying Zhao ◽  
Qin Wen ◽  
Jie Yao ◽  
Haijun Yang
Keyword(s):  
Global Warming ◽  
North Atlantic ◽  
Coupled Model ◽  
Phase Changes ◽  
Box Model ◽  
Freshwater Flux ◽  
The North ◽  
Warming Climate ◽  
Transient Period ◽  
The North Atlantic

The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change.

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