The clustering of hot and cold IRAS galaxies: the redshift‐space correlation function
ABSTRACT We measure the autocorrelation function, j, of galaxies in the IRAS Point Source Catalog... more ABSTRACT We measure the autocorrelation function, j, of galaxies in the IRAS Point Source Catalogue galaxy redshift (PSCz) survey and investigate its dependence on the far-infrared colour and absolute luminosity of the galaxies. We find that the PSCz survey correlation function can be modelled out to a scale of 10 h 21 Mpc as a power law of slope 1.30^ 0.04 and correlation length 4.77^ 0.20. At a scale of 75 h 21 Mpc we find the value of J3 to be 1500^ 400.
Abstract Decadal predictions have a high profile in the climate science community and beyond, yet... more Abstract Decadal predictions have a high profile in the climate science community and beyond, yet very little is known about their skill. Nor is there any agreed protocol for estimating their skill. This paper proposes a sound and coordinated framework for verification of decadal hindcast experiments. The framework is illustrated for decadal hindcasts tailored to meet the requirements and specifications of CMIP5 (Coupled Model Intercomparison Project phase 5).
Abstract We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF... more Abstract We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF QSO Redshift Survey to test the hypothesis that there is a periodicity in the redshift distribution of quasi-stellar objects (QSOs) found projected close to foreground galaxies. These data provide by far the largest and most homogeneous sample for such a study, yielding 1647 QSO–galaxy pairs. There is no evidence for a periodicity at the predicted frequency in log (1+ z), or at any other frequency.
The potential to narrow uncertainty in regional climate predictions
Abstract Faced by the realities of a changing climate, decision makers in a wide variety of organ... more Abstract Faced by the realities of a changing climate, decision makers in a wide variety of organizations are increasingly seeking quantitative predictions of regional and local climate. An important issue for these decision makers, and for organizations that fund climate research, is what is the potential for climate science to deliver improvements-especially reductions in uncertainty-in such predictions?
Comment on “Multiyear prediction of monthly mean Atlantic Meridional Overturning Circulation at 26.5 N”
Abstract Matei et al.(Reports, 6 January 2012, p. 76) claim to show skillful multiyear prediction... more Abstract Matei et al.(Reports, 6 January 2012, p. 76) claim to show skillful multiyear predictions of the Atlantic Meridional Overturning Circulation (AMOC). However, these claims are not justified, primarily because the predictions of AMOC transport do not outperform simple reference forecasts based on climatological annual cycles. Accordingly, there is no justification for the “confident” prediction of a stable AMOC through 2014.
Projections of when temperature change will exceed 2°C above pre-industrial levels
Climate change projections are usually presented as' snapshots' of change at a particular time in... more Climate change projections are usually presented as' snapshots' of change at a particular time in the future. Instead, we consider the key question'when will specific temperature thresholds be exceeded?'Framing the question as' when might something happen (either permanently or temporarily)?'rather than'what might happen?'demonstrates that lowering future emissions will delay the crossing of temperature thresholds and buy valuable time for planning adaptation.
The time at which the signal of climate change emerges from the noise of natural climate variabil... more The time at which the signal of climate change emerges from the noise of natural climate variability (Time of Emergence, ToE) is a key variable for climate predictions and risk assessments. Here we present a methodology for estimating ToE for individual climate models, and use it to make maps of ToE for surface air temperature (SAT) based on the CMIP3 global climate models.
The possibility of a rapid collapse in the strength of the Atlantic meridional overturning circul... more The possibility of a rapid collapse in the strength of the Atlantic meridional overturning circulation (AMOC), with associated impacts on climate, has long been recognized. The suggested basis for this risk is the existence of two stable regimes of the AMOC ('on'and 'off'), and such bistable behaviour has been identified in a range of simplified climate models.
Future stratospheric ozone concentrations will be determined both by changes in the concentration... more Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone.
Abstract Future stratospheric ozone concentrations will be determined both by changes in the conc... more Abstract Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant 5 emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone.
Abstract Improved crop yield forecasts could enable more effective adaptation to climate variabil... more Abstract Improved crop yield forecasts could enable more effective adaptation to climate variability and change. Here, we explore how to combine historical observations of crop yields and weather with climate model simulations to produce crop yield projections for decision relevant timescales.
