Attribution of extreme events to climate change

Within the past decade, the attribution of extreme weather events and their impacts has enabled scientists, the public, and policymakers alike to connect real-world experiences of extreme weather events with scientific understanding of anthropogenic climate change. Attribution studies of recent extreme weather events have formed a new and important line of evidence in the most recent Intergovernmental Panel on Climate Change (IPCC) assessment report understanding present-day impacts of climate change. IPCC studies using different methods of event attribution have been assessed together, highlighting that these differences are smaller than the academic discourse on the methods suggests. This development raised two important research questions the science needs to answer: First, how do we formally combine attribution statements using highly conditional methods with probabilistic assessments of how climate change alters the likelihood and intensity of extreme weather events? Second, under what circumstances are individual attribution studies still necessary and to what extent do existing attribution studies provide enough information to answer societal questions? Furthermore, the scientific development still leaves important gaps, particularly in countries of the Global South, leading to ethical questions around the need and requirement of attribution of extreme events in policy contexts, informing adaptation and loss and damage and the role of vulnerability

Harbingers of decades of unnatural disasters

Extreme weather events and their impacts have dominated headlines throughout 2021 and 2022. The emphasis on the weather in reports of the events, often discussed in the context of climate change, has led many to believe that these disasters would not have happened without human-induced warming. However, our compilation of severe weather-related hazards and the most severe related disasters in those two years reveals that ultimately, all the listed disasters resulted from existing vulnerabilities and compounding stresses on social systems. Climate change often made the hazard worse, but much of the damage could have been prevented. We emphasise that the reporting of disasters should routinely address not only the weather-related hazards and humans’ role in changing the odds, but also vulnerability in order to guide disaster risk reduction and avoid risk creation processes

Underestimated climate risks from population ageing

Population ageing is one of the most challenging social and economic issues facing governments in the twenty-first century1. Yet the compounding challenges of people living longer while also coping with the impacts of climate change has been subject to less examination. Here, we show that often-used binary definitions of”vulnerable” older communities – such as people over the age of 65 – can lead to the underestimation of future risks from extreme weather in a warming climate. Within this broad grouping, successively older age groups not only exhibit higher vulnerability to the impacts of climate extremes, but they also show more rapid growth in the future. Lower income countries are more likely to underestimate future climate risks if simplistic classifications of vulnerable older communities persist

Equalising the evidence base for adaptation and loss and damages

Since the UNFCCC Paris Agreement came into force after 2015 international climate policy rests on three pillars: mitigation, adaptation and loss and damage. However, while there are clear agreed-upon metrics to measure emissions, base mitigation goals against and hold countries and companies accountable to, the evidence base for the impacts of climate change to inform adaptation and loss and damage is very different. There are no agreed-upon metrics, nor are there guidelines or criteria to delineate the impacts of climate change from other drivers of losses and damages. This imbalance is reflected in the lack of ability to set and enforce goals. With a new body of scientific evidence introduced in the IPCC, we argue that this can change. Especially with an increasing number of climate litigation cases being recognised as a legitimate root to justice, and thus being given due consideration in courts, the imbalance in evidence could change and put adaptation and loss and damage on more equal footing with mitigation

The role of human-induced climate change in heavy rainfall events such as the one associated with Typhoon Hagibis

Around October 12, 2019, torrential rainfall from Typhoon Hagibis caused large-scale flooding in a large area around the metropole region of Tokyo leading to large-scale destruction including losses of lives, livelihoods, and economic losses of well over $10 bn US dollars. In this paper we use a multi-method probabilistic event attribution framework to assess the role of human-induced climate change in the heavy rainfall event responsible for a large proportion of the damages. Combining different observational datasets and various climate model simulations, we find an increase in the likelihood of such an event to occur of 15–150$4bn of the damages due to the extreme heavy rainfall associated with Typhoon Hagibis are due to human-induced climate change

