Julia Catherine Hargreaves

BlueSkiesResearch.org.uk

The concept of independence has been frequently mentioned in climate science research, but has rarely been defined and discussed in a theoretically robust and quantifiable manner. In this paper we argue that any discussion must start from a clear and unambiguous definition of what independence means and how it can be determined. We introduce an app...

The concept of independence has been frequently raised in climate science, but has rarely been defined and discussed in a theoretically robust and quantifiable manner. Improved understanding of this topic is critical to better understanding of climate change. In this paper, we introduce a unifying approach based on the statistical definition of ind...

The mid-Pliocene Warm Period (mPWP) is the most recent interval in which atmospheric carbon dioxide was substantially higher than in modern pre-industrial times. It is, therefore, a potentially valuable target for testing the ability of climate models to simulate climates warmer than the pre-industrial state. The recent Pliocene Model Intercomparis...

The mid-PlioceneWarm Period (mPWP) is the most recent interval in which atmospheric carbon dioxide was substantially higher than in modern pre-industrial times. It is, therefore, a potentially valuable target for testing the ability of climate models to simulate climates warmer than the pre-industrial state. The recent Pliocene model inter-comparis...

Structural differences among models account for much of the uncertainty in projected climate changes, at least until the mid-twenty-first century. Recent observations encompass too limited a range of climate variability to provide a robust test of the ability to simulate climate changes. Past climate changes provide a unique opportunity for out-of-...

What are the predictions of climate models, should we believe them, and are they falsifiable? Probably the most iconic and influential result arising from climate models is the prediction that, dependent on the rate of increase of CO 2 emissions, global and annual mean temperature will rise by around 2–4°C over the 21st century. We argue that this...

We present a selection of methodologies for using the palaeo-climate model component of the Coupled Model Intercomparison Project (Phase 5) (CMIP5) to attempt to constrain future climate projections using the same models. The constraints arise from measures of skill in hindcasting palaeo-climate changes from the present over three periods: the Last...

We investigate the performance of the newest generation multi-model ensemble (MME) from the Cou-pled Model Intercomparison Project (CMIP5). We com-pare the ensemble to the previous generation models (CMIP3) as well as several single model ensembles (SMEs), which are constructed by varying components of single models. These SMEs range from ensembles...

Climate change research in Japan has shifted focus significantly in the past 2 years, with a greater emphasis on risks, extreme events, and abrupt changes. Two new national government-funded 5-year projects, Integrated Climate Assessment—Risks, Uncertainty and Society (ICA-RUS) and Program for Risk Information on Climate Change (SOUSEI) will focus...

We examined the flows of nitrogen in two batch incubations of plankton assemblages under controlled conditions, using mesopelagic seawater from different depths. Observations included concentrations of nutrients, organic matter (particulate and dissolved) and plankton (biomass by species). Because nitrogen flows were not observed directly (as is ge...

Comparison of model outputs with observations of the climate system forms an essential component of model assessment and is crucial for building our confidence in model predictions. Methods for undertaking this comparison are not always clearly justified and understood. Here we show that the popular approach of comparing the ensemble spread in clim...

During the Last Interglacial period (~ 130–115 thousand years ago) the Arctic climate was warmer than today, and global mean sea level was probably more than 6.6 m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps)....

Paleoclimate simulations provide us with an opportunity to critically confront and evaluate the performance of climate models in simulating the response of the climate system to changes in radiative forcing and other boundary conditions. Hargreaves et al. (2011) analysed the reliability of the Paleoclimate Modelling Intercomparison Project, PMIP2 m...

Some recent compilations of proxy data both on land and ocean (MARGO Project Members, 2009; Bartlein et al., 2011; Shakun et al., 2012), have provided a new opportunity for an improved assessment of the overall climatic state of the Last Glacial Maximum. In this paper, we combine these proxy data with the ensemble of structurally diverse state of t...

We present a description of the theoretical framework and "best practice" for using the paleo-climate model component of the Coupled Model Intercomparison Project (Phase 5) (CMIP5) to constrain future projections of climate using the same models. The constraints arise from measures of skill in hindcasting paleo-climate changes from the present over...

In this study, we constructed a perturbed physics ensemble (PPE) for the MIROC5 coupled atmosphere-ocean general circulation model (CGCM) to investigate the parametric uncertainty of climate sensitivity (CS). Previous studies of PPEs have mainly used the atmosphere-slab ocean models. A few PPE studies using a CGCM applied flux corrections, because...

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 reconstruct...

