scholarly journals Emulating IPCC AR4 atmosphere-ocean and carbon cycle models for projecting global-mean, hemispheric and land/ocean temperatures: MAGICC 6.0

2008 ◽  
Vol 8 (2) ◽  
pp. 6153-6272 ◽  
Author(s):  
M. Meinshausen ◽  
S. C. B. Raper ◽  
T. M. L. Wigley
Keyword(s):  
Carbon Cycle ◽  
General Circulation ◽  
Climate Model ◽  
Climate System ◽  
Ocean Heat Uptake ◽  
The Mean ◽  
Sres Scenarios ◽  
Ipcc Sres ◽  
Ipcc Ar4 ◽  
Global Mean

Abstract. Current scientific knowledge on the future response of the climate system to human-induced perturbations is comprehensively captured by various model intercomparison efforts. In the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), intercomparisons were organized for atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models, named "CMIP3" and "C4MIP", respectively. Despite their tremendous value for the scientific community and policy makers alike, there are some difficulties in interpreting the results. For example, key radiative forcings have not been considered or standardized in the majority of AOGCMs integrations and carbon cycle runs. Furthermore, the AOGCM analysis of plausible emission pathways was restricted to only three SRES scenarios. This study attempts to address these issues. We present an updated version of MAGICC, the simple carbon cycle-climate model used in past IPCC Assessment Reports with enhanced representation of time-varying climate sensitivities, carbon cycle feedbacks, aerosol forcings and ocean heat uptake characteristics. This new version of MAGICC (6.0) is successfully calibrated against the higher complexity AOGCM and carbon cycle models. Parameterizations of MAGICC 6.0 are provided. Previous MAGICC versions and emulations shown in IPCC AR4 (WG1, Fig. 10.26, page 803) yielded, in average, a 10% larger global-mean temperature increase over the 21st century compared to the AOGCMs. The reasons for this difference are discussed. The emulations presented here using MAGICC 6.0 match the mean AOGCM responses to within 2.2% for the SRES scenarios. This enhanced emulation skill is due to: the comparison on a "like-with-like" basis using AOGCM-specific subsets of forcings, a new calibration procedure, as well as the fact that the updated simple climate model can now successfully emulate some of the climate-state dependent effective climate sensitivities of AOGCMs. The mean diagnosed effective climate sensitivities of the AOGCMs is 2.88°C, about 0.33°C cooler than the reported slab ocean climate sensitivities. Finally, we examine the combined climate system and carbon cycle emulations for the complete range of IPCC SRES emission scenarios and some lower mitigation pathways.

scholarly journals Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 – Part 1: Model description and calibration

2011 ◽  
Vol 11 (4) ◽  
pp. 1417-1456 ◽  
Author(s):  
M. Meinshausen ◽  
S. C. B. Raper ◽  
T. M. L. Wigley
Keyword(s):  
Carbon Cycle ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Climate System ◽  
Model Description ◽  
Ocean Heat Uptake ◽  
The Mean ◽  
Sres Scenarios ◽  
Ipcc Sres

Abstract. Current scientific knowledge on the future response of the climate system to human-induced perturbations is comprehensively captured by various model intercomparison efforts. In the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), intercomparisons were organized for atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models, named "CMIP3" and "C4MIP", respectively. Despite their tremendous value for the scientific community and policy makers alike, there are some difficulties in interpreting the results. For example, radiative forcings were not standardized across the various AOGCM integrations and carbon cycle runs, and, in some models, key forcings were omitted. Furthermore, the AOGCM analysis of plausible emissions pathways was restricted to only three SRES scenarios. This study attempts to address these issues. We present an updated version of MAGICC, the simple carbon cycle-climate model used in past IPCC Assessment Reports with enhanced representation of time-varying climate sensitivities, carbon cycle feedbacks, aerosol forcings and ocean heat uptake characteristics. This new version, MAGICC6, is successfully calibrated against the higher complexity AOGCMs and carbon cycle models. Parameterizations of MAGICC6 are provided. The mean of the emulations presented here using MAGICC6 deviates from the mean AOGCM responses by only 2.2% on average for the SRES scenarios. This enhanced emulation skill in comparison to previous calibrations is primarily due to: making a "like-with-like comparison" using AOGCM-specific subsets of forcings; employing a new calibration procedure; as well as the fact that the updated simple climate model can now successfully emulate some of the climate-state dependent effective climate sensitivities of AOGCMs. The diagnosed effective climate sensitivity at the time of CO2 doubling for the AOGCMs is on average 2.88 °C, about 0.33 °C cooler than the mean of the reported slab ocean climate sensitivities. In the companion paper (Part 2) of this study, we examine the combined climate system and carbon cycle emulations for the complete range of IPCC SRES emissions scenarios and the new RCP pathways.

