A new report from some of the world's most eminent scientists is warning that exposure of human populations to extreme weather is set to increase hugely as global climate and population size, location and age continue to change.

The Royal Society report Resilience to extreme weather says extreme weather has a huge human cost that cannot be quantified, pointing out that between 1980 and 2004 the economic cost has been estimated to be US$1.4 trillion.

The authors say this shows that societies are not resilient to extreme weather today and that their analysis shows that the risk it poses is increasing. They estimate the risk to individuals from floods will rise more than four-fold and the drought risk will treble.

"Average global flood losses could increase to US$1 trillion p.a."

The scenarios in the report are based on the assumption that the world stays on the current trajectory of emissions, which the authors assume will increase temperature by 2.6-4.8C around 2090, together with an assumed global population of nine billion. The report warns that in the worst case average global flood losses could increase to US$1 trillion or more per year by 2050, up from US$6 billion per year in 2005. Even if emission rates are reduced, societies will still need to adapt to climatic changes caused by past emissions - both mitigation of climate change and adaptation are therefore vital.

The scientists are calling for steps to be taken immediately to reduce people’s exposure and vulnerability both now and in the future, identifying Governments as the main bodies with the resources, oversight and powers to do this.

The report says the risks from climate change can be underestimated if no account is taken of people’s exposure and vulnerability  - with risks associated with extremes set to increase in areas of the world that are densely populated.

In general, wet regions are likely to get wetter under climate change whilst dry regions become dryer, meaning that areas currently struggling with floods and droughts might expect these challenges to become increasingly severe. Urbanisation can also exacerbate extreme weather – for example, raising flood risk by increasing runoff concentration.

The report compares the different physical approaches to reduce the impact of four weather-related hazards – coastal flooding, river flooding, heatwaves and droughts. The analysis suggests that a portfolio of defensive options to address a range of hazards, involving both physical and social techniques, will be most effective.

Need to look beyond traditional engineering options to those based on natural ecosystems 

It also suggests that those investing in infrastructure to reduce the impact of extreme weather should look beyond traditional engineering options to those based on natural ecosystems or processes, commenting:

“ There is evidence that options which incorporate these ecosystem-based approaches are more affordable and deliver wider societal benefits as well as reducing the immediate impact of the hazard. However, more evidence is needed to monitor their effectiveness and inform future decisions.”

The report says Governments should develop and implement resilience strategies and incorporate resilience-building into other policies which should then be evaluated and updated on an ongoing basis in the light of new evidence. It also says that if international organisations and national governments directed more funds to resilience-building, the need for costly disaster responses would be reduced.

Focus should be on minimising infrastructure failure rather than complete avoidance

Governments have a responsibility to develop and resource resilience strategies and will be most effective when they:

• focus on minimising the consequences of infrastructure failure rather than avoiding failure completely - for example by prioritising the resilience of critical infrastructure and having plans to minimise impacts when non-critical infrastructure fails;
• incorporate resilience-building into other relevant policies such as poverty alleviation and land-use planning;
• consider all the factors – the whole system – likely to be impacted by extreme weather, including geographical areas beyond those directly affected, and effects over decades;
• use a range of expertise from disciplines such as environmental management, climate change adaptation, disaster risk reduction and sustainable development.

More funding needed and risks should be addressed in wider global financial system

It suggests that at the international level, governments will be more effective when they act together to build resilience - sharing expertise, co-ordinating policy and pooling resources to confront common risks. To limit the need for costly disaster responses, more national and international funds will need to be directed to measures that build resilience to extreme weather.

The risks posed by extreme weather also now need to be better accounted for in the wider financial system, in order to inform valuations and investment decisions and to incentivise organisations to reduce their exposure. This could be done through a requirement for public and private sector organisations to report their financial exposure to extreme weather at a minimum of 1 in 100 (1%) per year risk levels.

The report says that policy-makers need to take practical measures to protect people and their assets from extreme weather which will be most effective when they:

• address multiple hazards and use a portfolio of defensive options;
• consider defensive options beyond traditional engineering approaches – for example, ecosystembased and hybrid approaches that offer additional benefits to people – and consider the value of conserving existing natural ecosystems that are difficult or impossible to restore; and
• monitor and evaluate the effectiveness of interventions, in particular of more novel approaches such as ecosystem-based ones, and apply the results to improve future decision-making.

The report also points out that in 2015 important international agreements will be reached on disaster risk reduction, sustainable development and climate change. The authors say the agreements will be much more effective in addressing extreme weather and its impacts if their purpose, design and implementation is aligned, and if they are informed by robust evidence. They say their report will help those negotiating and implementing the new agreements to decide what action to take to most effectively build resilience.

UK Chancellor must invest seriously in flood defence in Autumn Statement

Reacting to the report, Friends of the Earth climate campaigner Guy Shrubsole said:

 "As the anniversary of Britain's wettest winter ever approaches, this Royal Society report is a timely wake-up call for politicians to get serious about protecting the country from climate change.”

 "The Chancellor must use next week’s Autumn Statement to invest seriously in flood defence schemes to protect hundreds of thousands of UK households and businesses increasingly at risk from extreme weather.”

 Click here to download the full report