Some recent compilations of proxy data both on land and ocean (MARGO Project Members, 2009; Bartlein et al., 2011; Shakun et al., 2012), have provided a new opportunity for an improved assessment of the overall climatic state of the Last Glacial Maximum. In this paper, we combine these proxy data with the ensemble of structurally diverse state of t...

The observed dramatic decrease in September sea ice extent (SIE) has been widely discussed in the scientific literature. Though there is qualitative agreement between observations and ensemble members of the Third Coupled Model Intercomparison Project (CMIP3), it is concerning that the observed trend (1979–2010) is not captured by any ensemble memb...

This study proposes a systematic approach to investigate cloud-radiative feedbacks to climate change induced by an increase of CO2 concentrations in global climate models (GCMs). Based on two versions of the Model for Interdisciplinary Research on Climate (MIROC), which have opposite signs for cloud–shortwave feedback (ΔSWcld) and hence different e...

Paleoclimate simulations provide us with an opportunity to critically confront and evaluate the performance of climate models in simulating the response of the climate system to changes in radiative forcing and other boundary conditions. Hargreaves et al. (2011) analysed the reliability of the PMIP2 model ensemble with respect to the MARGO sea surf...

We investigate the identifiability of the climate by limited proxy data. We test a data assimilation approach through perfect model pseudoproxy experiments, using a simple likelihood-based weighting based on the particle filtering process. Our experimental set-up enables us to create a massive 10 000-member ensemble at modest computational cost, th...

The Last Interglaciation (~ 130-115 thousand years ago) was a time when the Arctic climate was warmer than today (Anderson et al., 2006; Kaspar et al., 2005) and sea-level extremely likely at least 6 m higher (Kopp et al., 2009). However, there is large uncertainty in the relative contributions to this sea-level rise from the Greenland and Antarcti...

The use of information from paleoclimates as a means of assessing the performance of global climate models has long been considered an important motivation of paleoclimate research, but this tenet has only recently become widely accepted in the mainstream climate modelling community, with several standard paleoclimate simulation experiments being,...

The world climate research centres are currently running Earth System Models (ESMs) forced by Representative Concentration Pathways (RCP) scenarios. Based on these future pathways in atmospheric greenhouse gas concentrations, the emphasis has been mainly on estimating the associated levels of global warming that might be expected. There is also the...

The equilibrium climate response to anthropogenic forcing has long been one of the dominant, and therefore most intensively studied, uncertainties in predicting future climate change. As a result, many probabilistic estimates of the climate sensitivity (S) have been presented. Despite improved models and additional observations, however, there has...

Several collations of proxy data dating from the Last Glacial Maximum have been published, but they have rarely if ever been synthesised into a true global field or mean. While various arguments have previously been presented to the effect that the LGM mean temperature change was around -5C relative to pre-industrial, a recent analysis of Schmittne...

We discuss the assessment of model ensembles such as that arising from the CMIP3 coordinated multi-model experiments. An important aspect of this is not merely the closeness of the models to observations in absolute terms but also the reliability of the ensemble spread as an indication of uncertainty. In this context, it has been widely argued that...

The reproduction of the change of Atlantic Meridional Overturning Circulation (AMOC) by Coupled Atmosphere Ocean General Circulation Models (AOGCMs) is crucial for the future climate projection since it is important for both the global heat transport and the carbon cycle. Information from the paleo-proxy data shows a distinct change of the glacial...

In the present study we investigate the performance of climate models which contributed to the past 3 Intergovernmental Panel for Climate Change (IPCC) assessment reports for the Gangetic West Bengal region of east India (6 degrees x 6 degrees). Analysing present-day seasonal rainfall and temperature over the domain, we compare the results of the m...

In the climate-carbon cycle system, the terrestrial ecosystem feedback is significant. In studies on feedback analysis, the ecosystem feedback is divided into the sensitivity of carbon storage to atmospheric CO2 concentra- tion (bL), and temperature change (gL). Although ecosystems include many nonlinear processes, the scenario- and time-dependency...

We investigate the identifiability of the climate by limited proxy data. We test a data assimilation approach through perfect model pseudoproxy experiments, using a simple likelihood-based weighting based on the particle filtering process. Our experimental set-up enables us to create a massive 10 000-member ensemble at modest computational cost, th...

One of the most important issues in cloud modeling and observation is to understand and validate cloud responses to global warming. Our group have created various kinds of climate model ensembles from different versions of Model for Interdisciplinary Research on Climate (MIROC), and used them as well as the multi-model ensemble (MME) of the Coupled...

