Publications by Myles Allen


Finding Ocean States That Are Consistent with Observations from a Perturbed Physics Parameter Ensemble

JOURNAL OF CLIMATE 31 (2018) 4639-4656

S Sparrow, RJ Millar, K Yamazaki, N Massey, AC Povey, A Bowery, RG Grainger, D Wallom, M Allen


Higher CO2 concentrations increase extreme event risk in a 1.5 degrees C world

NATURE CLIMATE CHANGE 8 (2018) 604-+

HS Baker, RJ Millar, DJ Karoly, U Beyerle, BP Guillod, D Mitchell, H Shiogama, S Sparrow, T Woollings, MR Allen


Human influence on climate in the 2014 southern England winter floods and their impacts

NATURE CLIMATE CHANGE 6 (2016) 627-+

N Schaller, AL Kay, R Lamb, NR Massey, GJ van Oldenborgh, FEL Otto, SN Sparrow, R Vautard, P Yiou, I Ashpole, A Bowery, SM Crooks, K Haustein, C Huntingford, WJ Ingram, RG Jones, T Legg, J Miller, J Skeggs, D Wallom, A Weisheimer, S Wilson, PA Stott, MR Allen


New use of global warming potentials to compare cumulative and short-lived climate pollutants

NATURE CLIMATE CHANGE 6 (2016) 773-+

MR Allen, JS Fuglestvedt, KP Shine, A Reisinger, RT Pierrehumbert, PM Forster


Attribution analysis of high precipitation events in summer in England and Wales over the last decade

CLIMATIC CHANGE 132 (2015) 77-91

FEL Otto, SM Rosier, MR Allen, NR Massey, CJ Rye, JI Quintana


Model structure in observational constraints on transient climate response

CLIMATIC CHANGE 131 (2015) 199-211

RJ Millar, A Otto, PM Forster, JA Lowe, WJ Ingram, MR Allen


Model structure in observational constraints on transient climate response

Climatic Change 131 (2015) 199-211

RJ Millar, A Otto, PM Forster, JA Lowe, WJ Ingram, MR Allen

© 2015, Springer Science+Business Media Dordrecht. The transient climate response (TCR) is a highly policy-relevant quantity in climate science. We show that recent revisions to TCR in the IPCC 5th Assessment Report have more impact on projections over the next century than revisions to the equilibrium climate sensitivity (ECS). While it is well known that upper bounds on ECS are dependent on model structure, here we show that the same applies to TCR. Our results use observations of the planetary energy budget, updated radiative forcing estimates and a number of simple climate models. We also investigate the ratio TCR:ECS, or realised warming fraction (RWF), a highly policy-relevant quantity. We show that global climate models (GCMs) don’t sample a region of low TCR and high RWF consistent with observed climate change under all simple models considered. Whether the additional constraints from GCMs are sufficient to rule out these low climate responses is a matter for further research.


weather@homedevelopment and validation of a very large ensemble modelling system for probabilistic event attribution

QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 141 (2015) 1528-1545

N Massey, R Jones, FEL Otto, T Aina, S Wilson, JM Murphy, D Hassell, YH Yamazaki, MR Allen


Anthropogenic influence on the changing likelihood of an exceptionally warm summer in Texas, 2011

GEOPHYSICAL RESEARCH LETTERS 42 (2015) 2392-2400

DE Rupp, S Li, N Massey, SN Sparrow, PW Mote, M Allen


Reply to 'Drivers of the 2013/14 winter floods in the UK'

NATURE CLIMATE CHANGE 5 (2015) 491-492

C Huntingford, T Marsh, AA Scaife, EJ Kendon, J Hannaford, AL Kay, M Lockwood, C Prudhomme, NS Reynard, S Parry, JA Lowe, JA Screen, HC Ward, M Roberts, PA Stott, VA Bell, M Bailey, A Jenkins, T Legg, FEL Otto, N Massey, N Schaller, J Slingo, MR Allen


