The Conversation

Very hot periods will almost certainly lengthen and intensify while extreme weather is likely to increase over the coming century, according to a summary of the Intergovernmental Panel on Climate Change (IPCC)’s forthcoming report, Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, which is due to be released in full in February next year.

Three Australian scientists (Neville Nicholls, John Handmer and Kathleen McInnes) were lead authors among the report’s 220 authors, and Dr McInnes has provided comments below about how climate change is likely to affect Australia, courtesy of the Australian Science Media Centre (AusSMC). Following Dr McInnes' comments is expert analysis of the summary report provided by the Science Media Centre of the UK, and the Science Media Centre of Canada (which also held a “webinar” on the IPCC summary report available here)

Dr Kathleen McInnes, Climate Change Research Group (Sea Level Rise and Coasts), Centre for Australian Weather and Climate Research (a partnership between CSIRO and the Bureau of Meteorology)

Recognising that the effects of climate change will be felt most acutely through extreme events, this report is the first comprehensive assessment that focuses on extreme events as well as bringing together the experience of experts in climate change adaptation and disaster risk management to consider options for managing the risks associated with climate change.

While more regional detail will be available when the full report is released in February next year, some of the findings for Australia are that it is likely that there has been an overall decrease in the number of cold days and nights and an overall increase in the number of warm days and nights. While it is likely that the storm systems that affect southern Australia have moved poleward, changes in observing capabilities means there is low confidence in changes in tropical cyclone activity.

It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale and have led to increasing extreme coastal high water due to mean sea level contributions.

Because of the nature of extremes (i.e. their rarity), changes in many extremes and their causes are assessed with lower levels of confidence due to such factors as length of observational record and the influence of natural variability. However, low confidence in an observed change neither implies nor excludes the possibility that a change has occurred.

It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur through the 21st century and it is very likely that the length, frequency and/or intensity of warm spells, including heat waves, will continue to increase over most land areas. It is also likely that that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in the 21st century over many areas of the globe. In Australia by the end of the 21st Century, a one in 20 year daily maximum temperature is projected to occur once every one to 10 years. It is very likely that mean sea level rise will contribute to upward trends in extreme coastal high water levels in the future.

As well as addressing climate extremes, this report also integrates perspectives from research communities studying adaptation to climate change, and disaster risk management. The severity of the impacts of extreme and non-extreme weather and climate events depends strongly on the level of vulnerability and exposure of human, ecological and physical systems to these events.

Professor Bill McGuire, Professor of Geophysical Climate Hazards, University College London

One of the key ways in which anthropogenic climate change will affect human society is through the increasing impact of extreme events such as floods and droughts. This landmark report uses the latest observations and models to forecast what we will be up against in the decades to come. It also highlights the complex and sometimes unexpected ways in which climate change may drive dangerous extreme events, including a response from the solid Earth in the form of increased landslide activity and other geological hazards.

Dr Simon Brown, Climate Extremes Research Manager, Met Office Hadley Centre

This focus of the IPCC on extremes is very welcome as less emphasis has traditionally been given to these phenomena which are very likely to be the means by which ordinary people first experience climate change. Human susceptibility to weather mainly arises through extreme weather events so it is appropriate that we focus on these which, should they change for the worse, would have wide ranging and significant consequences. This review will be very helpful in progressing the science by bringing together a wide range of studies – not just on the physical weather aspects of climate extremes but also on how we might adapt and respond to their changes in the future.

Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment, London School of Economics and Political Science

This expert review of the latest available scientific evidence clearly shows that climate change is already having an impact in many parts of the world on the frequency, severity and location of extreme weather events, such as heatwaves, droughts and flash floods. This is remarkable because extreme events are rare and it is difficult to detect statistically significant trends in such small sets of data. What is more, these trends have been identified over the last few decades when the rise in global average temperature has been just a few tenths of a centigrade degree. The report shows that if we do not stop the current steep rise in atmospheric levels of greenhouse gases, we will see much more warming and dramatic changes in extreme weather which are likely to overwhelm any attempts human populations might make to adapt to their impacts.

This report should leave governments in no doubt, as they prepare for the next United Nations climate change summit in Durban, South Africa, at the end of November, that climate change is, through its impact on extreme weather, already harming the lives and livelihoods of millions of people around the world. Governments must focus clearly on reaching a strong international agreement to strengthen their efforts to reduce emissions and to prepare their populations for those impacts of climate change that cannot now be avoided.

John Clague, Shrum Research Professor, CRC Chair in Natural Hazard Research, Department of Earth Sciences, Simon Fraser University. Dr. Clague was one of the authors on this IPCC report.