Following the recommendation by CMIP5, some world climate centers are running experiments with Representative Concentration Pathways (RCP) concentration scenario, and will present allowable carbon emission in the future. As allowable carbon emission is determined by combination of climate response and feedback of ecosystem, there should be signific...

Multi-model investigations with GCMs indicate that about half of the observed dramatic decline in sea ice can be accounted for by greenhouse gas (GHG) forcing. This suggests that climate variability plays a significant role in the observed decline in summer sea ice extent (SIE). For example, there is strong evidence that both the Arctic Oscillation...

The interpretation and analysis of output from multi-model climate modelling experiments such as CMIP5 is an important topic of research, but the properties and behaviour of the resulting "ensembles of opportunity" are not well understood. The result is that a wide range of sometimes inconsistent approaches have been used. Here we discuss some theo...

Reconstructions of the past millennium can help us to understand recent and future climate change, by placing the recent anthropogenically-forced changes in the context of natural variability. Proxy data prior to the instrumental era are, however, extremely limited, which raises the question of how well we can truly hope to understand the past. Unt...

The principal obstacle to assessing the reliability of projections from the multi-model ensembles is the long term nature of the forecast, which means that it is not possible to regularly confront the forecast system with new observational data. Thus, while encouraging results have been obtained assessing the CMIP3 ensemble on the global scale with...

For probabilistic climate predictions, we need to create ensembles of model simulations and evaluate their reliability. In some studies, it has been assumed that the truth should be close to the center of ensembles ("truth-centered paradigm"). On the other hand, an alternative paradigm is to consider the truth as being drawn from the distribution s...

Climate sensitivity is one of the most important metrics for future climate projections. In previous studies the climate of the last glacial maximum has been used to constrain the range of climate sensitivity, and similarities and differences of temperature response to the forcing of the last glacial maximum and to idealized future forcing have bee...

Comparison of model outputs with observations of the climate system forms an essential component of model assessment and is crucial for building our confidence in model predictions. Methods for undertaking this comparison are not always clearly justified and understood. Here we show that the popular approach of comparing the ensemble spread to a so...

In this study, we used two novel methods to estimate urban contamination in the Japanese temperature record of the last century. First, we tested different criteria for choosing the rural stations, and found little sensitivity to the method, though the presence of a decreasing local population trend appeared to be a useful indicator. Second, we inv...

We investigate the consistency of various ensembles of model simulations with the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) sea surface temperature data synthesis. We discover that while two multi-model ensembles, created through the Paleoclimate Model Intercomparison Projects (PMIP and PMIP2), pass our simple...

The performance of several state-of-the-art cli-mate model ensembles, including two multi-model ensem-bles (MMEs) and four structurally different (perturbed parameter) single model ensembles (SMEs), are investi-gated for the first time using the rank histogram approach. In this method, the reliability of a model ensemble is evaluated from the point...

The Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel ensemble has been widely utilized for climate research and prediction, but the properties and behavior of the ensemble are not yet fully understood. Here, some investigations are undertaken into various aspects of the ensemble's behavior, in particular focusing on the performance...

We investigate the consistency of various ensembles of climate model simulations with the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) sea surface temperature data synthesis. We discover that while two multi-model ensembles, created through the Paleoclimate Model Intercomparison Projects (PMIP and PMIP2), pass our...

Henriksson et al. (2010), hereafter HALTL10, criticize Annan and Hargreaves (2006a) (AH06) primarily on the grounds that we assumed that different sources of data were conditionally independent given the climate sensitivity. While we consider this approximation to have been a reasonable one under the circumstances (and provided arguments to justify...

The equilibrium climate response to anthropogenic forcing has long been one of the dominant, and therefore most intensively studied, uncertainties in predicting future climate change. As a result, many probabilistic estimates of the climate sensitivity (S) have been presented. In recent years, most of them have assigned significant probability to e...

Henriksson et al. (2010), hereafter HALTL10, criticise Annan and Hargreaves (2006a) (AH06) primarily on the grounds that we assumed that different sources of data were conditionally independent given the climate sensitivity. While we consider this approximation to have been a reasonable one in the circumstances (and provided arguments to justify th...

Henriksson et al. (2010), hereafter HALTL10, criticize Annan and Hargreaves (2006a) (AH06) primarily on the grounds that we assumed that different sources of data were conditionally independent given the climate sensitivity. While we consider this approximation to have been a reasonable one under the circumstances (and provided arguments to justify...

