The report looks at the evidence for each extreme weather event and gives an assessment of probability and confidence value of each weather event assessment and the future trend. It involved some 220 expert authors from 62 countries and involved more than 18,000 review comments.
Qin Dahe, Co-chair of IPCC Working Group I, which together with Working Group II was responsible for the development and preparation of the report, said: "There is high confidence that both maximum and minimum daily temperatures have increased on a global scale due to the increase of greenhouse gases. Changes in other extremes, such as more intense and longer droughts are observed in some regions, but the assessment assigns medium confidence due to a lack of direct observations and a lack of agreement in the available scientific studies. Confidence in any long-term trend in tropical cyclone intensity, frequency or duration is assessed to be low," he added.
On future trends Thomas Stocker the other Co-chair of Working Group I, said "For the high emissions scenario, it is likely that the frequency of hot days will increase by a factor of 10 in most regions of the world. Likewise, heavy precipitation will occur more often, and the wind speed of tropical cyclones will increase while their number will likely remain constant or decrease".
A lead author of the report was Australian scientist, Dr Kathleen McInnes from the Climate Change Research Group (Sea Level Rise and Coasts) at the Centre for Australian Weather and Climate Research, a partnership between CSIRO and the Bureau of Meteorology. Kathleen McInnes said : "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."
"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 1 in 20 year daily maximum temperature is projected to occur once every 1 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."
Dr McInnes also highlighted the importance in the report of integrating disaster risk management with devising climate adaptation strategies, "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."
The Australian Climate Change Minister, Greg Combet pointed out that Australia is projected to experience large scale increases in the number of days over 35°C and 40°C and an increase in heatwave duration. In comenting on the report he said "Australians are well acquainted with the devastating impacts of extreme events. In the past two years, much of the eastern states have been significantly impacted by events including heatwaves, bushfires, extreme flooding and cyclones," said Mr Combet. "The Government is working to reduce the severity of these impacts by reducing our carbon pollution as part of international efforts to tackle climate change, and adapting to the impacts that cannot be avoided,"
Leader of the Opposition, Tony Abbott, commented on the report in a doorstop interview: "I think it's interesting that the Intergovernmental Panel on Climate Change is seemingly less dogmatic now than it has in the past but this debate is not about the science of climate change, it's about how we best deal with it." and then followed with an attack on the Government's carbon pricing legislation.
Extreme weather event trends and assessment
* Temperatures and Heatwaves : The report confirms that it is very likely that temperatures have increased with an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, on the global scale. There is medium confidence that the length or number of warm spells and heat waves has also increased.
* Precipitation, storms, hurricanes. There have been more heavy precipitation events in some regions. It is likely that more of these regions have experienced increases than decreases, although there is substantial variation in regional trends. The report assesses a low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity, including intensity, frequency, and duration. However extra-tropical storm tracks are likely to have made a poleward shift in both Hemispheres. tornadoes and hail event trends have been given a low confidence.
* Droughts - medium confidence of more intense and longer droughts in some regions, particularly in southern Europe and West Africa. Some regions droughts have become less frequent, less intense, or shorter, e.g., in central North America and northwestern Australia.
* Floods - as the evidence is limited of the magnitude and frequency of floods at regional scales and with changing land use and engineering also confounding data, there is low confidence at the global scale of this evidence.
* Sea Level - "It is likely that there has been an increase in extreme coastal high water related to increases in mean sea level."
The report judges "There is evidence that some extremes have changed as a result of anthropogenic influences, including increases in atmospheric concentrations of greenhouse gases. It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures on the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation on the global scale. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water due to increase in mean sea level."
For tropical cyclone activity the report makes clear there are still too many uncertainties for attribution of a single cyclonic event to human causation. "The uncertainties in the historical tropical cyclone records, the incomplete understanding of the physical mechanisms linking tropical cyclone metrics to climate change, and the degree of tropical cyclone variability provide only low confidence for the attribution of any detectable changes in tropical cyclone activity to anthropogenic influences."
