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What is climate change?

The mortality impacts of climate change - part 1 of a 5-part series

Climate Quantified|Insurance Consulting and Technology
Climate and Resilience Hub|Insurer Solutions

February 25, 2021

This paper investigates the liability-side impact of climate change. The first chapter sets the context for our climate risk assessment framework for life insurers by exploring existing climate research and resources which have informed our modelling.

Anthropogenic climate change is one of the greatest challenges facing our planet today. In large part, this will result from significant increases in anthropogenic greenhouse gases (GHG) in the Earth’s atmosphere and oceans that have been accumulating for the last several decades and are expected to continue. The potential future effects of global climate change include more frequent wildfires, longer periods of drought in some regions and an increase in the number, duration and intensity of extreme weather events, melting of glaciers and sea level rise. These will in turn affect water and air quality, taking the form of both sudden and slowly developing factors (Department of Health, 2001; Vardoulakis & and Heaviside, 2012; IPCC, 2013).

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About this Series

This series of articles investigates the liability-side impact of climate change, focusing on the effects on UK life insurers. It considers the mechanisms through which climate can affect mortality, models and quantifies some of those effects and discusses the implications for the life insurance industry.

The extent and timing of climate change effects are subject to a great deal of uncertainty. However, it is generally accepted that they will bring significant risks for human health, life and property (IPCC, 2014). The expected effects on human mortality are the focus of this article. This article does not address other effects of climate change, such as adverse consequences to human health (except to the extent they are directly related to mortality), property damage, and death and reduction in diversity of other living species (for example the bleaching of coral resulting from warmer and more acidic oceans).

Existing climate research and projections

The Intergovernmental Panel on Climate Change (IPCC) was created by the United Nations to provide policymakers with regular scientific assessments on climate change, its implications and potential future risks, and to put forward adaptation and mitigation options. It does not conduct its own research, instead drawing on a team of hundreds of expert scientists to review and synthesise current climate research into assessment reports.

Through its assessments, the IPCC determines the state of knowledge on climate change. It identifies where there is agreement in the scientific community on topics related to climate change, and where further research is needed. IPCC reports are described as neutral, policy-relevant, but not policy-prescriptive. The assessment reports are a key input into the international negotiations to tackle climate change.

IPCC global climate scenarios

The IPCC has developed four scenarios to help climate scientists explore the potential impacts of climate change. These scenarios are called representative concentration pathways (RCPs) and describe different 21st century pathways of GHG emissions, atmospheric concentrations and air pollutant emissions. The RCPs are expressed for future radiative forcing targets in 2100 of 2.6, 4.5, 6.0 and 8.5 watts per square metre (W m-2), and these targets are incorporated into the names of the RCPs; RCP2.6, RCP4.5, RCP6.0 and RCP8.5 pathways.

RCP2.6 is a stringent mitigation scenario that represents a future in which the world aims for and is able to implement sizeable reductions in emissions of greenhouse gases. Many studies show that following this scenario gives a sizeable chance of limiting global average warming to near 2°C above pre-industrial levels, which is also consistent with the long-term target specified in the UK Climate Change Act. Some simulations in the published literature also suggest the RCP2.6 scenario could produce a response as low as the more ambitious target in the Paris climate agreement, which includes provision to aim for limiting warming to below 1.5°C.

RCP8.5 represents a world in which global greenhouse gas emissions continue to rise. It is a potential future where the nations of the world choose not to switch to a low-carbon future. The temperature increases associated with this are much higher than RCP2.6 (see Figure 1). It is important to note that the RCP pathways lead to a broad range of climate outcomes but are neither forecasts nor policy recommendations (Lowe, et al., 2019).

image showing temperature and precipitation changes
Figure 1. Change in average surface temperature (a) and change in average precipitation (b) based on multi-model mean projections for 2081-2100 relative to 1986-2005 under the RCP 2.6 (left) and RCP 8.5 (right) scenarios. Source: IPCC AR5 Synthesis Report: Climate Change 2014

UK climate research

For the United Kingdom, the leading source of climate change information is the United Kingdom Climate Impacts Program’s UK Climate Projections (so-called UKCP18), which is published by the Met Office (Met Office, 2019). Using sophisticated global climate models, UKCP18 projections provide probabilistic representations of monthly, seasonal or annual changes in several climate variables under the four climate scenarios outlined above.