scholarly journals Emulating atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 – Part 2: Applications

2011 ◽  
Vol 11 (4) ◽  
pp. 1457-1471 ◽  
Author(s):  
M. Meinshausen ◽  
T. M. L. Wigley ◽  
S. C. B. Raper
Keyword(s):  
Carbon Cycle ◽  
21St Century ◽  
General Circulation ◽  
Climate Model ◽  
Coupled Model ◽  
General Circulation Models ◽  
Rcp Scenarios ◽  
Carbon Cycle Model ◽  
Uncertainty Range ◽  
Ipcc Ar4

Abstract. Intercomparisons of coupled atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models are important for galvanizing our current scientific knowledge to project future climate. Interpreting such intercomparisons faces major challenges, not least because different models have been forced with different sets of forcing agents. Here, we show how an emulation approach with MAGICC6 can address such problems. In a companion paper (Meinshausen et al., 2011a), we show how the lower complexity carbon cycle-climate model MAGICC6 can be calibrated to emulate, with considerable accuracy, globally aggregated characteristics of these more complex models. Building on that, we examine here the Coupled Model Intercomparison Project's Phase 3 results (CMIP3). If forcing agents missed by individual AOGCMs in CMIP3 are considered, this reduces ensemble average temperature change from pre-industrial times to 2100 under SRES A1B by 0.4 °C. Differences in the results from the 1980 to 1999 base period (as reported in IPCC AR4) to 2100 are negligible, however, although there are some differences in the trajectories over the 21st century. In a second part of this study, we consider the new RCP scenarios that are to be investigated under the forthcoming CMIP5 intercomparison for the IPCC Fifth Assessment Report. For the highest scenario, RCP8.5, relative to pre-industrial levels, we project a median warming of around 4.6 °C by 2100 and more than 7 °C by 2300. For the lowest RCP scenario, RCP3-PD, the corresponding warming is around 1.5 °C by 2100, decreasing to around 1.1 °C by 2300 based on our AOGCM and carbon cycle model emulations. Implied cumulative CO2 emissions over the 21st century for RCP8.5 and RCP3-PD are 1881 GtC (1697 to 2034 GtC, 80% uncertainty range) and 381 GtC (334 to 488 GtC), when prescribing CO2 concentrations and accounting for uncertainty in the carbon cycle. Lastly, we assess the reasons why a previous MAGICC version (4.2) used in IPCC AR4 gave roughly 10% larger warmings over the 21st century compared to the CMIP3 average. We find that forcing differences and the use of slightly too high climate sensitivities inferred from idealized high-forcing runs were the major reasons for this difference.

scholarly journals Palaeogeographic controls on climate and proxy interpretation

2016 ◽  
Vol 12 (5) ◽  
pp. 1181-1198 ◽  
Author(s):  
Daniel J. Lunt ◽  
Alex Farnsworth ◽  
Claire Loptson ◽  
Gavin L. Foster ◽  
Paul Markwick ◽  
...  
Keyword(s):  
Global Change ◽  
Carbon Cycle ◽  
Ocean Circulation ◽  
General Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Adjustment Factor ◽  
Climate Signal ◽  
Proxy Records ◽  
Global Mean

Abstract. During the period from approximately 150 to 35 million years ago, the Cretaceous–Paleocene–Eocene (CPE), the Earth was in a “greenhouse” state with little or no ice at either pole. It was also a period of considerable global change, from the warmest periods of the mid-Cretaceous, to the threshold of icehouse conditions at the end of the Eocene. However, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. Here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 General Circulation Model simulations covering this period, one simulation per stratigraphic stage. By maintaining atmospheric CO2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the CPE, and explore the underlying mechanisms. We find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. However, there are significant modelled variations on a regional scale. The stratigraphic stage–stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. We also find some control on global mean temperature from continental area and global mean orography. Our results have important implications for the interpretation of single-site palaeo proxy records. In particular, our results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. This “adjustment factor” is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. The adjustment factor is illustrated for seven key sites in the CPE, and applied to proxy data from Falkland Plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the CPE. Ultimately, this will enable isolation of the CO2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to CO2 changes during the CPE. Finally, regions where the adjustment factor is constant throughout the CPE could indicate places where future proxies could be targeted in order to reconstruct the purest CO2-induced temperature change, where the complicating contributions of other processes are minimised. Therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (21) ◽  
pp. 6505-6525 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

Modeling Tropical Cyclones in a Changing Climate

2016 ◽  
Author(s):  
Enrico Scoccimarro
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
General Circulation Model ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
Climate System ◽  
Ocean Dynamics ◽  
Small Scale ◽  
Computational Power