Abstract We compare future changes in global mean temperature in response to different future sce... more Abstract We compare future changes in global mean temperature in response to different future scenarios which, for the first time, arise from emission driven rather than concentration driven perturbed parameter ensemble of a Global Climate Model (GCM). These new GCM simulations sample uncertainties in atmospheric feedbacks, land carbon cy-5 cle, ocean physics and aerosol sulphur cycle processes.
Abstract Producing projections of future crop yields requires careful thought about the appropria... more Abstract Producing projections of future crop yields requires careful thought about the appropriate use of atmosphere-ocean global climate model (AOGCM) simulations. Here we describe and demonstrate multiple methods for 'calibrating'climate projections using an ensemble of AOGCM simulations in a 'perfect sibling'framework. Crucially, this type of analysis assesses the ability of each calibration methodology to produce reliable estimates of future climate, which is not possible just using historical observations.
Abstract Accurate decadal climate predictions could be used to inform adaptation actions to a cha... more Abstract Accurate decadal climate predictions could be used to inform adaptation actions to a changing climate. The skill of such predictions from initialised dynamical global climate models (GCMs) may be assessed by comparing with predictions from statistical models which are based solely on historical observations.
Estimating climatically relevant singular vectors for decadal predictions of the Atlantic Ocean
Bulletin of the American …, Jan 1, 2010
Abstract A key aspect in designing an efficient decadal prediction system is ensuring that the un... more Abstract A key aspect in designing an efficient decadal prediction system is ensuring that the uncertainty in the ocean initial conditions is sampled optimally. Here one strategy for addressing this issue is considered by investigating the growth of optimal perturbations in the third climate configuration of the Met Office Unified Model (HadCM3) global climate model (GCM). More specifically, climatically relevant singular vectors (CSVs)-the small perturbations of which grow most rapidly for a specific set of initial conditions-are ...
We describe a simple method that utilises the standard idea of bias-variance trade-off to improve... more We describe a simple method that utilises the standard idea of bias-variance trade-off to improve the expected accuracy of numerical model forecasts of future climate. The method can be thought of as an optimal multi-model combination between the forecast from a numerical model multi-model ensemble, on one hand, and a simple statistical forecast, on the other. We apply the method to predictions for UK temperature and precipitation for the period 2010 to 2100. The temperature predictions hardly change, while the precipitation predictions show large changes. * Correspondence
We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using ... more We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volumelimited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range 0:1 , ðr/ h 21 MpcÞ , 10. The clustering of L*ðM b J 2 5 log 10 h ¼ 219:7Þ galaxies in real space is well-fitted by a correlation length r 0 ¼ 4:9^0:3h 21 Mpc and power-law slope g ¼ 1:71^0:06. The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M*, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between M b J 2 5 log 10 h ¼ 218 and 222.5, and the most luminous galaxies are 3.0 times more strongly clustered than L* galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.
When climate forecasts are highly uncertain, the optimal mean squared error strategy is to ignore... more When climate forecasts are highly uncertain, the optimal mean squared error strategy is to ignore them. When climate forecasts are highly certain, the optimal mean squared error strategy is to use them as is. In between these two extremes there are climate forecasts with an intermediate level of uncertainty for which the optimal mean squared error strategy is to make a compromise forecast. We present two new methods for making such compromise forecasts, and show, using simulations, that they improve on previously published methods.
Our evolving climate is influenced by several factors such as greenhouse gases and solar output, ... more Our evolving climate is influenced by several factors such as greenhouse gases and solar output, coupled with the inherent variability of the climate system. Natural fluctuations in climate can temporarily mask or enhance the long-term upwards trend in temperatures, and contribute to uncertainty in climate projections, especially on regional scales. Understanding and acknowledging these variations is important for society and policymakers. This article aims to communicate the impacts of natural variability and discuss recent progress in understanding and predicting natural climate fluctuations. This progress offers potential to narrow uncertainty in climate predictions and may aid efficient adaptation to our changing climate.
