This week, I participated in the first Overshoot Conference hosted by IIASA.
I’m looking forward to a full writeup of the conference outcomes because it became clear that while we are entering climate overshoot, and the urgency of action is never clearer, the concept of returning to 1.5C “from above” is still not mainstream, not in mitigation research and certainly not in policymaking.
A snap I took of one conference outcome went viral on Linkedin.
It shows a nice survey the conference oragnisers did of the participants at the start and end of the conference - what was our best guess in an optimistic and pessimistic scenario what would be the timing, peak and duration of peak temperatures, in a world where temperatures do return below 1.5C by 2500. The best guess of participants was that optimistically, tempertaures return to today’s levels by 2250 - that is in around 7 generations time, which is about the same distance from now as the start of the industrial revolution. This finding was very sobering for me - there is no likely “no or low overshoot” world now, and it’s honestly very difficult to see how humanity gets its act together to achieve this. Nevertheless, everyone there is doing what they can to avoid and minimise overshoot, which was comforting.
Very many thanks and kudos to the organisers, if you’re reading this, and thanks to the participants for an extremley enriching experience.
I gave the following paper:
Abstract - Towards a framework for aligning national mitigation scenarios with 1.5°C in an era of overshoot
While global integrated assessment models produce scenarios compatible with stabilising warming at 1.5°C, to what extent can – and do – national models? As the global community increasingly acknowledges that overshoot of 1.5°C is imminent, the interpretation and application of “highest possible ambition” as mandated by Article 4.3 of the Paris Agreement becomes critically important at national scales.
Recent commentary by Glen Peters underscores that global scenarios involving “impossibly steep emission declines to 1.5°C” offer limited practical guidance. Instead, more nuanced national scenarios, reflecting specific country circumstances and feasible ambition, are urgently needed. Achieving 1.5°C globally thus hinges on radical mitigation actions primarily implemented at the national level - scenarios that are “harder for researchers, but more confronting for policy makers”.
This paper addresses critical questions: Are national modelling and analytical frameworks adequately equipped to produce scenarios genuinely aligned with a 1.5°C future, particularly in the era of overshoot? What blind spots and methodological challenges hinder alignment? How can fairness, feasibility, and political acceptability be effectively reconciled in developing these scenarios?
Drawing from our experience working at Ireland’s “science-policy interface”, we propose a comprehensive set of criteria that national models and analytical frameworks should meet to credibly generate 1.5°C-aligned scenarios.
Ireland’s climate law requires legally binding carbon budgets aligned with the Paris Agreement. These budgets have been underpinned by iteratively-developed modelled pathways for energy, land-use, and food systems. Our experience highlights significant challenges in genuinely aligning these frameworks with the stringent demands of a 1.5°C future, and have succeeded, in our view, only partially.
Drawing from these lessons, the proposed framework encompasses four key elements:
- Alignment with 1.5°C & transparent equity assessment: Clearly define and justify how national emission and removal pathways contribute fairly to a global 1.5°C outcome, explicitly reflecting equity principles such as historical responsibility, capability, and equality. Given overshoot realities, frameworks must address not just emissions reductions but equitable responsibilities for carbon drawdown and non-CO₂ mitigation, especially for high-income countries with historical carbon debt. Consider the role of methane reduction to limit peak warming
- Expanded mitigation space & feasibility: Explore broader mitigation spaces, including radical demand reduction and structural changes beyond incremental technology substitution. Explicitly assess: • Expanded CDR options • Maximum plausible clean technology diffusion • Low-demand scenarios • Explicit mitigation of residual emissions
- Coverage of greenhouse gases and sectors: Include all relevant sectors and gases typically underrepresented in national scenarios, such as Agriculture, Forestry and Other Land Use (AFOLU), international aviation and shipping, bioenergy, hydrogen trade, and short-lived non-CO₂ gases.
- Integration and sectoral coherence: Ensure coherent integration across sectors, particularly regarding land use, sustainable resource use and management of biogenic carbon (and its role in carbon drawdown, bioenergy, terrestrial carbon sinks and CDR), and reflecting integrated land-energy-food system interactions. This framework aims to shift the Overton window towards scenarios genuinely reflective of the “highest possible ambition” in the critical decade ahead, aligning national actions transparently and fairly, to better confront policymakers with choices and trade-offs.