Emergence of Climate Hazards

Lead Research Organisation: University of Reading
Department Name: National Centre for Atmospheric Science


Climate hazards are weather and climate 'extreme events' that can cause loss of life, injury, or other health impacts, as well as damage and loss to property, infrastructure, livelihoods, service provision, and environmental resources. Examples include:
- The summer heat wave of 2003 in Western Europe, thought to be unprecedented in 500 years, which caused more that 20,000 early deaths, mainly among vulnerable groups in society such as the elderly
- South Asian Monsoon monsoon failures and subsequent agricultural losses - agriculture accounts for 18% of GDP, but employs 60% of people in S. Asia (~1 billion people)
- The extreme El Niño event of 2015/16 that caused floods, droughts and wildfires globally and drove the fastest annual increase in CO2 on record
- A succession of storms reaching southern England in the winter of 2013/2014, causing severe floods and £451 million of insured losses

Such events are, most likely, influenced by global climate change in ways that we do not currently understand. Future climate change may further exacerbate their impacts.

This project will assess the impact of climate change on climate hazards in the past and present and project forward their changes into the future. There is a focus on the next 30 years because of the relevance of this time scale for adaptation strategies produced by governments, businesses and individuals.

EMERGENCE will use information from state-of-the-art climate models, including from models with unprecedented fine detail. It will use cutting edge observations in order to constrain climate model predictions using changes already observed, drawing on new and improved analysis techniques (including event attribution, machine learning and feature tracking) that were not available or not widely applied during previous assessments of climate hazards from older models. The hazards addressed are: extreme heat stress events, tropical deluges and droughts, and storms with their associated extreme winds and rainfall. Information will be integrated into global indicators that will form a snapshot summary of climate hazard risks that, in turn, will be an essential resource for policy makers.

The project's assessments of the emergence of climate hazards will be produced in a timely fashion to feed into the next assessment of the Intergovernmental Panel on Climate Change (IPCC), being relevant to both physical climate science and impacts. The team assembled, including a number of leading climate science project partners from the Met Office, has a strong track record in IPCC and is thus ideally placed to provide this input and to further strengthen the profile of UK climate science in the international arena.

Planned Impact

The research directly addresses a growing need for scientific evidence to inform climate adaptation and resilience-building strategies of national, international and local governments, international development organisations, regulators, business and others.

The impact of this research will be achieved through informing national and international assessments of climate change such as those performed by the Intergovernmental Panel on Climate Change (IPCC) and the UK Climate Projections programme led by the Met Office (principal project partners). It will also provide a set of key indicators and more general briefing material that can be used directly by a broad range of stakeholders in their decision-making.

In the UK, the research directly addresses the agendas of the climate change department of the Department of Business Environment, Innovation and Skills (BEIS), the Department of Food and Rural Affairs (DEFRA) and the Department of International Development (DFID). Internationally, the research addresses the agenda of the United Nations Framework Convention on Climate Change (UNFCCC) and those of many governments world wide, who produce national climate assessments.

The multivariate hazards and compound events vulnerability indicators (WP4), spanning three themes of societal importance: (i) Food security, (ii) Health, (iii) Urban resilience, will feed into IPCC AR6 Working Groups I and II, adaptation aspects of the Global Stocktake and be of relevance for the United Nations Sustainable Development Goals 2, 3, 11 (and hence the Sendai Framework for Disaster Risk Reduction) and 13 (Climate Change).

To ensure maximum impact and relevance to policy, the final work package will be developed with direct engagement of end-users (project partners the Met Office, Public Health England, the Committee on Climate Change the Lancet Countdown, the World Food Programme, and other interested stakeholders) through a co-production method involving a discussion workshop to shape the work programme.
Description Work of Shonk, Turner et al: Greenhouse gas (GHG) and human-induced aerosol emissions have opposing effects on global monsoons, which supply water to billions of people: GHGs strengthen them; aerosols weaken them. This competition has been important in recent decades due to large aerosol emissions and will continue to be important in future until aerosol emissions are reduced. Unfortunately, the effect of aerosols on global climate is very uncertain, leading to a range of temperature and rainfall patterns in model simulations of the last few decades and casting doubt on the magnitude of future climate change. Here, we investigate the effect of this uncertainty on monsoon rainfall using model simulations of the 20th century in which human-induced aerosol emissions are scaled by various factors, the range of which spans uncertainty in present-day aerosol radiative effect. The uncertainty in the effects of human-induced aerosol emissions on global monsoon rainfall is profound. At its weakest, the impact of aerosol is overpowered by GHG and monsoon rainfall increases in the late 20th century. At its strongest, aerosol dominates over GHG, leading to reduced monsoon rainfall, particularly from 1950-1980. Our work emphasises the urgent need to reduce uncertainty in aerosol radiative effects to increase our confidence in future climate projections.

Work of Dosio, Turner et al.: The results of a large ensemble of regional climate models lead to two contrasting but plausible scenarios for the precipitation characteristics over West Africa; one where mean precipitation is projected to decrease significantly over the Gulf of Guinea in spring and the Sahel in summer, and the other one where summer precipitation over both regions is projected to increase. These contrasting scenarios are related to how differently models represent physical processes related to mosisture in the atmosphere and in the soil. Despite the differences, however, some changes in precipitation characteristics are consistent across models. In particular, precipitation frequency is projected to decrease in spring over the Gulf of Guinea and in summer over the Sahel, but precipitation is projected to become more intense.

Work of Huang, Zhou, Turner et al.: The Indian summer monsoon (ISM) rainfall affects a large population in South Asia. Observations show a decline in ISM rainfall from 1950-1999 and a recovery from 1999- 2013. While the decline has been attributed to global warming, aerosol effects, deforestation, and a negative-to-positive phase transition of the Interdecadal Pacific Oscillation (IPO), the cause for the recovery remains largely unclear. Through analyses of a 57-member perturbed-parameter ensemble of model simulations, this study shows that the externally-forced rainfall trend is relatively weak and is overwhelmed by large internal variability during both 1950-1999 and 1999-2013. The IPO is identified as the internal mode that helps modulate the recent decline and recovery of the ISM rainfall. The IPO induces ISM rainfall changes through moisture convergence anomalies associated with an anomalous Walker circulation and meridional tropospheric temperature gradients and the resultant anomalous convection and zonal moisture advection. The negative-to-positive IPO phase transition from 1950-1999 reduces what would have been an externally-forced weak upward rainfall trend of 0.01 mm day- 1 decade-1 to -0.15 mm day-1 decade-1 during that period, while the rainfall trend from 1999-2013 increases from the forced value of 0.42 to 0.68 mm day-1 decade-1 associated with a positive-to-negative IPO phase transition. Such a significant modulation of the historical ISM rainfall trends by the IPO is confirmed by another 100- member ensemble of simulations using perturbed initial conditions. Our findings highlight that the interplay between the effects of external forcing and the IPO needs be considered for climate adaptation and mitigation strategies in South Asia.
Exploitation Route All the findings outlined above will, if accepted in journal publications, will be of direct relevance to authors of the IPCC WGI 6th Assessment Report, which is currently under preparation.
Sectors Agriculture, Food and Drink,Energy,Environment