Institute for Climate and Atmospheric Science (ICAS)

Physical Climate Change Group

July 2017: New article published in Earth and Planetary Science Letters journal

8,200 years ago, an abrupt reorganisation in Atlantic Ocean circulation caused the world to suddenly cool by 1-3 °C for ~160 years. Known as the 8.2 ka event, this rapid climate change has long been associated with the release of freshwater to the Labrador Sea as two North American proglacial lakes burst their banks. However, climate models have never been able to reproduce the 8.2 ka event using this forcing.

A study recently published in Earth and Planetary Science Letters (EPSL) by Matero et al. (2017) tested a hypothesis for an alternative forcing for the 8.2 ka event, successfully simulating the abrupt ocean circulation and climate changes more accurately than ever before. The authors, including Ilkka Matero, Lauren Gregoire and Ruza Ivanovic from the PCC group, argue that the lake outburst played only a minor role, and that the event was instead driven by meltwater from the collapse of an ice saddle connecting ice domes over the Hudson Bay. They forced the HadCM3 climate model with a meltwater pulse representing this saddle collapse, and their simulations match the magnitude and duration of changes recorded in the Greenland ice cores and sediment records from Europe and North Atlantic. These new forcing scenarios provide a means to reconcile longstanding mismatches between climate proxy data and models, allowing for a better understanding of the sensitivity of the climate models as well as the processes and feedbacks in motion during the disintegration of continental ice sheets in a warming world.

For more information see the full article.

Full article: 

June 2017: Owain Rutherford joins Physical Climate Change Group

Owain Rutherford has joined the PCC group for a 12 week summer placement as part of the Leeds-York NERC DTP Research Experience Placement scheme. Owain will be working with Dr Amanda Maycock, Dr Alex Rap, Dr Chris Smith and Prof Piers Forster to investigate the factors that affect the sensitivity of climate to perturbations in atmospheric gases. Owain will compute radiative forcing kernels for different gases using the SOCRATES radiative transfer model. Owain is currently a third year Mathematics and Theoretical Physics student at St Andrews University. 

Welcome to Leeds, Owain!

May 2017: New article published in Atmospheric Chemistry and Physics journal

New research has been published in ACP that diagnoses the radiative role of ozone and water vapour in the annual temperature cycle in the tropical tropopause layer (TTL).

There is a pronounced annual cycle in temperature in the TTL with an observed amplitude of around 8 K. This property of the atmosphere has long been attributed to adiabatic heating associated with the variation in the strength of upwelling in the tropical lower stratosphere over the year. However, new research by Ming et al. (2017), and including Amanda Maycock, uses satellite observations of atmospheric composition and modelling techniques to quantify the contribution of the annual cycles in ozone and water vapour in the tropical lower stratosphere to the annual cycle in TTL temperature. They find that around 30% of the observed annual cycle in temperature can be attributed to these radiative effects, thereby demonstrating this is an important mechanism for driving temperature variations in the TTL. For further details see the full article.

Ming, A., Maycock, A. C., Hitchcock, P., and Haynes, P.: The radiative role of ozone and water vapour in the annual temperature cycle in the tropical tropopause layer, Atmos. Chem. Phys., 17, 5677-5701, doi:10.5194/acp-17-5677-2017, 2017.

Understanding how precipitation responds to forcing is crucial for climate change prediction. Rainfall is not just affected by the gradual change in global temperatures, it also responds near-instantaneously to changes in the atmospheric energy budget. These rapid changes in response to forcing are known as precipitation adjustments, and they explain why precipitation responds so differently to different drivers. There are a number of methods which have been used for diagnosing precipitation adjustments in models, but it is unknown how these affect results. In a new study led by Tom Richardson, published in Journal of Geophysical Research Atmospheres, the different computation methods are assessed. It is shown that important physical and quantitative differences in results arise due to the method employed. For further details see the full article.