THE HEAVY PRECIPITATION EVENT OF MAY-JUNE 2013 IN THE UPPER DANUBE AND ELBE BASINS

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 95 (2014) S69-S72

N Schaller, FEL Otto, GJ van Oldenborgh, NR Massey, S Sparrow, MR Allen


Potential influences on the United Kingdom's floods of winter 2013/14

NATURE CLIMATE CHANGE 4 (2014) 769-777

C Huntingford, T Marsh, AA Scaife, EJ Kendon, J Hannaford, AL Kay, M Lockwood, C Prudhomme, NS Reynard, S Parry, JA Lowe, JA Screen, HC Ward, M Roberts, PA Stott, VA Bell, M Bailey, A Jenkins, T Legg, FEL Otto, N Massey, N Schaller, J Slingo, MR Allen


Broad range of 2050 warming from an observationally constrained large climate model ensemble

Nature Geoscience 5 (2012) 256-260

DJ Rowlands, DJ Frame, D Ackerley, T Aina, BBB Booth, C Christensen, M Collins, N Faull, CE Forest, BS Grandey, E Gryspeerdt, EJ Highwood, WJ Ingram, S Knight, A Lopez, N Massey, F McNamara, N Meinshausen, C Piani, SM Rosier, BM Sanderson, LA Smith, DA Stone, M Thurston, K Yamazaki, Y Hiro Yamazaki, MR Allen

Incomplete understanding of three aspects of the climate system-equilibrium climate sensitivity, rate of ocean heat uptake and historical aerosol forcing-and the physical processes underlying them lead to uncertainties in our assessment of the global-mean temperature evolution in the twenty-first century 1,2. Explorations of these uncertainties have so far relied on scaling approaches 3,4, large ensembles of simplified climate models 1,2, or small ensembles of complex coupled atmosphere-ocean general circulation models 5,6 which under-represent uncertainties in key climate system properties derived from independent sources 7,9. Here we present results from a multi-thousand-member perturbed-physics ensemble of transient coupled atmosphere-ocean general circulation model simulations. We find that model versions that reproduce observed surface temperature changes over the past 50 years show global-mean temperature increases of 1.4-3 K by 2050, relative to 1961-1990, under a mid-range forcing scenario. This range of warming is broadly consistent with the expert assessment provided by the Intergovernmental Panel on Climate Change Fourth Assessment Report, but extends towards larger warming than observed in ensembles-of-opportunity 5 typically used for climate impact assessments. From our simulations, we conclude that warming by the middle of the twenty-first century that is stronger than earlier estimates is consistent with recent observed temperature changes and a mid-range 'no mitigation' scenario for greenhouse-gas emissions. © 2012 Macmillan Publishers Limited. All rights reserved.


Reconciling two approaches to attribution of the 2010 Russian heat wave

Geophysical Research Letters 39 (2012)

FEL Otto, N Massey, GJ Van Oldenborgh, RG Jones, MR Allen

In the summer 2010 Western Russia was hit by an extraordinary heat wave, with the region experiencing by far the warmest July since records began. Whether and to what extent this event is attributable to anthropogenic climate change is controversial. Dole et al. (2011) report the 2010 Russian heat wave was "mainly natural in origin" whereas Rahmstorf and Coumou (2011) write that with a probability of 80% "the 2010 July heat record would not have occurred" without the large-scale climate warming since 1980, most of which has been attributed to the anthropogenic increase in greenhouse gas concentrations. The latter explicitly state that their results "contradict those of Dole et al. (2011)." Here we use the results from a large ensemble simulation experiment with an atmospheric general circulation model to show that there is no substantive contradiction between these two papers, in that the same event can be both mostly internally-generated in terms of magnitude and mostly externally-driven in terms of occurrence-probability. The difference in conclusion between these two papers illustrates the importance of specifying precisely what question is being asked in addressing the issue of attribution of individual weather events to external drivers of climate. Copyright 2012 by the American Geophysical Union.


