We investigate the relationship between the Last Glacial Maximum (LGM) and climate sensitivity across the PMIP2 multi‐model ensemble of GCMs, and find a correlation between tropical temperature and ...climate sensitivity which is statistically significant and physically plausible. We use this relationship, together with the LGM temperature reconstruction of Annan and Hargreaves (2012), to generate estimates for the equilibrium climate sensitivity. We estimate the equilibrium climate sensitivity to be about 2.5°C with a high probability of being under 4°C, though these results are subject to several important caveats. The forthcoming PMIP3/CMIP5 models were not considered in this analysis, as very few LGM simulations are currently available from these models. We propose that these models will provide a useful validation of the correlation presented here.
Key Points
Climate sensitivity is estimated using data and models from the LGM
The best estimate is about 2.5C with a high probability of being under 4C
Consistent results are obtained with Bayesian and Frequentist methods
Paleoclimate experiments using contemporary climate models are an effective measure to evaluate climate models. In recent years, Earth system models (ESMs) were developed to investigate carbon cycle ...climate feedbacks, as well as to project the future climate. Paleoclimate events can be suitable benchmarks to evaluate ESMs. The variation in aerosols associated with the volcanic eruptions provide a clear signal in forcing, which can be a good test to check the response of a climate model to the radiation changes. The variations in atmospheric CO2 level or changes in ice sheet extent can be used for evaluation as well. Here we present implementations of the paleoclimate experiments proposed by the Coupled Model Intercomparison Project phase 5/Paleoclimate Modelling Intercomparison Project phase 3 (CMIP5/PMIP3) using MIROC-ESM, an ESM based on the global climate model MIROC (Model for Interdisciplinary Research on Climate). In this paper, experimental settings and spin-up procedures of the mid-Holocene, the Last Glacial Maximum, and the Last Millennium experiments are explained. The first two experiments are time slice experiments and the last one is a transient experiment. The complexity of the model requires various steps to correctly configure the experiments. Several basic outputs are also shown.
Both historical and idealized climate model experiments are performed with a variety of Earth system models of intermediate complexity (EMICs) as part of a community contribution to the ...Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes appear to be slightly underestimated. It is possible that recent modelled climate trends or climate–carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2 × and 4 × CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate–carbon feedbacks. The values from EMICs generally fall within the range given by general circulation models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows a non-linear interaction between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from palaeoclimate reconstructions. This in turn could be a result of unforced variability within the climate system, uncertainty in the reconstructions of temperature and CO2, errors in the reconstructions of forcing used to drive the models, or the incomplete representation of certain processes within the models. Given the forcing datasets used in this study, the models calculate significant land-use emissions over the pre-industrial period. This implies that land-use emissions might need to be taken into account, when making estimates of climate–carbon feedbacks from palaeoclimate reconstructions.
We calculate the
7Be production rate in the atmosphere assuming the galactic cosmic ray and solar proton spectra in 2002–2004. The global average production rate is 0.043
7Be/cm
2
s that is in ...agreement with the previous ones within a factor of ∼2. Although intense protons associated with an extraordinary large solar event (X17/4B) on Oct. 28, 2003 produce
7Be in the polar region, the effect of solar protons is not significant because the solar proton spectrum is soft. The latitudinal production rate at geomagnetic latitude 20–30° (Japan) is 0.023
7Be/cm
2
s, indicating ∼1% of cosmic-ray produced
7Be contributes to the surface
7Be radioactivity. The temporal variations in the surface
7Be radioactivity in Tokyo exhibit the enhancements in spring and autumn. We discuss the possibility of the stratospheric–tropospheric air mass exchange caused by a periodic passage of a pair of a traveling anticyclone and extratropical cyclone in spring and autumn.
7Be is a cosmogenic radionucleide (half life 53.3 days) produced by galactic cosmic rays and solar energetic particles in the upper atmosphere and is a potentially useful tracer of the short-term ...atmospheric air mass motion. We have measured the surface
7Be concentration in Tokyo (35N, 139E) since 2002 with a high-volume air sampler. The present data of surface Be-7 concentrations exhibit the enhancements in spring and autumn and the seasonal enhancements are not associated with scavenging by precipitation. In order to explain the measured enhancements, we propose the possibility of the downward and upward atmospheric flows in the troposphere caused by a pair of traveling anticyclone and extratropical cyclone that passes over Japan in spring and autumn with a period of a few days.
The resumption process of the North Atlantic meridional overturning circulation (MOC) is investigated in a series of freshwater hosing experiments using a comprehensive coupled climate model. Four ...different freshwater perturbations are applied to the North Atlantic between 50°N and 70°N leading to a substantial weakening of MOC and an expansion of winter sea ice cover over the Greenland–Iceland–Norwegian (GIN) Seas. Deactivating the freshwater forcing leads to a two-phase recovery of the MOC. The first phase is a slow basin-wide advection process whereas the second phase is an abrupt, decadal-scale transition, located in the North Atlantic. The slow basin-wide advection process to an intermediate state of the MOC is characterized by a restart of the deep water production in the area of the subpolar gyre and the Irminger Basin. However, the ice cover over the GIN Seas remains, whereas the surface density gradually increases in the GIN Seas on a century time scale. The length of this intermediate state depends on the strength of freshwater perturbation, which determines the magnitude of the meridional density gradient in the North Atlantic. The second transition phase is triggered by a model-specific density threshold reached in the GIN Seas. When passed, the MOC abruptly intensifies by ∼60% within 60–80 years. The analysis shows that this abrupt intensification only depends on surface salinity in the GIN Seas. The model results reveal that the simulated sea ice retreat in the GIN Seas and a rapid increase of the Greenland air temperature of the second phase of the resumption of the MOC are similar in amplitude to temperature proxies observed during Dansgaard–Oeschger events of the last ice age.