Richardson, T. B., B. H. Samset, T. Andrews, G. Myhre, and P. M. Forster (2016), An assessment of precipitation adjustment and feedback computation methods, J. Geophys. Res. Atmos., 121, 11,608–11,619, doi:10.1002/2016JD025625.

November 2016: New research makes recommendations for diagnosing effective radiative forcing from climate models

New research published in Journal of Geophysical Research Atmospheres makes recommendations for diagnosing effective radiative forcing from climate models for CMIP6.

The effective radiative forcing (ERF) is closely related to the eventual change in global-mean near-surface air temperatures. However, untangling the ERF from climate models has proved to be surprisingly difficult to achieve.

The team of researchers led by Piers Forster compared two widely-used methods for calculating ERF from climate models - fixing sea-surface temperatures (SSTs) to minimise surface temperature-driven feedbacks and taking the difference in top-of-atmosphere (TOA) energy balance, and allowing full coupled atmosphere-ocean runs for 100 years from which the ERF is calculated from a regression of TOA energy imbalance against changes in near-surface air temperature. It is found that the fixed-SST method produces estimates of ERF with a smaller range of uncertainty and fewer model simulation years than regression method. This is consistent for five different climate forcing agents (carbon dioxide, methane, black carbon, sulphate and solar radiation increase) in two climate models.

Furthermore, the actual sea-surface temperatures used in fixed-SST style ERF calculations has only a small effect on the ERF, allowing this method to be used to diagnose ERF in historical and future CMIP climate runs as well as idealised forcing experiments. Therefore, the fixed-SST method is recommended by the authors as the protocol for diagnosing ERF from climate models participating in CMIP6.

Forster, P. M., T. Richardson, A. C. Maycock, C. J. Smith, B. H. Samset, G. Myhre, T. Andrews, R. Pincus, and M. Schulz (2016), Recommendations for diagnosing effective radiative forcing from climate models for CMIP6, J. Geophys. Res. Atmos., 121, doi:10.1002/2016JD025320.

October 2016: New research on deep sea coral reveals insights into retreat of ice sheet

Image credit: L F Robinson

Uranium levels in deep sea coral reveal new insights into how the major northern ice sheets retreated

A team of scientists including Lauren Gregoire examining naturally occurring uranium levels in ancient deep sea corals have discovered new insights into how the major northern ice sheets retreated during the last major deglaciation on Earth. The findings were published in Science last week.

Subtle changes in seawater uranium isotopes can tell us about past changes in weathering on land. This is important because the input of material from the land to sea from weathering provides nutrients needed to support life in the ocean.

The team looked at 234U/238U reconstructions of the last 50,000 years based on the exceptionally well-preserved deep-sea corals from the equatorial North Atlantic and Pacific Galapagos platform. They hypothesized that the increase in excess uranium-234 during this time period was caused by the melting from the bottom of major ice sheets – it is in these areas where the large ice sheets has powdered the underlying rocks.

“A surprising result was that the Atlantic and Pacific records are different – only converging half way through the deglaciation.” says lead author, Dr Tianyu Chen, from the University of Bristol. This reflects past changes in ocean circulation.

This study has fundamentally changed our understanding of the behavior of U isotopes in the ocean, with importance for paleoclimatic reconstructions of nutrient fluxes to the oceans and U-series dating of marine materials.

Chen T; Robinson LF; Beasley MP; Claxton LM; Andersen MB; Gregoire LJ; Wadham J; Fornari DJ; Harpp KS (2016) Ocean mixing and ice-sheet control of last deglacial seawater ²³?U/²³?U evolutionScience,
DOI: 10.1126/science.aag1015.

Press release:

October 2016: New PhD students join Physical Climate Change Group

The Physical Climate Change group are happy to welcome 4 new PhD students this academic year.

Niall Gandy will work with Dr Lauren Gregoire to study the evolution of the British-Irish ice sheet at the end of the last ice age.

