A number of the latest generation climate models (CMIP6) project greater future warming than previously assessed, but drawing conclusions about the implications for emission reduction targets is premature.

The higher warming these new models project is due to higher climate sensitivity, which might be partly explained by how these models incorporate new knowledge about the interactions between clouds and the climate.

A growing number of studies suggest that CMIP6 model sensitivities might lead to overestimating future warming. More importantly however, the change in the quantity in CMIP6 models, which is relevant for calculating carbon budgets - the transient climate response to emissions (TCRE) - may be smaller than the potential increase in long-term equilibrium warming.

Preliminary results based on a limited set of models suggest that even TCRE estimates from more sensitive CMIP6 models, if proven correct, would only reduce the best estimate for the 1.5°C carbon budget by a few percent. These differences are very small compared with the uncertainties surrounding these carbon budget estimates, and do not allow for any robust conclusions. If anything they only re-emphasise the need for stringent near-term emission reductions to achieve the Paris Agreement goal.

The world is 1°C warmer than pre-industrial levels and continues to warm at about 0.2°C per decade. Slowing down warming over the next decades is crucial to limit warming to 1.5°C. Stringent emission reductions, as implied by Paris Agreement compatible pathways, can reduce near-term warming rates by up to 50%. Near-term emissions reductions are key to keep the Paris Agreement’s long-term temperature goal in sight.

The Intergovernmental Panel on Climate Change (IPCC), the United Nations body for assessing the latest climate change science, will release its 6th Assessment Report (AR6) in 2021. A great deal of the findings in AR6 will be based on the latest generation of climate models from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). Therefore, it is crucial to assess whether these models provide a better representation of the climate system and offer more realistic projections of global warming than their predecessors.

The 1.5°C limit and risks of overshoot

This briefing looks at what the 1.5°C limit means in terms of adaptation and loss and damage for the most vulnerable countries and regions. It finds that slowing down warming is critical to buy us time to adapt and also to avoid irreversible loss and damage. Even if warming rises above 1.5°C (overshoot) we can bring it down again with ambitious emissions reductions.

Le seuil de +1,5°C et le risque de dépassement de ce seuil

Ce rapport examine ce que la limite de 1,5 °C signifie en termes d'adaptation et de pertes et dommages pour les pays et régions les plus vulnérables. Il constate qu'il est essentiel de ralentir le réchauffement pour nous donner le temps de nous adapter et pour éviter des pertes et des dommages irréversibles. Même si le réchauffement dépasse 1,5 °C, nous pouvons le faire baisser à nouveau en réduisant les émissions de manière ambitieuse.

Kipppunkte und kaskadische Kippdynamiken im Klimasystem

Dieser im Auftrag des deutschen Umweltbundesamtes erstellte Bericht befasst sich mit Kippelementen - sensible Komponenten des Erdsystems, die bei Überschreiten kritischer Schwellenwerte (Kipppunkte) irreversiblen Veränderungen ausgesetzt werden können. Er unterstreicht, dass selbstverstärkende Mechanismen zwischen diesen Elementen zu schnellen, irreversiblen Veränderungen führen können.

Limited reversal of regional climate signals in overshoot scenarios

This peer-reviewed paper analyses what happens in an 'overshoot scenario' - where temperature rise peaks just above 1.5°C, but then return below it by the end of the century. It concludes that despite a drop in warming, regional climate changes may only be partially reversed in the decades after peak warming, demonstrating the value of limiting peak temperatures to as low as possible.

Uncompensated claims to fair emission space risk putting Paris Agreement goals out of reach

Based on scenarios underlying the IPCC's 6th Assessment Report, in this paper we construct a suite of scenarios that combine the following elements: (a) two quantifications of a moral claim to the remaining carbon space by South Asia, and Africa, (b) a 'highest possible emission reduction' effort by developed regions, and (c) a corresponding range for other developing regions. Our findings raise important questions of perspectives on equity in the context of the Paris Agreement including on the critical importance of climate finance.

Institutional decarbonisation scenarios evaluated against the Paris Agreement 1.5°C goal

This study analyses six institutional decarbonisation scenarios published between 2020 and mid 2021 (including four from the oil majors and two from the International Energy Agency. It finds that most of the scenarios would be classified as inconsistent with the Paris Agreement as they fail to limit warming to ‘well below 2 ̊C, let alone 1.5 ̊C, and would exceed the 1.5 ̊C warming limit by a significant margin.

About us

Decarbonisation targets and 1.5℃ pathways

Comment

New models, old message: deep emission cuts in next decade are key

Publications

The 1.5°C limit and risks of overshoot

Le seuil de +1,5°C et le risque de dépassement de ce seuil

Kipppunkte und kaskadische Kippdynamiken im Klimasystem

Limited reversal of regional climate signals in overshoot scenarios

Adjusting 1.5°C climate change mitigation pathways in light of adverse new information

2030 targets aligned to 1.5°C: evidence from the latest global pathways

The deployment length of solar radiation modification: an interplay of mitigation, net-negative emissions and climate uncertainty

Uncompensated claims to fair emission space risk putting Paris Agreement goals out of reach

Only halving emissions by 2030 can minimise risks of crossing cryosphere thresholds

1.5°C is still in reach to reduce the worst climate risks – but only with immediate mitigation action and shifting finance

How can the EU transform its economy to meet the 1.5°C goal?

Institutional decarbonisation scenarios evaluated against the Paris Agreement 1.5°C goal