Ecosystems give non-negligible influence on future climate change through their carbon budget and other processes, and contribution of their uncertainty is thought to be comparable to that of the climate sensitivity. On the other hand, Earth system models (ESM) based on state-of-the-art general circulation models (GCM) need large computational reso...

The use of information from paleoclimates as a means of assessing the performance of global climate models has long been considered an important motivation of paleoclimate research, but this topic has only recently become widely accepted in the mainstream climate modelling community. Several standard paleoclimate simulation experiments are for the...

The CMIP3 multi-model ensemble has been widely utilised for climate research and prediction, but the properties and behaviour of the ensemble are not well understood. Here we present a simple paradigm for assessing and interpreting the ensemble and show that the ensemble performs well under this paradigm, at least in terms of the model climatologie...

The present study considers the total amount of surface warming over Japan through analyzing the annual mean surface air temperature of 60 reliable synoptic stations that have records of 1870s onwards. The spatial pattern of up-to-date (1900-2009) observed warming over Japan depends significantly on size of population rather on latitude/longitude,...

By combining the strong points of general circulation models (GCMs), which contain detailed and complex processes, and Earth system models of intermediate complexity (EMICs), which are quick and capable of large ensembles, we have developed a loosely coupled model (LCM) which can represent the outputs of a GCM-based Earth system model using much sm...

Recent studies have indicated that the uncertainty in the global carbon cycle may have a significant impact on the climate. Since state of the art models are too computationally expensive for it to be possible to explore their parametric uncertainty in anything approaching a comprehensive fashion, we have developed a simplified system for investiga...

Analyses of skill are widely used for assessing weather predictions, but the time scale and lack of validation data mean that it is not generally possible to investigate the predictive skill of today's climate models on the multidecadal time scale. The predictions made with early climate models can, however, be analyzed, and here we show that one s...

The journal Geoscientific Model Development arose from the observation that despite modelling being central to climate/earth system science, the models themselves are not generally subject to the same level of scrutiny and peer review as the results they generate. Model descriptions are generally (with some exceptions) difficult to publish independ...

Efficient identification of parameters in numerical models remains a computationally demanding problem. Here we present an iterative Importance Sampling approach and demonstrate its application to estimating parameters that control the heat uptake efficiency of a physical/biogeochemical ocean model coupled to a simple atmosphere. The algorithm has...

The equilibrium climate sensitivity (ECS) of the two perturbed physics ensembles (PPE) generated using structurally different GCMs, Model for Interdisciplinary Research on Climate (MIROC3.2) and the Third Hadley Centre Atmospheric Model with slab ocean (HadSM3), is investigated. A method to quantify the shortwave (SW) cloud feedback by clouds with...

We consider paradigms for interpretation and analysis of the CMIP3 ensemble of climate model simulations. The dominant paradigm in climate science, of an ensemble sampled from a distribution centred on the truth, is contrasted with the paradigm of a statistically indistinguishable ensemble, which has been more commonly adopted in other fields. This...

We use an ensemble of runs from the MIROC3.2 AGCM with slab-ocean to explore the extent to which mid-Holocene simulations are relevant to predictions of future climate change. The results are compared with similar analyses for the Last Glacial Maximum (LGM) and pre-industrial control climate. We suggest that the paleoclimate epochs can provide some...

A study was conducted to investigate the performance of climate models from the Intergovernmental Panel for Climate Change (IPCC) assessment reports on the scale (6ox6o) of the Gangetic West Bengal region of east India. Climatological mean current climate ( 1961-90) of seasonal rainfall and temperature over the domain were compared with the results...

The equilibrium climate sensitivity (ECS) and climate feedback processes of the two perturbed physics ensembles (PPE) generated using structurally different GCMs, MIROC3.2 and HadSM3, are investigated. We develop a method to quantify the SW cloud feedback by clouds with different cloud top pressure. We find that the difference in the ensemble means...

We use an ensemble of runs from the MIROC3.2 AGCM with slab-ocean to explore the extent to which mid-Holocene simulations are relevant to predictions of future climate change. The results are compared with similar analyses for the Last Glacial Maximum (LGM) and pre-industrial control climate. We find evidence that the paleoclimate epochs can provid...

In a recent paper, Chylek and Lohmann (2008) used data from the Vostok ice core together with simple energy balance arguments to simultaneously estimate both the dust radiative forcing effect and the climate sensitivity, generating surprisingly high and low values for these respective parameters. However, their results depend critically on their se...