Andreas Chrysanthou will work with Dr Amanda Maycock and Prof Martyn Chipperfield to study modelled changes in the strength of the stratospheric overturning circulation under climate change.

Charlotte Weaver will work with Prof Piers Forster and members of the School of Engineering on novel strategies for bioenergy technologies.

Tom Wood will join the group in January 2017 and will work with Dr Amanda Maycock and Prof Piers Forster to use UKESM1 to study coupling between atmospheric composition and climate.

Welcome to the group Niall, Andreas, Charlotte and Tom!

The group would also like to congratulate Rhian Rees-Owen on her recent PhD viva success. Congratulations Dr Rees-Owen!

August 2016: New Research Assistant James Norton joins the team

James Norton has joined the School as a Research Assistant and will be supervised by Amanda Maycock and Suraj Dessai. Based in the Sustainability Research Institute James will be working on the EUPORIAS project, where his research will focus on decadal predictability and its potential uses for climate services. 

Humans have been emitting carbon dioxide (CO2) into the atmosphere for several hundred years through the combustion of fossil fuels and the burning of vegetation. But this CO2, the most important anthropogenic greenhouse gas, doesn’t just remain in the air forever; around half of it is taken up by the world’s oceans and continents.

Understanding the way these sinks of carbon work is vital when we are trying to predict how the climate will change in the future. Recent studies suggest that since the late 1980s the amount of carbon being taken up by the land carbon sink (i.e., soils, trees and other vegetation) has increased, by about 1 petagram (109 tonnes) of carbon per year. A recent study, led by Wolfgang Buermann and published in the EGU Journal Geosciences, sheds some light on the possible reasons for this shift.

Piers Forster joins 13 leading climate experts in sharing ‘gut feelings’ on equilibrium climate sensitivity with Bits of Science. Follow link for some interesting responses from a wide range of experts.

In this latest study, published in Nature Climate Change an international team of researchers including Head of the Leeds Physical Climate Change Group, Piers Forster, considered how the choice of metric can affect the relative emphasis placed on reductions of ‘cumulative climate pollutants’ such as carbon dioxide versus ‘short-lived climate pollutants’ (SLCPs), including methane and black carbon. The research showed that the widely used 100-year global warming potential (GWP100) effectively measures the relative impact of both cumulative pollutants and SLCPs on realized warming 20–40 years after the time of emission. If the overall goal of climate policy is to limit peak warming, GWP100 therefore overstates the importance of current SLCP emissions unless stringent and immediate reductions of all climate pollutants result in temperatures nearing their peak soon after mid-century, which may be necessary to limit warming to “well below 2?°C”. See Chris Mooney's comments on the study in the Washington Post.

Photograph by David Lynch

In this study recently published in Journal of Geophysical Research: Atmospheres, IAGP researchers Julia Crook, Lawrence Jackson and Piers Forster considered whether increasing the albedo and areal extent of existing ship wakes could reduce the temperature and precipitation changes caused by climate change. They showed wake albedo could be increased ten-fold by generating more and smaller bubbles than normally exist in wakes, but the areal extent would also need to be increased by at least 1000-fold to have a significant effect on global mean temperature. Increasing the areal extent this much using the same number of ships would require increasing the bubble lifetime in wakes from minutes to days (~10 days). This can only be achieved by the addition of surfactant – a chemical which helps stabilize microbubbles. The research has also been reported in the Huff Post.

Multi-model mean rapid precipitation adjustment in response to a quadrupling of CO2 levels

In a recent research article published in the Journal of Climate, Tom Richardson investigates what drives the spatial pattern of rapid precipitation adjustments in response to forcing agents such as CO2 and aerosols. Using state of the art climate models, it is shown that the spatial pattern is strongly influenced by rapid land surface temperature change. As a result, CO2 and aerosol forcing produce opposing spatial patterns. The rapid precipitation response to CO2 is found to be robust among models, with the largest changes occurring in the tropics. Co-authors include Piers Forster, Tim Andrews (Met Office) and Doug Parker. Full story.