First of all, I think the report does an excellent job in 1) defining terms that are central to the topic and 2) capturing large uncertainties that are inherent and unavoidable when seeking to identify possible trends in climate extremes. Uncertainty is captured by evaluating the evidence for trends (the type, amount, quality, and consistency of the data), as well as the level of agreement among the informed scientific community.

I picked up on several trends that will be important to Canada and that are considered “medium” to “very likely” [these findings are in italics]:

It is very likely that mean sea level rise will contribute to upward trends in extreme coastal high water levels in the future. There is high confidence that locations currently experiencing adverse impacts such as coastal erosion and inundation will continue to do so in the future due to increasing sea levels, all other contributing factors being equal.

Sea level is currently rising at a rate of about 3 mm/yr and the rate is likely to increase through the remainder of the century. Low-lying coastal areas on all three of Canada’s coasts will experience increased erosion and inundation during extreme storms as the century progresses. Erosion and inundation occur during extreme storms, which as noted below, may increase along the Pacific and Atlantic coasts in the future. Greater erosion of some coasts in the Arctic will be exacerbated by reduced Arctic ice cover.

While on this topic, the recent devastating flooding in Bangkok is a harbinger of things to come for that city. Bangkok lies only about 2 m above sea level. The slow rise in sea level reduces the gradient of the Chao Phraya River, which flows through the city to the Gulf of Thailand. During extreme river floods, as occurred this year, the lower ‘freeboard’ to the tops of the protective dykes at high tides increases the likelihood of flooding.

Average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins. It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged.

This is an interesting conclusion – Some hurricanes track up the U.S. Atlantic coast to Nova Scotia (Hurricane Juan) and Newfoundland. An increase in the strength of tropical cyclones may have implications for cities like Halifax, Charlottetown, and St. John’s.

There is medium confidence that there will be a reduction in the number of extra-tropical cyclones averaged over each hemisphere. While there is low confidence in the detailed geographical projections of extra-tropical cyclone activity, there is medium confidence in a projected poleward shift of extra-tropical storm tracks.

Any poleward shift in the tracks of extra-tropical cyclones in the North Pacific might result in an increase in severe storms on the populated south coast of British Columbia. Strong winds resulting from severe storms are perhaps the most damaging natural phenomena in this region.

It is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes and decreases in cold extremes will occur in the 21st century on the global scale. It is very likely that the length, frequency and/or intensity of warm spells, or heat waves, will increase over most land areas. Based on the A1B and A2 emissions scenarios, a 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the 21st century in most regions, except in the high latitudes of the Northern Hemisphere, where it is likely to become a 1-in-5 year event.

Without appropriate planning and remediation, more frequent hot spells, coupled with poor air quality, will increase heat stroke and early death in Toronto, other cities in southern Ontario, and perhaps Montreal.

There is medium confidence that droughts will intensify in the 21st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration. This applies to regions including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa.

A seasonal or multi-annual intensification of drought conditions in the “Palliser Triangle”, in southeast Alberta and southwest Saskatchewan, will reduce grain production and thus adversely impact the Canadian economy. This drought-prone semiarid region is the “bread basket” of Canada. Proxy research on past climates has shown that drought conditions unlike any that have occurred in the past century, including the 1930s “Dust Bowl” era, have happened in the past 1000 years.

There is high confidence that changes in heat waves, glacial retreat and/or permafrost degradation will affect high mountain phenomena such as slope instabilities, movements of mass, and glacial lake outburst floods. There is also high confidence that changes in heavy precipitation will affect landslides in some regions.

Glaciers in British Columbia, Alberta, and the Yukon will continue to retreat. In combination with increased thaw of alpine permafrost, the reduction in glacier cover will result in an increase in landslides and large ‘outburst floods’ from ice-dammed lakes in high mountains. The loss of glacier ice will also impact stream flow, with possible consequences for hydroelectric power production and water use.

Professor Hans Schreier, Aquatic Ecosystem Research Laboratory, Institute for Resources, Environment and Sustainability, University of British Columbia

As a result of the critiques of previous IPCC reports this SREX report is very cautious. The reason for this is two fold; 1. The historic data and records of extreme event is generally poor 2. Land use changes have a significant impact on disasters and most often magnify the impacts

It should be remembered that most of the IPCC efforts and projections are using climate data as a basis and land use information is usually not incorporated into the modelling. I would argue that land use changes alone have likely a greater influence on water processes than climate but they both are changing at the same time. It is therefore impossible to state which is more important. However, what is critical is that the combined effect of extreme event and land use change will have an accelerated impact leading to greater disasters and risks particularly at local levels.

