Professor Nigel Arnell, Director of the Walker Institute, University of Reading, was a lead author on one of the chapters of the IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation.
The summary for the latest IPCC report on climate change and extreme events was published on 18 November, following a meeting in Kampala, Uganda. This new IPCC report represents the culmination of three years of activity by physical and social scientists, and marks the most comprehensive attempt so far to summarise the past and potential future effects of climate change on the risks of extreme events and disasters.
Professor Arnell said: “There’s strong evidence from today’s IPCC report that human influence on climate is increasing the risks from some extreme events and that risks from heat waves, droughts and heavy rainfall are set to rise through the 21st century. Whether you’re an insurance company or a farmer in Africa, you can’t manage the risks from climate effectively without factoring in the effect that people are having.
“Of course we can’t assume that all changes in extreme events are due to greenhouse gases. Natural forces like the periodic El Nino/La Nina events in the tropical Pacific have profound effects on extreme events around the world. We have to take account of natural variations in climate and the changes that people are causing. And of course the impacts of future extreme events will depend on the future changes in social and economic exposure to loss.
“We are seeing more hot days, less cold days, more heavy rainfall events and higher coastal water levels and this is probably as a result of increasing greenhouse gases. As greenhouse gases rise through the 21st century, so the risks will rise.
“More heavy rainfall events could lead to an increased risk of inland flooding in many areas, but the link is complicated by things like changing river flood defences, human interventions in catchments, and of course a strong trend towards increasing exposure to loss so it is difficult to estimate the magnitude of future impacts. At the other extreme, we are quite confident that lower seasonal rainfall and higher temperatures will increase the frequency of droughts in and around the Mediterranean and a few other regions.”
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Climate change: interesting stats
- Global temperatures have risen by three quarters of a degree centigrade over the 20th century. As temperatures rise more over the 21st century we can expect such extreme events to become more severe and more frequent.
- Climate models show that without action to reduce greenhouse gas emissions, global temperatures could rise by 1.5 to 4 degrees C by 2100.
- In London, the 1 in 100 year maximum temperature is currently around 36 degrees C. By the 2050s the 1 in 100 year temperature could be around 40 degrees C.
- There is growing evidence to show that human-induced climate change is affecting day to day weather. For example, scientists have looked at the UK flooding in autumn 2000, the wettest autumn since records began in 1766, and found that the risks of such an event have increased as a result of human induced climate change.
Research at the University of Reading’s Walker Institute is improving understanding of how both natural and human induced changes are affecting climate to improve predictions of climate over coming seasons and decades.
For example, the Walker Institute is working with the Queensland government to look at floods and droughts. The flooding over eastern Australia in December 2010/January 2011 was linked to a strong cool La Nina event in the tropical Pacific. To try and understand what might happen to Australian rainfall in the future we are looking at natural variations like La Nina/El Nino as well as the effect that increasing greenhouse gases might have.
The Walker Institute has been working with Willis Re to investigate climate risk and its impact on the insurance industry and the global population it serves. Powerful high resolution climate models are being applied to understand the risks from tropical cyclones, and other weather related hazards, and to assess how risks might change in the future.
Walker Institute scientists have shown that intense tropical rainstorms increase in a warmer climate. We see this in both observations and simulations of past rainfall and in predictions of future climate. Climate models appear to underestimate the observed increase in rainfall intensity, so predictions of future changes in extreme rainfall could be underestimated.
Our research also suggests that the summer monsoon rains over India could come in shorter, heavier bursts with longer dry periods in between. The result may be both increased flooding and, paradoxically, increased drought.
The Walker Institute is working with Deloitte to look at heat waves and very hot days. For example, over London, the 1 in 100 year maximum temperature is currently around 36 degrees C. By the 2050s the 1 in 100 year temperature could be around 40 degrees C.
The Walker Institute, with the National Centre for Atmospheric Science, is developing more detailed climate models which can better represent things like storms and heat waves. Extreme weather typically comes from quite small scale weather systems, such as the low pressure systems that bring rain to the UK. To improve predictions of extreme weather, we need climate models that can more accurately simulate the systems that bring extreme weather.