The clustering of hot and cold IRAS galaxies: the redshift‐space correlation function
ABSTRACT We measure the autocorrelation function, j, of galaxies in the IRAS Point Source Catalog... more ABSTRACT We measure the autocorrelation function, j, of galaxies in the IRAS Point Source Catalogue galaxy redshift (PSCz) survey and investigate its dependence on the far-infrared colour and absolute luminosity of the galaxies. We find that the PSCz survey correlation function can be modelled out to a scale of 10 h 21 Mpc as a power law of slope 1.30^ 0.04 and correlation length 4.77^ 0.20. At a scale of 75 h 21 Mpc we find the value of J3 to be 1500^ 400.
Abstract Decadal predictions have a high profile in the climate science community and beyond, yet... more Abstract Decadal predictions have a high profile in the climate science community and beyond, yet very little is known about their skill. Nor is there any agreed protocol for estimating their skill. This paper proposes a sound and coordinated framework for verification of decadal hindcast experiments. The framework is illustrated for decadal hindcasts tailored to meet the requirements and specifications of CMIP5 (Coupled Model Intercomparison Project phase 5).
Abstract We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF... more Abstract We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF QSO Redshift Survey to test the hypothesis that there is a periodicity in the redshift distribution of quasi-stellar objects (QSOs) found projected close to foreground galaxies. These data provide by far the largest and most homogeneous sample for such a study, yielding 1647 QSO–galaxy pairs. There is no evidence for a periodicity at the predicted frequency in log (1+ z), or at any other frequency.
The potential to narrow uncertainty in regional climate predictions
Abstract Faced by the realities of a changing climate, decision makers in a wide variety of organ... more Abstract Faced by the realities of a changing climate, decision makers in a wide variety of organizations are increasingly seeking quantitative predictions of regional and local climate. An important issue for these decision makers, and for organizations that fund climate research, is what is the potential for climate science to deliver improvements-especially reductions in uncertainty-in such predictions?
Comment on “Multiyear prediction of monthly mean Atlantic Meridional Overturning Circulation at 26.5 N”
Abstract Matei et al.(Reports, 6 January 2012, p. 76) claim to show skillful multiyear prediction... more Abstract Matei et al.(Reports, 6 January 2012, p. 76) claim to show skillful multiyear predictions of the Atlantic Meridional Overturning Circulation (AMOC). However, these claims are not justified, primarily because the predictions of AMOC transport do not outperform simple reference forecasts based on climatological annual cycles. Accordingly, there is no justification for the “confident” prediction of a stable AMOC through 2014.
Projections of when temperature change will exceed 2°C above pre-industrial levels
Climate change projections are usually presented as' snapshots' of change at a particular time in... more Climate change projections are usually presented as' snapshots' of change at a particular time in the future. Instead, we consider the key question'when will specific temperature thresholds be exceeded?'Framing the question as' when might something happen (either permanently or temporarily)?'rather than'what might happen?'demonstrates that lowering future emissions will delay the crossing of temperature thresholds and buy valuable time for planning adaptation.
The time at which the signal of climate change emerges from the noise of natural climate variabil... more The time at which the signal of climate change emerges from the noise of natural climate variability (Time of Emergence, ToE) is a key variable for climate predictions and risk assessments. Here we present a methodology for estimating ToE for individual climate models, and use it to make maps of ToE for surface air temperature (SAT) based on the CMIP3 global climate models.
The possibility of a rapid collapse in the strength of the Atlantic meridional overturning circul... more The possibility of a rapid collapse in the strength of the Atlantic meridional overturning circulation (AMOC), with associated impacts on climate, has long been recognized. The suggested basis for this risk is the existence of two stable regimes of the AMOC ('on'and 'off'), and such bistable behaviour has been identified in a range of simplified climate models.
Future stratospheric ozone concentrations will be determined both by changes in the concentration... more Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone.
Abstract Future stratospheric ozone concentrations will be determined both by changes in the conc... more Abstract Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant 5 emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone.
Abstract Improved crop yield forecasts could enable more effective adaptation to climate variabil... more Abstract Improved crop yield forecasts could enable more effective adaptation to climate variability and change. Here, we explore how to combine historical observations of crop yields and weather with climate model simulations to produce crop yield projections for decision relevant timescales.