Link to journal article. Link to blog post. 

This month sees the launch of the new Priestley International Centre for Climate Change (PICC) Doctoral Training Programme. 15 fully-funded PhD studentships, to start in October 2016, are available for a wide variety of climate-related projects. Successful applicants will join internationally leading research teams, undertaking ground-breaking research that seeks global climate solutions. The deadline for applications is 11 March 2016. For further details of all projects and to apply.

Holuhraun flood basalt eruption in Iceland in September 2014. Credit: Michelle Parks (University of Iceland)

Selective environmental stress from sulphur emitted by continental flood basalt eruptions

In this latest research article published in Nature GeoscienceDr Anja Schmidt challenges the previously understood role played by volcanism in causing mass extinctions. The team used a sophisticated computer simulation of the spread of the gas and aerosol particles which showed that the climatic impacts of flood basalts on plants and animals was potentially less severe than previously suggested. Interestingly the study also revealed that the destruction of vegetation by acid rain was less extensive than previously thought. Co-authors include Piers Forster and Alex Rap. Full story doi:10.1038/ngeo2588

Researchers in the Physical Climate Change Group are currently advertising a number of PhD research projects that span a broad range of exciting and novel research topics. These opportunities will enable to students to work with some of the leading academics and research groups in the UK.

They are offered by the Leeds York NERC Doctoral Training Partnership. The closing date for applications is 11 January 2016. The starting date is October 2016. Further details.

Securing Multidisciplinary UndeRstanding and Prediction of Hiatus and Surge events (SMURPHS)

Piers Forster will be Lead PI on a new NERC grant to begin December 2015. The research will aim to better understand the causes of periods where the rate of global-mean surface temperature is increased or decreased at decadal time-scales compared with long term (multi-decadal) trends. The work will seek to understand both the slowdown in the rate of warming since the late 1990s and also earlier hiatus and surge events.  Full story.

September 2015: Dr Amanda Maycock joins the Physical Climate Group

Amanda Maycock has recently joined the Physical Climate Group as a NERC Independent Research Fellow. Amanda completed her PhD at the University of Reading, and was most recently an AXA Research Fellow in the Centre for Atmospheric Science at the University of Cambridge. She has received funding for the next 5 years to undertake her fellowship on “Understanding and attributing composition-climate feedbacks in the Earth system”. Amanda will use the new UK Earth System Model 1 (UK-ESM1), currently being developed for the sixth Coupled Model Intercomparison Project (CMIP6), to study the impacts of anthropogenic forcing on climate. Her particular area of interest is on the role of feedbacks in atmospheric composition and interactions between stratospheric and tropospheric processes. We welcome Amanda to Leeds!

Feb 2015: Wait another 10 years and you will know the climate sensitivity

Our research published in Nature Geoscience today finds that uncertainty in radiative forcing will reduce with time, leading to better estimates of climate sensitivity.

Jan 2015: The haitus is not evidence that models overestimate warming

Observations suggest a slowdown in global surface temperature trends since 1998, whereas most climate models simulate continued warming. Some have speculated that this difference occurs because climate models overestimate climate change. Our new study gives a clear answer: There is no evidence for systematic model error and the observed discrepancy is mostly due to chance.

Read a summary here

Marotzke, J., and P.M. Forster, 2015: Forcing, feedback, and internal variability in global temperature trends. Nature, DOI 10.1038/nature14117


Jan 2015: Could we restore Arctic Sea Ice with Geoengineering?