EXPLAINING EXTREME EVENTS OF 2011 FROM A CLIMATE PERSPECTIVE

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 93 (2012) 1041-1067

TC Peterson, PA Stott, S Herring, FW Zwiers, GC Hegerl, S-K Min, X Zhang, GJ van Oldenborgh, A van Urk, M Allen, C Funk, DE Rupp, PW Mote, N Massey, CJ Rye, R Jones, J Cattiaux, P Yiou, N Massey, T Aina, FEL Otto, S Wilson, RG Jones, N Christidis


Reconciling two approaches to attribution of the 2010 Russian heat wave

Geophysical Research Letters 39 (2012)

FEL Otto, N Massey, GJ Van Oldenborgh, RG Jones, MR Allen


Quantifying uncertainty in future Southern Hemisphere circulation trends

Geophysical Research Letters 39 (2012)

PAG Watson, DJ Karoly, MR Allen, N Faull, DS Lee

The Antarctic polar night jet has intensified during spring in recent decades due to stratospheric ozone depletion and rising greenhouse gas (GHG) concentrations and this has had substantial effects on the region's climate. GHG concentrations will rise over the 21st century whereas stratospheric ozone is expected to recover and there is uncertainty in future southern hemisphere (SH) circulation trends. We examine sensitivity to the physics parameterisation of the 21st century SH circulation projection of a coupled atmosphere-ocean General Circulation Model and the sensitivity of the contribution from stratospheric ozone recovery. Different model parameterizations give a greater range of future trends in the position of the tropospheric jet than has been found in previous multi-model comparisons. Ozone recovery causes a weakening and northward shift of the DJF tropospheric jet. Varying the physics parameterization affects the zonal wind response to ozone recovery of the SON stratosphere by ∼10% and that of the DJF troposphere by ∼25%. The projected future SAM index changes with and without ozone recovery and the SAM index response to ozone recovery alone are found to be strongly positively correlated with projected 21st century global warming. © 2012. American Geophysical Union. All Rights Reserved.


Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000.

Nature 470 (2011) 382-385

P Pall, T Aina, DA Stone, PA Stott, T Nozawa, AG Hilberts, D Lohmann, MR Allen

Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 1766, these floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at £1.3 billion (refs 5, 6). Although the flooding was deemed a 'wake-up call' to the impacts of climate change at the time, such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail to account fully for the complex hydrometeorology associated with flooding. Here we present a multi-step, physically based 'probabilistic event attribution' framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed computing, we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.


Warming caused by cumulative carbon emissions towards the trillionth tonne.

Nature 458 (2009) 1163-1166

MR Allen, DJ Frame, C Huntingford, CD Jones, JA Lowe, M Meinshausen, N Meinshausen

Global efforts to mitigate climate change are guided by projections of future temperatures. But the eventual equilibrium global mean temperature associated with a given stabilization level of atmospheric greenhouse gas concentrations remains uncertain, complicating the setting of stabilization targets to avoid potentially dangerous levels of global warming. Similar problems apply to the carbon cycle: observations currently provide only a weak constraint on the response to future emissions. Here we use ensemble simulations of simple climate-carbon-cycle models constrained by observations and projections from more comprehensive models to simulate the temperature response to a broad range of carbon dioxide emission pathways. We find that the peak warming caused by a given cumulative carbon dioxide emission is better constrained than the warming response to a stabilization scenario. Furthermore, the relationship between cumulative emissions and peak warming is remarkably insensitive to the emission pathway (timing of emissions or peak emission rate). Hence policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets. Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO(2)), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 degrees C above pre-industrial temperatures, with a 5-95% confidence interval of 1.3-3.9 degrees C.


Constraints on model response to greenhouse gas forcing and the role of subgrid-scale processes

Journal of Climate 21 (2008) 2384-2400

BM Sanderson, R Knutti, T Aina, C Christensen, N Faull, DJ Frame, WJ Ingram, C Piani, DA Stainforth, DA Stone, MR Allen

A climate model emulator is developed using neural network techniques and trained with the data from the multithousand-member climateprediction.net perturbed physics GCM ensemble. The method recreates nonlinear interactions between model parameters, allowing a simulation of a much larger ensemble that explores model parameter space more fully. The emulated ensemble is used to search for models closest to observations over a wide range of equilibrium response to greenhouse gas forcing. The relative discrepancies of these models from observations could be used to provide a constraint on climate sensitivity. The use of annual mean or seasonal differences on top-of-atmosphere radiative fluxes as an observational error metric results in the most clearly defined minimum in error as a function of sensitivity, with consistent but less well-defined results when using the seasonal cycles of surface temperature or total precipitation. The model parameter changes necessary to achieve different values of climate sensitivity while minimizing discrepancy from observation are also considered and compared with previous studies. This information is used to propose more efficient parameter sampling strategies for future ensembles. © 2008 American Meteorological Society.

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