A real-time Global Warming Index

We propose a simple real-time index of global human-induced warming and assess its robustness to uncertainties in climate forcing and short-term climate fluctuations. This index provides improved scientific context for temperature stabilisation targets and has the potential to decrease the volatility of climate policy. We quantify uncertainties arising from temperature observations, climate radiative forcings, internal variability and the model response. Our index and the associated rate of human-induced warming is compatible with a range of other more sophisticated methods to estimate the human contribution to observed global temperature change

Integrating attribution with adaptation for unprecedented future heatwaves

Citizens in many countries are now experiencing record-smashing heatwaves that were intensified due to anthropogenic climate change. Whether today’s most impactful heatwaves could have occurred in a pre-industrial climate, traditionally a central focus of attribution research, is fast becoming an obsolete question. The next frontier for attribution science is to inform adaptation decision-making in the face of unprecedented future heat

Attribution: how is it relevant for loss and damage policy and practice?

Attribution has become a recurring issue in discussions about Loss and Damage (L&D). In this highly-politicised context, attribution is often associated with responsibility and blame; and linked to debates about liability and compensation. The aim of attribution science, however, is not to establish responsibility, but to further scientific understanding of causal links between elements of the Earth System and society. This research into causality could inform the management of climate-related risks through improved understanding of drivers of relevant hazards, or, more widely, vulnerability and exposure; with potential benefits regardless of political positions on L&D. Experience shows that it is nevertheless difficult to have open discussions about the science in the policy sphere. This is not only a missed opportunity, but also problematic in that it could inhibit understanding of scientific results and uncertainties, potentially leading to policy planning which does not have sufficient scientific evidence to support it. In this chapter, we first explore this dilemma for science-policy dialogue, summarising several years of research into stakeholder perspectives of attribution in the context of L&D. We then aim to provide clarity about the scientific research available, through an overview of research which might contribute evidence about the causal connections between anthropogenic climate change and losses and damages, including climate science, but also other fields which examine other drivers of hazard, exposure, and vulnerability. Finally, we explore potential applications of attribution research, suggesting that an integrated and nuanced approach has potential to inform planning to avert, minimise and address losses and damages. The key messages are In the political context of climate negotiations, questions about whether losses and damages can be attributed to anthropogenic climate change are often linked to issues of responsibility, blame, and liability. Attribution science does not aim to establish responsibility or blame, but rather to investigate drivers of change. Attribution science is advancing rapidly, and has potential to increase understanding of how climate variability and change is influencing slow onset and extreme weather events, and how this interacts with other drivers of risk, including socio-economic drivers, to influence losses and damages. Over time, some uncertainties in the science will be reduced, as the anthropogenic climate change signal becomes stronger, and understanding of climate variability and change develops. However, some uncertainties will not be eliminated. Uncertainty is common in science, and does not prevent useful applications in policy, but might determine which applications are appropriate. It is important to highlight that in attribution studies, the strength of evidence varies substantially between different kinds of slow onset and extreme weather events, and between regions. Policy-makers should not expect the later emergence of conclusive evidence about the influence of climate variability and change on specific incidences of losses and damages; and, in particular, should not expect the strength of evidence to be equal between events, and between countries. Rather than waiting for further confidence in attribution studies, there is potential to start working now to integrate science into policy and practice, to help understand and tackle drivers of losses and damages, informing prevention, recovery, rehabilitation, and transformation

A common framework for approaches to extreme event attribution

The extent to which a given extreme weather or climate event is attributable to anthropogenic climate change is a question of considerable public interest. From a scientific perspective, the question can be framed in various ways, and the answer depends very much on the framing. One such framing is a risk-based approach, which answers the question probabilistically, in terms of a change in likelihood of a class of event similar to the one in question, and natural variability is treated as noise. A rather different framing is a storyline approach, which examines the role of the various factors contributing to the event as it unfolded, including the anomalous aspects of natural variability, and answers the question deterministically. It is argued that these two apparently irreconcilable approaches can be viewed within a common framework, where the most useful level of conditioning will depend on the question being asked and the uncertainties involved