In a paper just published in Geophysical Research Letters we perform a novel simulation where we see if it is possible to restore Arctic sea-ice using stratospheric aerosol injected by planes flying out of Svalbard. We treat a single model run as the real world and examine practical decision making under imperfect observations and incomplete understanding of climate response. We conclude that it will take over a decade to tell if interventions are effective. Further, uncertainty and arguments over the effectiveness and side effects precludes effective decision making.  This work was led by Lawrence Jackson as part of the IAGP project

December 2014: IAGP project results launched at Royal Society

We showcased results from are hugely successful IAGP project on geoengineering. Watch Vlog and download briefing notes from our Website. Also lots of media interest: Today Program, BBC TV, National press - see Website for details



November 2014: IPCC synthesis report published

After many sleepless nights the IPCC SYR report is approved, including Figure SPM.1, which had over 12 hours of heated debate! Read my account at Carbon Brief.

June 2014: Simple aerosol forcing diagnostics

Aerosol forcing components across models (Wm-2)

Our new paper led by Mark Zelinka from Lawrence Livermore used his Kernel approach to compare aerosol forcing and their affect on clouds across models. Understanding of aerosol cloud processes has long been hampered by different approaches used by different research groups. Here we show how using only simple diagnostics, aerosol radiative effects can be analysed in a simple way. This should lead to better understanding of model differences and help comparisons with observations of aerosol effects on climate. JGR in press version can be downloaded here.

Feb 2014: Papers published on emergent constraints for climate feebacks

Two papers published by the group in the last few months: Gordon et al. (Nov 2013, JGR) and Crook and Forster (Feb, 2014 GRL) look at if we can constrain water vapour and surface albedo feedbacks respectively using present day observations. The answer is a tentative yes for both these important climate feedbacks.

Gordon et al. used NASA satellite observationst observations to determine the strength of the water vapor feedback. According to our calculations, atmospheric water vapor amplifies warming by 2.2 ± 0.4 watts per square meter per degree Celsius. Using a series of climate models, we estimated the strength of the long term water vapor feedback of 1.9 to 2.8 watts per square meter per degree Celsius. In most models water vapour feedback derived from interannual variability got to within 15% of the long term feedback value within 25 years.

Crook and Forster found that Northern Hemisphere extratropical surface albedo feedback from recent climate change was considerably higher for observations than models, whereas the same feedback determined from the seasonal cycle is similar in observations and models. The work confirms the findings of a previous study (Flanner at al 2011) which estimated the feedback of Northern Hemisphere snow and ice albedo feedback using different observations and a different method. However, it casts some doubt on whether the seasonal cycle can be used to accurately predict the longer term climate change feedback as has been suggested by Qu and Hall (2006). The study also extends previous work by estimating the feedback in the Southern Hemisphere where the observed Antarctic sea ice feedback was found to be strongly positive in the seasonal cycle and similar to models.



Our new paper on CMIP5 radiative forcings is out in JGR

Forster, P. M., T. Andrews, P. Good, J. M. Gregory, L. S. Jackson, and M. Zelinka (2013), Evaluating adjusted forcing and model spread for historical and future scenarios in the CMIP5 generation of climate models, J. Geophys. Res. Atmos., 118, doi:10.1002/jgrd.50174

Bond et al. (2013) Bounding BC in the climate system is published. Free to download here. Thanks to everyone for their huge efforts over the last 4 years to bring this off- especially Tami!

Analysis of the latest climate model data by Lawrence Jackson and Piers Forster shows that droughts in Asia will become much more severe over the next decade, posing a great threat to food security of the region. We launch this new report today that highlights these near future timescales for the first-time. We find that a consistent pattern of increasing severe drought emegers, which poses a significant threat to wheat and maize harvests. China is best placed to adapt, Inida is not. The report can be downloaded from the Centre for Low-Carbon Futures website here.


Rapid adjustment review

New paper reviewing rapid adjustments to cloud, open access - so go ahead and download!

