IPCC (AR5) report - the foundation for the Paris Agreement

Professor Gabi Hegerl's seminal work has pioneered the method to detect the 'human fingerprint' in anthropogenic climate change through combining observations and climate model simulations.

Her method has become one of the central pillars of climate science. 

Since then, our researchers have played a significant role in determining critical relationships between greenhouse gas emissions and climate warming. We made crucial contributions to estimating the 'human fingerprint' in the climate system from observed change. This also included methods for estimating climate sensitivity, which is how much greenhouse gas emissions warm the climate.

We achieved this through world-leading analysis synthesising multiple sources of evidence, including:

1. ​​​​​​ observed warming in the pre-and post-industrial period paleoclimate
2. instrumental records
3. physical understanding derived from worldwide modelling approaches. 

This led to the quantification of the Equilibrium Climate Sensitivity (ECS) – a key climate metric showing how how much greenhouse gas emissions warm the climate.

Our work was used as evidence in the IPCC Fifth Assessment (AR5) reports which underpinned the Paris Agreement.

The IPCC exclusively selected Professor Hegerl for the Core Author Team of the AR5 Synthesis Report, the overarching and top-level document of the IPCC 5th Assessment Report. She also led the section on observed emissions and changes in the climate in the report. 

In addition, Professor Hegerl led the Guidance Paper on the attribution of observed climate change and impacts to causes for use across the IPCC's working groups.  It was widely used and cited in the overarching IPCC 5th Assessment Report and is still used today, including the latest Sixth Assessment Report (AR6).  

At the Approval Plenary for the report involving all the United Nations country delegations, Professor Gabi Hegerl presented the keynote presentation on climate sensitivity. It was one of only four key science presentations given to directly communicate the report's findings to the full plenary session of government representatives.​​​​​

Our researchers have made vital contributions to the  IPCC Fifth Assessment Report (AR5), which was the scientific foundation for the 2015 Paris Agreement of the United Nations Framework Convention on Climate Change.

The Paris Agreement is the first-ever universal, legally binding global climate change agreement, adopted at the Paris climate conference (COP21) in December 2015.  

Its goal is to limit global warming to well below 2, preferably to 1.5 degrees Celsius, compared to pre-industrial levels. It also aims to strengthen countries' ability to deal with climate change impacts and support them in their efforts.

The Paris Agreement is a landmark for climate change. For the first time, a binding agreement brings all nations into a common cause to undertake ambitious efforts to combat climate change and adapt to its effects.  Implementation of the Paris Agreement requires economic and social transformation based on the best available science. 

Reducing warming to 1.5 degrees C

Following the Paris Agreement, the United Nations Framework Convention on Climate Change requested advice from the IPCC to limit climate warming to well below 2, preferably to 1.5 degrees Celsius.

The IPCC aimed to assess the impacts of global warming of 1.5 degrees Celsius above pre-industrial levels and related global greenhouse gas emission pathways.

Subsequent research by our School estimated the variation in the Earth's pre-industrial climate.  We attributed observed variations in climate to radiative forcing, and estimated detectable greenhouse gas contributions to surface temperature from across the 19th century.  

This research is important because it is the baseline used by the IPCC to assess climate change stabilisation targets. 

Analysis of the pre-industrial climate led our researchers to conclude that correcting this baseline reduced the amount of warming in future by 0.2 degrees before the Paris Agreement targets are exceeded. In addition, this correction meant that there was a corresponding reduction of up to 40% in the remaining future budget for carbon dioxide emissions.

The resulting 2018 landmark IPCC Special Report 'Global Warming of 1.5 Degrees C', was arguably one of the most important and influential reports in the IPCC's history.

The IPCC cited work from our University researchers, including findings applied directly in calculating future emissions allowable without exceeding 1.5C warming.  

This Working Group assesses the physical scientific basis of the climate system and climate change.

• Professor Gabi Hegerl was selected as:

  • Draft Contributing Author (Summary)

  • Lead Author for 'Chapter 10: Detection and attribution of climate change from global to regional'

  • Contributing Author for 'Chapter 12: Long-term climate change: projections, commitments and irreversibility'

  • Expert Reviewer

• Professor David Stevenson was selected as:

  • Contributing Author for ‘Chapter 8: Anthropogenic and natural radiative forcing’

  • Contributing Author for ‘Chapter 11: Near-term climate change: projections and ​​​​​​predictability’

  • Contributor to ‘Annex II: Climate system scenario tables’

  • Expert Reviewer 

• Dr Andrew Schurer was selected as Contributing Author for 'Chapter 10: Detection and attribution of climate change from global to regional'

• Dr Peter Alexander was selected as Contributing Author

• Professor Ruth Doherty was selected as Expert Reviewer 

• Dr Massimo Bollasina was selected as Expert Reviewer 

• Professor Richard Essery was selected as Expert Reviewer 

• Professor Dave Reay was selected as a Expert Reviewer 

Our research

The IPCC recognised and cited the work by our researchers throughout this report.

You can find out more about their research under each of their profiles below:

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This Working Group assesses the impacts, adaptation and vulnerabilities of socio-economic and natural systems related to climate change.

• Professor Mark Rounsevell was selected as Lead Author
• Dr Meriwether Wilson was selected as Contributing Author for 'Chapter 23: Europe'
• Professor Marc J Metzger was selected as Contributing Author for 'Chapter 23: Europe'
• Professor Murray Roberts was selected as:
  • Contributing Author for 'Chapter 6: Ocean Systems' 
  • Expert Reviewer

Our research

The IPCC recognised and cited the work by our researchers throughout this report.

You can find out more about their research under each of their profiles below:

​​​​

Working Group III assesses all relevant options for mitigating climate change through limiting or preventing greenhouse gas emissions and taking actions to remove them from the atmosphere

• Dr Saran Sohi was selected as Contributing Author for 'Chapter 11: Agriculture, Forestry and other land use.'

The IPCC recognised and cited the work by our researchers throughout this report.

You can find out more about their research under each of their profiles below:

Sixth Assessment Report (AR6)

In August 2021, the IPCC published the first instalment, 'The Physical Science Basis', of its long-awaited Sixth Assessment Report (AR6).

It is eight years since the IPCC's fifth assessment of climate science (AR5). Therefore the new report benefits from almost a decade of work of additional research, observations and technological progress.

We've provided highlights on the latest report:

Starkest warning yet - what our research and latest IPCC (AR6) report reveals

Special Reports

Between the Assessment Reports, the IPCC also publishes Special Reports which focus on a specific issue.  

Since the Fifth Assessment Report (AR5), the IPCC has produced three Special Reports:

1. Global Warming of 1.5 Degrees C (2018)
2. Climate Change and Land (2019)
3. Ocean and Cryosphere in a Changing Climate (2019

We are among the world-leading researchers who have made crucial contributions to the IPCC's Special Reports, guiding policies around the globe.

For example, the 2018 landmark IPCC Special Report 'Global Warming of 1.5 Degrees C', was arguably one of the most important and influential reports in the IPCC's history.  The IPCC cited work from our University researchers, including findings applied directly in calculating future emissions allowable without exceeding 1.5C warming.  

We've provided highlights on the Special Reports:

IPCC Special Reports