Tropical cyclones (TCs) in their most intense expression (hurricanes or typhoons) are the main natural hazards known to humankind. The impressive socioeconomic consequences for countries dealing with TCs make our ability to model these organized convective structures a key issue to better understanding their nature and their interaction with the climate system. The destructive effects of TCs are mainly caused by three factors: strong wind, storm surge, and extreme precipitation. These TC-induced effects contribute to the annual worldwide damage of the order of billions of dollars and a death toll of thousands of people. Together with the development of tools able to simulate TCs, an accurate estimate of the impact of global warming on TC activity is thus not only of academic interest but also has important implications from a societal and economic point of view. The aim of this article is to provide a description of the TC modeling implementations available to investigate present and future climate scenarios. The two main approaches to dynamically model TCs under a climate perspective are through hurricane models and climate models. Both classes of models evaluate the numerical equations governing the climate system. A hurricane model is an objective tool, designed to simulate the behavior of a tropical cyclone representing the detailed time evolution of the vortex. Considering the global scale, a climate model can be an atmosphere (or ocean)-only general circulation model (GCM) or a fully coupled general circulation model (CGCM). To improve the ability of a climate model in representing small-scale features, instead of a general circulation model, a regional model (RM) can be used: this approach makes it possible to increase the spatial resolution, reducing the extension of the domain considered. In order to be able to represent the tropical cyclone structure, a climate model needs a sufficiently high horizontal resolution (of the order of tens of kilometers) leading to the usage of a great deal of computational power. Both tools can be used to evaluate TC behavior under different climate conditions. The added value of a climate model is its ability to represent the interplay of TCs with the climate system, namely two-way relationships with both atmosphere and ocean dynamics and thermodynamics. In particular, CGCMs are able to take into account the well-known feedback between atmosphere and ocean components induced by TC activity and also the TC–related remote impacts on large-scale atmospheric circulation. The science surrounding TCs has developed in parallel with the increasing complexity of the mentioned tools, both in terms of progress in explaining the physical processes involved and the increased availability of computational power. Many climate research groups around the world, dealing with such numerical models, continuously provide data sets to the scientific community, feeding this branch of climate change science.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (3) ◽  
pp. 12115-12162 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall on both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affecting mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

scholarly journals Long-range memory in internal and forced dynamics of millennium-long climate model simulations

2014 ◽  
Vol 5 (2) ◽  
pp. 295-308 ◽  
Author(s):  
L. Østvand ◽  
T. Nilsen ◽  
K. Rypdal ◽  
D. Divine ◽  
M. Rypdal
Keyword(s):  
Long Range ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Climate System ◽  
Fluctuation Analysis ◽  
Scaling Exponent ◽  
External Forcing ◽  
Internal Dynamics ◽  
Temperature Records

Abstract. Northern Hemisphere (NH) temperature records from a palaeoclimate reconstruction and a number of millennium-long climate model experiments are investigated for long-range memory (LRM). The models are two Earth system models and two atmosphere–ocean general circulation models. The periodogram, detrended fluctuation analysis and wavelet variance analysis are applied to examine scaling properties and to estimate a scaling exponent of the temperature records. A simple linear model for the climate response to external forcing is also applied to the reconstruction and the forced climate model runs, and then compared to unforced control runs to extract the LRM generated by internal dynamics of the climate system. The climate models show strong persistent scaling with power spectral densities of the form S(f) ~ f −β with 0.8 < β < 1 on timescales from years to several centuries. This is somewhat stronger persistence than found in the reconstruction (β &amp;approx; 0.7). We find no indication that LRM found in these model runs is induced by external forcing, which suggests that LRM on sub-decadal to century time scales in NH mean temperatures is a property of the internal dynamics of the climate system. Reconstructed and instrumental sea surface temperature records for a local site, Reykjanes Ridge, are also studied, showing that strong persistence is found also for local ocean temperature.

scholarly journals The Bern Simple Climate Model (BernSCM) v1.0: an extensible and fully documented open source reimplementation of the Bern reduced form model for global carbon cycle-climate simulations

2017 ◽  
Author(s):  
Kuno Strassmann ◽  
Fortunat Joos
Keyword(s):  
Carbon Cycle ◽  
Open Source ◽  
Climate Model ◽  
Climate Modeling ◽  
Scientific Work ◽  
Climate System ◽  
Reduced Form ◽  
Impulse Response Functions ◽  
Emission Mitigation ◽  
Simple Climate Model

