Impact case study database

Informing the Paris Agreement

UoE research on the effect of increasing greenhouse gases on past and future climates and precipitation patterns has made vital contributions to reports of the Intergovernmental Panel on Climate Change (IPCC) since August 2013, with the team’s “ contribution to the IPCC and public policy” judged “substantial and a very good example of innovative and policy relevant research” [5.1]. The IPCC reports directly informed the international climate change negotiations which resulted in the 2015 United Nations Paris Agreement treaty on climate change. The Paris Agreement is the overarching global framework for addressing climate change, with 194 states and the European Union (EU) as signatories in 2015. Of these, 187 states and the EU, representing about 79% of global greenhouse gas emissions, have now ratified or acceded to the Agreement.

Professor Hegerl was a lead author of the IPCC’s Working Group 1 Report on Climate Change 2014 - the Physical Science Basis, published in June 2014 [5.2]. This report provides a comprehensive assessment of the physical science basis of climate change since 2007 when the Fourth Assessment Report (AR4) was released. She was selected for her role based on her scientific output on the causes of climate change. Among the IPCC authors she was selected for the author team of the AR5 Synthesis Report: Climate Change 2014 [5.2], and led the section on observed emissions and changes in the climate in that report. The AR5 Synthesis Report (approved in the IPCC plenary meeting in October 2014), is the overarching and top-level document of the IPCC 5^th Assessment Report, which “ was the scientific foundation for the Paris Agreement of the United Nations Framework Convention on Climate Change” [5.3]. The Working Group 1 co-chair describes her “ seminal work that has transformed our field… you have pioneered the method to detect fingerprints of anthropogenic climate change combining observations and climate model simulations..this [method] has become one of the central pillars of climate science” [5.3]. Altogether the IPCC 5^th Assessment Report [5.2] contains 18 citations of Professor Hegerl, 2 of Professor Tett, 3 of Dr Polson and 1 of Dr Schurer (allocated to first author listed only to avoid duplication), and the Edinburgh team has provided 3 figures. In particular, an update to [3.2] provided a key figure in the IPCC 5th Assessment Report, which was also reproduced in the Technical Summary as figure TFE6.1, and [3.1- 3.6] are all cited in IPCC 5th Assessment Report, or the 1.5 degree special report [5.2].

Professor Hegerl also led the Guidance Paper on attribution of observed climate change and impacts to causes for use across the IPCC’s working groups, which was widely used and cited in the overarching IPCC 5^th Assessment Report. At the approval plenary for the report involving all the United Nations country delegations she presented the keynote presentation on climate sensitivity. This was one of only four key science presentations given to directly communicate the report’s findings to full plenary session of Government representatives [5.2, 5.3]. Professor Tett was selected to be an expert review editor for the 2014 IPCC 5^th Assessment Report, Working Group I. The former Head of Science at the Department of Energy and Climate Change describes the two key issues that the UoE team highlighted – climate sensitivity [3.1,3.2] and event attribution [5.5], as “ key policy issues which affect both the scale and urgency required of the response to climate change internationally… the agreement that was reached to limit the global temperature rise to 2C above pre-industrial levels (and to aim for as close to 1.5C as possible) and achieve net zero emissions in the second part of the 21^st Century, drew directly on this and similar work” [5.1].

Following the Paris Agreement, the United Nations Framework Convention on Climate Change requested advice from the IPCC on the target of limiting climate warming to 1.5 degrees C. The resulting 2018 landmark IPCC special report on Global Warming of 1.5 degrees C (1.5C Report), arguably one of the most important and influential reports in the IPCC’s history, cited four papers from UoE climate researchers, with findings from [3.5] applied directly in the calculation of the future emissions allowable without exceeding 1.5C warming. The 1.5C report has guided climate change policies across the globe including, via assessment by the UK Committee on Climate Change, the UK Parliament strengthening its climate target in June 2019 by passing legislation requiring the government to reduce the UK's net emissions of greenhouse gases by 100% relative to 1990 levels by 2050. This was described as the ‘ defining decision of this generation in fulfilling our responsibility to the next’ by Prime Minister Theresa May. [5.4].

Contribution to national policymaking

The UoE team’s research identifying human influence in extreme weather events has successfully engaged policymakers in the immediate risks and damages resulting from climate change. Professor Hegerl was on the committee (one of ten) that produced the 2016 US National Academies review on extreme weather event attribution [5.5], which cites 10 of her papers (5 as first author or principal supervisor; incl. **[3.6]**) as well as the IPCC guidance document [5.2]. This report reached the major conclusion that it is now possible to identify the role of climate change in individual extreme events. The report is “ by all metrics, […] among the most impactful contributions of the National Academies in the past decade” and was widely reported and communicated to US agencies and policymakers. It was downloaded more than 27,000 times by October 2020, ranking it as the most downloaded Earth Science report, and in the top 1% of all National Academies’ products. It was also covered by 300 news outlets, with “ multiple mentions by leading outlets including the New York Times, Washington Post, Forbes and CNN”. It was briefed to numerous audiences, including multiple US government agencies, staff from House and Senate committees, and the White House Office of Science and Technology Policy. [5.6]. The report also underpinned the international development of an operational event attribution capability that can rapidly assess the factors contributing to extreme events. This “ enables analyses to be completed quickly after an event, leading to more direct connection to climate change” in media communication about an extreme event. The work was named as one of the top ten breakthrough technologies by the MIT Tech Review in 2020 [5.6]. Professor Hegerl also wrote the section on changes in climate extremes of the Climate Updates report by the Royal Society. This was used to inform policymakers ahead of the 2017 Bonn COP23 on scientific developments in the understanding and prediction of climate change since the 2014 IPCC 5th Assessment Report [5.7].

The team’s research into extreme events and climate sensitivity has further contributed to international reports (eg Figure 10.11 in the 5^th IPCC Report [5.2] is adapted from [3.3]. Professor Hegerl chaired the scientific review group for the UK Met Office Hadley Centre 2014-2017 (review group member from 2008) [5.1], and was a review group member for the recently released UK climate predictions 2018 (UKCP18) [5.8] which provide quantitative climate change predictions for UK policymakers and stakeholders informing major decisions on climate change adaptation e.g. managing flood risk and rising sea levels.