Abstract We compare future changes in global mean temperature in response to different future sce... more Abstract We compare future changes in global mean temperature in response to different future scenarios which, for the first time, arise from emission driven rather than concentration driven perturbed parameter ensemble of a Global Climate Model (GCM). These new GCM simulations sample uncertainties in atmospheric feedbacks, land carbon cy-5 cle, ocean physics and aerosol sulphur cycle processes.
Abstract Producing projections of future crop yields requires careful thought about the appropria... more Abstract Producing projections of future crop yields requires careful thought about the appropriate use of atmosphere-ocean global climate model (AOGCM) simulations. Here we describe and demonstrate multiple methods for 'calibrating'climate projections using an ensemble of AOGCM simulations in a 'perfect sibling'framework. Crucially, this type of analysis assesses the ability of each calibration methodology to produce reliable estimates of future climate, which is not possible just using historical observations.
Abstract Accurate decadal climate predictions could be used to inform adaptation actions to a cha... more Abstract Accurate decadal climate predictions could be used to inform adaptation actions to a changing climate. The skill of such predictions from initialised dynamical global climate models (GCMs) may be assessed by comparing with predictions from statistical models which are based solely on historical observations.
Estimating climatically relevant singular vectors for decadal predictions of the Atlantic Ocean
Bulletin of the American …, Jan 1, 2010
Abstract A key aspect in designing an efficient decadal prediction system is ensuring that the un... more Abstract A key aspect in designing an efficient decadal prediction system is ensuring that the uncertainty in the ocean initial conditions is sampled optimally. Here one strategy for addressing this issue is considered by investigating the growth of optimal perturbations in the third climate configuration of the Met Office Unified Model (HadCM3) global climate model (GCM). More specifically, climatically relevant singular vectors (CSVs)-the small perturbations of which grow most rapidly for a specific set of initial conditions-are ...
We describe a simple method that utilises the standard idea of bias-variance trade-off to improve... more We describe a simple method that utilises the standard idea of bias-variance trade-off to improve the expected accuracy of numerical model forecasts of future climate. The method can be thought of as an optimal multi-model combination between the forecast from a numerical model multi-model ensemble, on one hand, and a simple statistical forecast, on the other. We apply the method to predictions for UK temperature and precipitation for the period 2010 to 2100. The temperature predictions hardly change, while the precipitation predictions show large changes. * Correspondence
We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using ... more We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volumelimited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range 0:1 , ðr/ h 21 MpcÞ , 10. The clustering of L*ðM b J 2 5 log 10 h ¼ 219:7Þ galaxies in real space is well-fitted by a correlation length r 0 ¼ 4:9^0:3h 21 Mpc and power-law slope g ¼ 1:71^0:06. The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M*, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between M b J 2 5 log 10 h ¼ 218 and 222.5, and the most luminous galaxies are 3.0 times more strongly clustered than L* galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.
When climate forecasts are highly uncertain, the optimal mean squared error strategy is to ignore... more When climate forecasts are highly uncertain, the optimal mean squared error strategy is to ignore them. When climate forecasts are highly certain, the optimal mean squared error strategy is to use them as is. In between these two extremes there are climate forecasts with an intermediate level of uncertainty for which the optimal mean squared error strategy is to make a compromise forecast. We present two new methods for making such compromise forecasts, and show, using simulations, that they improve on previously published methods.
Our evolving climate is influenced by several factors such as greenhouse gases and solar output, ... more Our evolving climate is influenced by several factors such as greenhouse gases and solar output, coupled with the inherent variability of the climate system. Natural fluctuations in climate can temporarily mask or enhance the long-term upwards trend in temperatures, and contribute to uncertainty in climate projections, especially on regional scales. Understanding and acknowledging these variations is important for society and policymakers. This article aims to communicate the impacts of natural variability and discuss recent progress in understanding and predicting natural climate fluctuations. This progress offers potential to narrow uncertainty in climate predictions and may aid efficient adaptation to our changing climate.
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Papers by Ed Hawkins