Attributing and predicting changes in the probability of climate extremes

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences


We plan to address the following research questions:
- in which regions are the frequency and intensity of heat waves and cold spells increasing?
- Are climate models able to reproduce these changes?
- Can we improve their prediction if using initialized climate forecasts?

This work extends in scope and regions studied two existing projects: The first one is the EQUIP project, which predicts changes in European and UK heatwaves and drought. We propose to extend this work by also studying North America and East Asia. These regions show tentative evidence that mean temperature is better predictable by initialized than forced runs over the near-term (about 5 years; e.g., D. Matei; J. Marotzke, pers. Com.). These regions also show interesting and challenging changes in observed patterns of frequency and intensity of temperature extremes . The second project we plan to build on is a project that works towards attributing changes in worldwide frequency of hot and cold extremes, and this proposal extends her work from use of a single model (HadGEM1) to use of the CMIP5 archive. This will much increase the impact of her results, and provide highly relevant information to the authors of IPCC chapters 10 and 11 (see pathways to impact).

Planned Impact

The main target for impact for this proposed work is the IPCC 5th Assessment report. Hegerl is a Lead Author of the chapter on Detection and Attribution of Climate Change: From global to regional, a chapter which has in its draft outline a section on attribution of changes in climate extremes for which our results will clearly be relevant (see also attached letter by Peter Stott, Coordinating Lead Author of that chapter). The results based on the Decadal predictions will be relevant for chapter 11, Near-term climate change: Projections and Predictability. Provisional results from some modelling centers show evidence that mean temperatures on the Pacific Rim of North America and Asia have significant predictability a few years into the future (D. Matei and Jochem Marotzke, pers. Com.) which we hope to make use of. This chapter will also be interested in our results.
We also have good contacts to the Human Health community, e.g. Gavin Donaldson, through EQUIP and will communicate our results via those channels.


10 25 50
Description European summer mean and extreme temperatures have changed significantly in many regions, in a way consistent with expectation due to external drivers. These changes lead to predictive skill for the future. However, using data from multiple models shows that the skill varies by model. In all models and most regions, there is skill on the 5-10yr timescale originating from external forcing, leading to a general tendency for hot extremes to become more likely. Including that in models improves their skill in forecasts. In contrast, the additional skill gained by initializing the model with observed surface conditions varies from model to model and is often small or insignificant relative to that gained from accounting for forcing such as increasing greenhouse gases. The results also show that recent observed changes in the frequency / intensity of hot extremes have been caused by external forcing, dominated by anthropogenic forcing.
Exploitation Route Publication in review; results show that prediction of heat waves nearterm (5-10yrs) benefit from accounting for human influences particularly greenhouse gas forcing
Sectors Agriculture, Food and Drink,Environment

Description Results from this publication have been cited by the Intergovernmental Panel on Climate Change 5th's Assessment report in the Detection and Attribution chapter (ch10; WGI report) and in ch11.
First Year Of Impact 2013
Sector Agriculture, Food and Drink,Environment,Government, Democracy and Justice,Transport
Impact Types Societal,Economic

Description Intergovernmental Panel on Climate Change (IPCC) Lead Author and member of Synthesis report writing team.
Geographic Reach Multiple continents/international 
Policy Influence Type Membership of a guideline committee
Impact PI was involved in Intergovernmental Panel on Climate Change (IPCC)'s fifth Assessment report, as a Lead Author and in the Synthesis report, released 2015, as a writing team member. These reports arguably form the basis of the Paris Agreement on climate change, and authors are chosen for their scientific contributions to the area they are chosen for. Hence this relates directly to my publications under these grants.
Description Climate Change: Science and Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Climate Change: Science and Society: This was a half day conference under the auspices of the Royal Society of Edinburgh. I was a coorganizer and speaker see website report. It was well attended and well received and communicated the state of climate science, impact and mitigation knowledge on climate change to the wider public
Year(s) Of Engagement Activity 2015