Abstract. The Bern Simple Climate Model (BernSCM v1.0) is a free open source reimplementation of a reduced form carbon cycle-climate model which has been used widely in previous scientific work and IPCC assessments. BernSCM represents the carbon cycle and climate system with a small set of equations for the heat and carbon budget, the parametrization of major nonlinearities, and the substitution of complex component systems with impulse response functions (IRF). The IRF approach allows cost-efficient yet accurate substitution of detailed parent models of climate system components with near linear behaviour. Illustrative simulations of scenarios from previous multi-model studies show that BernSCM is broadly representative of the range of the climate-carbon cycle response simulated by more complex and detailed models. Model code (in Fortran) was written from scratch with transparency and extensibility in mind, and is provided as open source. BernSCM makes scientifically sound carbon cycle-climate modeling available for many applications. Supporting up to decadal timesteps with high accuracy, it is suitable for studies with high computational load, and for coupling with, e.g., Integrated Assessment Models (IAM). Further applications include climate risk assessment in a business, public, or educational context, and the estimation of CO2 and climate benefits of emission mitigation options.

scholarly journals The Monash Simple Climate Model Experiments (MSCM-DB v1.0): An interactive database of mean climate, climate change and scenario simulations

2018 ◽  
Author(s):  
Dietmar Dommenget ◽  
Kerry Nice ◽  
Tobias Bayr ◽  
Dieter Kasang ◽  
Christian Stassen ◽  
...  
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Model Simulation ◽  
Co2 Concentration ◽  
General Circulation Models ◽  
Simple Climate Model ◽  
Model Simulations ◽  
Sensitivity Experiments ◽  
The Mean ◽  
Mean Climate

Abstract. This study introduces the Monash Simple Climate Model (MSCM) experiment database. The model simulations are based on the Globally Resolved Energy Balance (GREB) model. They provide a basis to study three different aspects of climate model simulations: (1) understanding the processes that control the mean climate, (2) the response of the climate to a doubling of the CO2 concentration, and (3) scenarios of external CO2 concentration and solar radiation forcings. A series of sensitivity experiments in which elements of the climate system are turned off in various combinations are used to address (1) and (2). This database currently provides more than 1,300 experiments and has an online web interface for fast analysis of the experiments and for open access to the data. We briefly outline the design of all experiments, give a discussion of some results, and put the findings into the context of previously published results from similar experiments. We briefly discuss the quality and limitations of the MSCM experiments and also give an outlook on possible further developments. The GREB model simulation of the mean climate processes is quite realistic, but does have uncertainties in the order of 20–30 %. The GREB model without flux corrections has a root mean square error in mean state of about 10 °C, which is larger than those of general circulation models (2 °C). However, the MSCM experiments show good agreement to previously published studies. Although GREB is a very simple model, it delivers good first-order estimates, is very fast, highly accessible, and can be used to quickly try many different sensitivity experiments or scenarios.

scholarly journals The impact of oceanic heat transport on the atmospheric circulation

2015 ◽  
Vol 6 (2) ◽  
pp. 591-615 ◽  
Author(s):  
M.-A. Knietzsch ◽  
A. Schröder ◽  
V. Lucarini ◽  
F. Lunkeit
Keyword(s):  
Entropy Production ◽  
Heat Transport ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Climate System ◽  
Hadley Cell ◽  
Near Surface ◽  
Oceanic Heat Transport ◽  
The Impact ◽  
Global Mean

Abstract. A general circulation model of intermediate complexity with an idealized Earth-like aquaplanet setup is used to study the impact of changes in the oceanic heat transport on the global atmospheric circulation. Focus is on the atmospheric mean meridional circulation and global thermodynamic properties. The atmosphere counterbalances to a large extent the imposed changes in the oceanic heat transport, but, nonetheless, significant modifications to the atmospheric general circulation are found. Increasing the strength of the oceanic heat transport up to 2.5 PW leads to an increase in the global mean near-surface temperature and to a decrease in its equator-to-pole gradient. For stronger transports, the gradient is reduced further, but the global mean remains approximately constant. This is linked to a cooling and a reversal of the temperature gradient in the tropics. Additionally, a stronger oceanic heat transport leads to a decline in the intensity and a poleward shift of the maxima of both the Hadley and Ferrel cells. Changes in zonal mean diabatic heating and friction impact the properties of the Hadley cell, while the behavior of the Ferrel cell is mostly controlled by friction. The efficiency of the climate machine, the intensity of the Lorenz energy cycle and the material entropy production of the system decline with increased oceanic heat transport. This suggests that the climate system becomes less efficient and turns into a state of reduced entropy production as the enhanced oceanic transport performs a stronger large-scale mixing between geophysical fluids with different temperatures, thus reducing the available energy in the climate system and bringing it closer to a state of thermal equilibrium.

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