"Large uncertainties" over warming outcomes from current climate policies

Credit: Trevor Bexon (Shutterstock)

There is a risk that "false precision" in the reporting of climate policy outcomes could lead to complacency by governments, researchers have warned.

A new analysis by researchers from the EU Horizon 2020 project 'Paris Reinforce', including Imperial College London's Dr Ajay Gambhir, has found that the impact of climate policies is more uncertain than is often assumed by policymakers.

The study, published in the journal Nature Climate Change, looked at current policies and countries' pledges (known as Nationally Determined Contributions) to reduce the carbon emissions that cause global warming between now and 2030. It used a diverse set of Integrated Assessment Models (IAMs) to predict the implied effect on global warming from 2030 to 2100 - finding a wide range in outcomes.

The researchers say their findings reaffirm and highlight the extent of uncertainty in predicting warming outcomes from climate policies, which have come under intense scrutiny following the United Nations Climate Change Conference (COP26) in Glasgow earlier this month.

Dr Ida Sognnaes, a Senior Researcher at the CICERO Center for International Climate Research in Oslo, Norway, and lead author of the study, said: "During COP26, a succession of studies confidently communicated that current policies would lead to 2.7°C of warming in 2100 and emission pledges to 2.4°C of warming, while we find that the uncertainties are much greater and that the answer depends on what model is used."

The findings showed a wide range of possible scenarios emerging from the selected models, with current policies leading to between 2.3 and 2.9°C of warming in 2100, and pledges on carbon emissions leading to between 2.2 and 2.7°C.

Very different consequences at stake

Dr Gambhir, a co-author for the study and Senior Research Fellow from Imperial's Grantham Institute - Climate Change and the Environment, said: "We could be on a path to just over 2°C, or just under 3°C, with very different climate consequences in each case."

The Intergovernmental Panel on Climate Change's Sixth Assessment Report on the physical science basis of climate change, published in August this year, stated that every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves, and heavy precipitation, as well as agricultural and ecological droughts in some regions.

Dr Gambhir added: "To date, integrated assessment modelling has overwhelmingly focused on what needs to be done to reach pre-defined temperature targets.

"We, instead, shine a light on where current efforts are taking us, and it reveals a great deal of uncertainty, depending on the modelling approach."

"Predicting emissions in 2030 is difficult enough but extrapolating to 2100 is heroic and requires a good dose of humility to avoid giving false precision." Professor Glen Peters Research Director, CICERO Center for International Climate Research

The researchers also argued that businesses, policymakers and civil society groups were becoming less interested in hypothetical worst-case scenarios that show outcomes for a fossil-fuel dependent future - with little to no policies to reduce the production of greenhouse gases - as such futures are now much less likely.

Instead, attention has turned to what current efforts to combat climate change mean in terms of a warming world, and how stakeholders should plan their actions to further reduce emissions and adapt to the resultant levels of warming accordingly.

It is hoped that the study will inspire more focus on how to model current policy efforts going forward and tackle the challenge of extrapolating policies from 2030 to 2100.

Current efforts may not be enough

Professor Glen Peters, a co-author who also works at CICERO, said: "Most countries have specified policies or pledges to around 2030, but how the implied effort is extrapolated forward through to 2100 is a fundamental uncertainty."

He added: "Predicting emissions in 2030 is difficult enough but extrapolating to 2100 is heroic and requires a good dose of humility to avoid giving false precision."

"The false precision to climate outcomes given during COP26 may lead countries to believe they are making good progress, when the opposite may indeed be the case." Dr Ida Sognnaes Senior Researcher, CICERO Center for International Climate Research

In addition, Dr Sognnaes warned that the large uncertainties in the possible scenarios indicated that more effort may be needed to avoid dangerous global warming outcomes.

She said: "The large uncertainties indicate that current policies and policy pledges can still lead to warming outcomes of 3°C in 2100.

"The false precision to climate outcomes given during COP26 may lead countries to believe they are making good progress, when the opposite may indeed be the case."

"A multi-model analysis of long-term emissions and warming implications of current mitigation efforts" by Ida Sognnaes et al. Published 22 November 2021 in Nature Climate Change.