In UKCP18, the projections show a trend towards warmer temperatures throughout the century, with more warming in the summer. The warming is expected to be greatest in the southern UK, but the difference between southern and northern UK warming may not be particularly large. UKCP18 also projects trends for more rainfall in the winter but less rainfall in the summer. For both temperature and rainfall, the changes are much larger if greenhouse gas emissions are assumed to continue to increase (Lowe, et al., 2019).

The marine projections show a continuation and likely acceleration of the sea level rise observed around the UK, and even if emissions are significantly reduced this century the sea level rise will continue well beyond year 2100. Alongside the increases in time-mean sea level there will be increases in extreme coastal water levels, driven mainly by the rise in mean sea level rather than changes in storminess. Changes in tidal characteristics and waves may also occur in the seas around the UK, with increases and decreases both possible, depending on location (Lowe, et al., 2019).

Climate change research and the private sector

Climate change is also increasingly a subject of research by private sector firms and organisations, who are interested in not only potential physical risks, but also risks arising from the green transition and legal liability. Research takes place both through internal projects and innovative public-private partnerships or collaborations.

One of the world’s largest public-private collaborations in the finance sector is the Willis Research Network (WRN). Founded in 2006 by the Willis Group, a legacy organisation of Willis Towers Watson, the WRN has a network of more than sixty organizations in science, academia, think tanks and the private sector working to improve the understanding and quantification of environmental risk, including climate change. The research generated by the WRN is used to support Willis Towers Watson’s Climate and Resilience Hub, the focal point of the firm’s climate expertise and capabilities. The hub pools knowledge from across people, risk and capital businesses to deliver climate and resilience solutions in response to a range of regulatory, investor, consumer, employee and operating pressures.

On 12th November 2020 Willis Towers Watson announced the acquisition of Acclimatise, a leading climate change adaptation advisory and analytics services firm. The Acclimatise team is now part of Willis Towers Watson’s Climate and Resilience Hub. The combination creates a market-leading centre of climate adaptation expertise with over fifty technical staff, significantly expanding the capacity and capabilities of both teams in climate risk assessment, resilience planning and analytics.

Other Willis Towers Watson materials on climate change

Since the early 1990s, Willis Towers Watson (and its legacy organisations) has supported private and public sector organisations around the world to understand the physical, transition and liability risks from climate change, build resilience and capture the opportunities presented by low carbon transition. In that time, Willis Towers Watson has developed a broad range of service offerings, including:

  • Insights into the rapidly evolving policy and investor landscape
  • Risk and scenario modelling using the latest science
  • Climate risk audits and stress testing
  • Risk transfer and financing solutions – broking and insurance product development, reinsurance and insurance-linked securities
  • Asset analysis based on environment, social and governance (ESG) principles and the development of more sustainable, climate resilient portfolios
  • Analytical support for climate-related financial reporting and regulatory requirements
  • Developing talent and reward strategies to support organisational objectives related to climate

The activities of the Willis Research Network, Climate and Resilience Hub, and the Thinking Ahead Institute (TAI) further build knowledge and understanding of climate risks and resilience and are key components of the offering.

For more information on Willis Towers Watson’s strategic response to climate change, read our Insurer Solutions climate risk series.

Next time

In the second chapter, we explore the concept of a driver of mortality and how this can be used in the context of climate risk. A range of climate variables are explored, presenting evidence of the link between these variables and mortality; a short-list of the variables to be used for modelling is developed.

Upcoming chapters

  • Climate variables which can act as drivers of mortality
  • Driver-based modelling
  • Impacts of climate change
  • Implications for life insurers and pension schemes


Department of Health, 2001. Health Effects of Climate Change in the UK, s.l.: Department of Health.
IPCC, 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge: Cambridge University Press.
IPCC, 2014. Climate Change 2014: Synthesis Report. . In: R. Pachauri & L. Meyer, eds. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva, Switzerland: Intergovernmental Panel on Climate Change.
Lowe, J. et al., 2019. UKCP18 science overview report. , Exeter, UK: Met Office Hadley Centre.
Met Office, 2019. Download and view UKCP18 data. [Online] Available at: [Accessed 29 October 2020].
Vardoulakis, S. & and Heaviside, C., 2012. Health effects of climate change in the UK 2012., s.l.: London: Health Protection Agency.

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