Professor Piers Forster has been awarded a Wolfson Research Merit Award by the Royal Society

15 November 2011

Professor Piers Forster in the School of Earth and Environment has been awarded a Wolfson Research Merit Award by the Royal Society. The scheme provides 5 years' funding for Prof Forster to continue working on climate change related issues. Jointly funded by the Wolfson Foundation and the Department for Business, Innovation and Skills (BIS), the scheme aims to provide universities with additional support to enable them to retain respected scientists of outstanding achievement

Forecasted PV and CSP outpurt changes

In her latest paper Julia Crook and colleagues examined how projected changes in temperature and insolation over the 21st century affeceted photovoltaic (PV) and concentrated solar power (CSP) output.  Our calculations indicate that  PV output from 2010 to 2080 is likely to increase by a few percent in Europe and China, see little change in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. CSP output is likely to increase by more than 10% in Europe, increase by several percent in China and a few percent in Algeria and Australia, and decrease by a few percent in western USA and Saudi Arabia. The results are robust to uncertainty in projected temperature change. A qualitative analysis of uncertainty in projected insolation change suggests strongest confidence in the results for Europe and least confidence in the results for western USA. 

Climate change impacts on future photovoltaic and concentrated solar power energy output

Julia A. Crook, Laura A. Jones, Piers M. Forster and Rolf Crook

Energy Environ. Sci., 2011, 4, 3101-3109

DOI: 10.1039/C1EE01495A

22 Sept 2011. Our ability to model past climates does not guarantee future success

PDFs for the Arctic and tropics mean 1918-1940 warming trends The dotted vertical lines show the observed trends

Julia Crook's latest paper from her PhD was published today in JGR (Crook and Forster, 2011) - and chosen to be specially highlighted by the editor. The paper shows that past trends in climate must be very carefully understood before using them to model the future. It was also the issues most downloaded paper.

See press release here.

Rhys Moore gets a Double Distinction!

Tony Windross and Rhys Moore with the Climate Change Machine

Rhys Moore helped build the climate change machine and used the ongoing trials and tribulations as the basis for his  BTEC National engineering certificate project. He did amazingly well in his BTEC and has earned an overall grade of "double dintinction", scoring an unbelievable 36 -double points for his project - well done Rhys!

Sept 2011. New ACP paper published

A new ACP paper published today estimates the aerosol indirect of carbonaceous aerosol for the first time. Dom Spracklen led the work. Alex Rap and Piers Forster performed the radiative forcing calculations.



July 2011. Well done Jonathan!

Jonathan Wild (Centre) with Dom Spracklen (left) and Piers Forster (right)
Jonathan Wild presented with an honorary degree by University of Leeds

Jonathan Wild, former chairman and chief executive of one of Yorkshire’s best-known businesses, Bettys & Taylors of Harrogate, was yesterday (14 July) presented with an honorary degree by the University of Leeds in recognition of his outstanding achievements.

The Honorary Doctorate of Laws was conferred upon Jonathan following his 30 year career with Bettys & Taylors.  During this time, the company was regularly featured in the Sunday Times ‘Best 100 Companies to work for’ list and in 2007 it was honoured at the highest level when it received its second Queen’s Award for Enterprise for Sustainable Development, only awarded to companies with the highest social and ethical values.

Jonathan is also a passionate conservationist and during the last 20 years he has led the company’s initiative to plant three million trees in tea and coffee growing countries around the world through the ‘Trees for Life’ scheme.  The business has now moved from planting trees to preventing their destruction with the launch of the Yorkshire Rainforest Project which aims to help save an area of rainforest the size of Yorkshire.

“It is, of course, a tremendous honour to be recognised in this way, particularly by such a great university.  I have seen firsthand some of the outstanding work carried out by its world-leading experts in the School of Earth and the Environment through their involvement in the United Bank of Carbon, a charity of which I am a trustee,” explains Jonathan. 

“The School has been instrumental in helping us to create the largest database of certified rainforest protection projects in the world which we are now seeking to partner with businesses.  It’s a great example of how businesses and the academic world can work together.”

Honorary degrees were also be conferred upon Corinne Bailey Rae; biologist Professor David Stuart; and NHS Director General of Research and Development, Dame Sally Davies.

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