Extreme midlatitude cyclone characteristics, precipitation, wind speed events, their inter-relationships, and the connection to large-scale atmospheric patterns are investigated in simulations of a ...prolonged cold period, known as the Maunder Minimum from 1640 to 1715 and compared with today. An ensemble of six simulations for the Maunder Minimum as well as a control simulation for perpetual 1990 conditions are carried out with a coupled atmosphere-ocean general circulation model, i.e., the Climate Community System Model (CCSM). The comparison of the simulations shows that in a climate state colder than today the occurrence of cyclones, the extreme events of precipitation and wind speed shift southward in all seasons in the North Atlantic and the North Pacific. The extremes of cyclone intensity increases significantly in winter in almost all regions, which is related to a stronger meridional temperature gradient and an increase in lower tropospheric baroclinicity. Extremes of cyclone intensity in subregions of the North Atlantic are related to extremes in precipitation and in wind speed during winter. Moreover, extremes of cyclone intensity are also connected to distinct large-scale atmospheric patterns for the different subregions, but these relationships vanish during summer. Analyzing the mean 1,000 hPa geopotential height change of the Maunder Minimum simulations compared with the control simulation, we find a similar pattern as the correlation pattern with the cyclone intensity index of the southern Europe cyclones. This illustrates that changes in the atmospheric high-frequency, i.e., the simulated southward shift of cyclones in the North Atlantic and the related increase of extreme precipitation and wind speed in particular in the Mediterranean in winter, are associated with large-scale atmospheric circulation changes.
It is now widely recognized that climate change affects multiple sectors in virtually every part of the world. Impacts on one sector may influence other sectors, including seemingly remote ones, ...which we call “interconnections of climate risks.” While a substantial number of climate risks are identified in the Intergovernmental Panel on Climate Change Fifth Assessment Report, there have been few attempts to explore the interconnections between them in a comprehensive way. To fill this gap, we developed a methodology for visualizing climate risks and their interconnections based on a literature survey. Our visualizations highlight the need to address climate risk interconnections in impact and vulnerability studies. Our risk maps and flowcharts show how changes in climate impact natural and socioeconomic systems, ultimately affecting human security, health, and well‐being. We tested our visualization approach with potential users and identified likely benefits and issues. Our methodology can be used as a communication tool to inform decision makers, stakeholders, and the general public of the cascading risks that can be triggered by climate change.
Plain Language Summary
The paper demonstrates in a most holistic manner how climate change can generate various risks and how they are actually interconnected. Based on a literature survey using the Intergovernmental Panel on Climate Change Fifth Assessment Report, we identified 91 climate risks and 253 causal relationships among them and graphically drew such interconnected risks. We found that changes in the climate system impact the natural and socioeconomic system, influencing ultimately human security, health, and well‐being. This indicates that climate change can trigger a cascade of impacts across sectors. Our findings point to the need to address the climate risk interconnections in impact and vulnerability studies. We tested our visualization approach with potential users and identified likely benefits and issues. The implications of our study go beyond science. Our study is useful to inform stakeholders of a broad yet fresh perspective of climate risks that have not been presented before.
Key Points
The paper developed a methodology for visualizing how climate change can generate various risks and how they can be interconnected
We identified 91 climate risks and 253 causal relationships among them based on a literature survey and graphically presented the interconnected risks
We found that changes in the climate system impact natural and socioeconomic systems, ultimately influencing human security, health, and well‐being
The decadal trend behavior of the Northern Hemisphere atmospheric circulation is investigated utilizing long-term simulations with different state-of-the-art coupled general circulation models (GCMs) ...for present-day climate conditions (1990), reconstructions of the past 500 yr, and observations. The multimodel simulations show that strong positive winter North Atlantic Oscillation (NAO) trends are connected with the underlying sea surface temperature (SST) and exhibit an SST tripole trend pattern and a northward shift of the storm-track tail. Strong negative winter trends of the Aleutian low are associated with SST changes in the El Niño–Southern Oscillation (ENSO) region and a westward shift of the storm track in the North Pacific. The observed simultaneous appearance of strong positive NAO and negative Aleutian low trends is very unlikely to occur by chance in the unforced simulations and reconstructions. The positive winter NAO trend of the last 50 yr is not statistically different from the level of internal atmosphere–ocean variability. The unforced simulations also show a strong link between positive SST trends in the ENSO region and negative Aleutian low trends. With much larger observed SST trends in the ENSO region, this suggests that the observed negative Aleutian low trend is possibly influenced by external forcing, for example, global warming, volcanism, and/or solar activity change.
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