The lack of good historic data is the main reason why many of the experts are cautious in how much confidence they have in the current trends. However, most of the modelled projections to 2100 clearly show an increase in many aspects of extreme events. This means we need to focus on using adaptation and prevention methods to reduce risks. The report mentions that post disaster recovery provides an opportunity to reduce the effect of extreme event. A more appropriate statement would be to use the precautionary principle and start taking steps to reduce the risk of extreme events and prevent or reduce future impacts.

The experts are virtually certain that the frequency and magnitude of daily warm temperature extremes are increasing. The implications of this for food production and energy demands are significant.

They are also confident that the frequency of heavy precipitation and the amount of total precipitation in some regions will produce a much higher risk of flooding when land use changes are taking into consideration. This is of particular concern in urban areas where storm water systems are inadequate. The flooding problem is even more critical in coastal areas because of anticipated sea level rise.

Of particular concern are the Mountain Regions in Canada because are projections show high confidence that changes in heat wave, glacial retreat, permafrost degradation and extreme rainfall events will lead to accelerated sloe instability, landslides and flooding. This will have huge impacts on transportation and tourism and mining activities in mountain area.

Local knowledge needs to be incorporated into the risk assessments and high risk areas need to be identified and measures to reduce these risk should be initiated.

A great Canadian example of a mountain community that has taken the initiative to incorporate climate change and preventative measures in the District of Elkford in B.C. They have incorporated climate change and adaptations into their Official Community Plan. This is the first Canadian community that has taken this initiative and their effort is now highlighted by the UN Framework on Climate Change guidebook.

Professor Patrick M. Condon, James Taylor Chair in Landscape and Liveable Environments, School of Architecture and Landscape Architecture, University of British Columbia

How does the design of cities need to change given that we can expect more frequent and increasingly severe storm events?

Canada must help prevent what is already a disaster from becoming a catastrophe. Vermont and Pakistan are only the latest locations, where rainfall amounts shattered records by huge margins, with resulting damages in the hundreds of billions of dollars. All this present chaos from a mere one degree rise in average global temperatures.

Even if we stopped spewing carbon into the atmosphere tomorrow, global temperatures will rise by 2 degrees Celsius. In this unprecedented circumstance our cities must do two things. First and foremost we must slowly rebuild them so they don’t demand so much carbon to operate. Our cities now demand at least five times more carbon per capita than they did prior to world war two, largely due to our reliance on the car, and the low density sprawl which the car spawned.

Doing our part to slow or stop global warming is not simply a practical imperative; its a moral one. Canadians are responsible for far more than their fair share of climate change. But its major victims live in places like Africa and Bangladesh, where people did very little to deserve this. Our traditions as Canadians demand that we do our share to help. Changing our carbon greedy cities is the place to start.

In rebuilding our cities for an altered world, we must work with our rapidly changing natural systems, not against them. One very simple example: “Green streets”, streets with ample shade trees and natural verges to infiltrate storm water, can both mitigate the threat of floods while naturally cooling our homes. The shade and protection thy provide can also make walking and cycling a more reasonable option than the car.

This “green infrastructure” approach is crucial, not just to help save the planet, but to provide affordable ways to climate-proof our cities. Already we are crushed under the financial burdens of maintaining an infrastructure for storm and flood management that is beyond our capacity to maintain or replace. Now we find that the performance of this expensive system was calculated based on the behaviors of a world that no longer exists. Only through a radical recalibration in conformance with the new uncertainties of an altered planet can we hope to affordably adapt.

Adjunct Research Professor John Stone, Department of Geography, Carleton University. Dr Stone was a member of the Bureau of the IPCC for the 3rd and 4th Assessment Reports

First, I’ve only seen the draft. And that’s important because over the last 5 days or so this report has been discussed with governments in Kampala. The purpose of these talks is to come up with a text that governments can understand, is useful and is in a language that matches the science. So the actual wording in the final document is likely to be different from what I’ve read.

From the draft, I’m not particularly surprised with the findings. It’s pretty much what I expected to see – and it’s a reflection of what’s been known for quite a while. Some of the things (like heat-waves) we have been pretty sure of have not change and some of the things (like hurricanes) still have questions-marks. In the draft report there are some changes to the levels of confidence we can put on the findings. Many of the findings are not much different from those in the IPCC’s 4th report or the one written for US Congress about 4 years ago. The report has addressed how we might respond – including such matters as disaster management. This should be quite useful to governments at all levels.

One thing it [the report] tells us is that heat waves are very likely to increase. This is important for Canada because that puts the health of a lot of people, particularly the elderly, at risk. In Russia there were 40-50,000 additional deaths last year attributable to the heat waves that occurred there. That’s very significant. We expect these heat waves to become more frequent and more intense.

Another variable that this report speaks to is floods. We expect there to be more heavy rain events, which could give rise to more flooding.

When people talk to me these days about climate change it’s often in connection to extreme events and particularly floods. The recent flooding in Thailand was caused by such extreme events, in this case, by tropical cyclones. Extreme rain events are also important for Canada, because they might involve not just rain, they might mean snow or freezing rain.

This is all quite understandable from basic physics: as globe warms it can carry more moisture, which can fall out as increased precipitation.

There is still a lot of controversy with respect to what we know about tropical cyclones – hurricanes in the North Atlantic. There are still some questions about whether there will be increases in hurricanes or not in the future. From what we know, it’s likely that we will see more category 4 or 5 hurricanes – the most intense. The overall number might drop but we may see increases in the number of the stronger ones.

The fact is, we still don’t fully understand them well. One of the factors that sustains hurricanes is the sea surface temperature, which we know is rising. But there are factors that influence hurricane development, such as winds in the upper atmosphere. Hurricanes are rather complicated systems that we still don’t understand entirely. So our confidence in predicting changes is still limited.

The IPCC report, in draft form at least, provides a weaker statement on hurricanes than in the previous report. By weaker, I mean weaker in terms of confidence levels.

From simple statistics and basic physics, we can say that there will be an increase in the frequency and severity of extreme events. What we’ve seen today doesn’t surprise us. It doesn’t mean we can attribute every extreme event to anthropogenic climate change, but it does support the idea that we’ve “loaded the dice,” so to speak. That these extreme events are more likely to happen now than they have been in the past.

With respect to floods, what we do expect to see is an increase in heavy rain events. Flooding is also caused by our changes in stream flow patterns such as when we close off flood plains, straighten rivers, build dams, and similar engineered modifications of river flows. These can exacerbate the flooding that we expect to see. The engineering changes that we’ve introduced into our landscapes confound making firm forecasts. But one of the conclusions we can draw is that because we have modified the climate there could be increases in local flooding.

Most of these extreme events are of a local scale. That’s a problem for science because these extreme events can happen at a scale that is too small for our observing network. Also, modeling such phenomena is difficult because of the challenges of representing small scale processes in the models.

But things have got better. In the past, the reason that we couldn’t say very much about hurricanes was that if they didn’t hit land, they didn’t occur. Now with satellites we have much greater coverage. The situation is also much better now that we have an extensive Doppler radar network. This technology allows us to track all sorts of storms, for example tornadoes. So our ability to track extreme weather has certainly increased. But in terms of providing solid statistics, we need a much longer series of data that isn’t always there.

We can say that the East coast of Canada could be more affected by hurricanes. But it all depends on their tracks, and whether they come on land or stay out at sea.

It’s important to understand that extreme events are not just a meterological phenomenon. They also tend to expose the vulnerabilities in our human socioeconomic structures. For example the New Orleans Hurricane Katrina was not simply an extreme meteorological event. It was also a social and economic catastrophe.

Extreme events are often short lived, but the effects of these extreme events can last a very long time. So it can be very difficult to recover from one extreme event before the next one hits. In developed nations most of the damage is to infrastructure and property and we can put a dollar value on these losses. In developing world it’s often measured in terms of lives lost. You can’t put a dollar value on that.

So extreme events can place a magnifying glass on people and their communities and their infrastructure.

As I have mentioned, from simple statistical and physical arguments we can expect that extreme events will increase and become more damaging. This is because of what we have done to alter our climate. We have in effect loaded the dice. However, the damage caused also has to do with the vulnerability of whatever is impacted. So we have to talk very carefully and we have to be careful in our attribution of cause and effect.

I was an author on the report on extreme events and climate change for the U.S. Congress. In putting together that report there were heated debates about the language that should be used. In the IPCC 4th report – when we came to discussing the summary for policy-makers there was protracted discussion about what we could say. So it will be interesting with this report to see what exact language is used.

Ultimately it’s important to understand that scientific knowledge is not absolute – and our understanding changes over time. That’s part of the scientific process.

One more thought regarding heat waves. There have been some interesting studies on the heat waves but there doesn’t seem yet to be a strong consensus. There are some research papers that are coming out which have said “yes, this is not surprising – the likelihood of these heat waves is actually greater because of climate change.”

I’m going to quote from a study by Stephan Rahmsdorf of the Potsdam Institute for Climate in Germany. He wrote that he “estimates that the local warming trend has increased by five fold the number of records expected in the past decade, which implies an approximately 80% probability that the July 2010 heat wave in Moscow was attributable to anthropogenic climate change. That is quite different from a statement issued by NOAA earlier in the year, which said that the heat waves were mainly due to natural variability.

The caution here is that we are often dealing with different datasets, and different statistical methods. In my view the IPCC gives us the best assessment we’re going to get for the moment.

Matthew Thompson is an editor at The Conversation. This article was originally published on The Conversation – theconversation.edu.au. Reproduced with permission.