A few years ago it was impossible to say any single extreme weather event was caused in part by anthropogenic influences. But that is no longer the case. Some extreme weather events where there is good historical data and accurate regional modelling can be assessed for attribution to anthropogenic climate change, but the work is still very challenging. The European heatwave of 2003, the floods in England and Wales in 2000 and Russian heatwave of 2010 have all been assessed as being caused at least in part by anthropogenic climate change through statistical modelling of probabilities and fractional attributable risk studies.
Economic losses from weather- and climate-related disasters have increased, but this is also a reflection of increased asset value in Western and developing countries. Many more lives are lost in poor and developing countries where their is greater vulnerability and exposure to weather extremes. From 1970-2008, over 95% of natural-disaster-related deaths occurred in developing countries
The impacts of climate extremes depends upon the exposure and vulnerability of populations. Where there is good infrastructure and disaster risk management, exposure and vulnerability will be much lower.
The human activities which will be most impacted by extreme weather events include use of water, agriculture and food security, forestry, health, and tourism.
* Temperatures - "Models project substantial warming in temperature extremes by the end of the 21st century. 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."
* Precipitation - "It is likely 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. This is particularly the case in the high latitudes and tropical regions, and in winter in the northern mid-latitudes. Heavy rainfalls associated with tropical cyclones are likely to increase with continued warming. There is medium confidence that, in some regions, increases in heavy precipitation will occur despite projected decreases of total precipitation in those regions."
* Tropical Cyclones - Intensity may increase but frequency may stay the same or even decrease. Wind speeds likely to increase, although perhaps not in all ocean basins. Medium confidence in a projected poleward shift of extra-tropical storm tracks, and a reduction in the average number of extra-tropical cyclones.
* Droughts - "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."
* Sea Level Rise - "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. The very likely contribution of mean sea level rise to increased extreme coastal high water levels, coupled with the likely increase in tropical cyclone maximum wind speed, is a specific issue for tropical small island states."
* Mountain regions - "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."
* Floods - the report acknowledges that precipitation and temperature changes imply changes in floods but there is low confidence in projections, with limited evidence and complex regional land use changes occurring. However, "There is medium confidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases in local flooding, in some catchments or regions."
* Monsoons - "Confidence is low in projections of changes in monsoons (rainfall, circulation)"
* El Nino Southern Oscillation (ENSO) - "low confidence in projections of changes in this phenomenon"
Figure SPM.5: Projected annual changes in dryness assessed from two indices. Left column: Change in annual maximum number of consecutive dry days (CDD, days with precipitation <1 mm). Right column: Changes in soil moisture (soil moisture anomalies, SMA). Increased dryness is indicated with yellow to red colors; decreased dryness with green to blue. Projected
changes are expressed in units of standard deviation of the interannual variability in the three 20-year periods 1980-1999, 2046-2065 and 2081-2100. The figures show changes for two time horizons, 2046-2065 and 2081-2100, as compared to late-20th-century values (1980-1999), based on GCM simulations under emissions scenario SRES A2 relative to corresponding
simulations for the late-20th-century. Results are based on 17 (CDD) and 15 (SMA) GCMs contributing to the CMIP3. Colored shading is applied for areas where at least 66% (12 out of 17 for CDD, 10 out of 15 for SMA) of the models agree in the sign of the change; stippling is added for regions where at least 90% (16 out of 17 for CDD, 14 out of 15 for SMA) of all models agree in the sign of the change. Grey shading indicates where there is insufficient model agreement (<66%).
Disaster Risk management and Climate adaptation
There are many measures that can be taken to reduce the risk in projected trends and range of climate scenarios. 'Low regrets measures' have the ability to alter the exposure, vulnerability, and improve the resilience of people and structures facing extreme weather events. These measures can also provide other benefits such as improving livelihoods, human well being, and biodiversity conservation.
The measures might include adoption of early warning systems and better forecasting of extreme weather events, risk communication between decision makers and local populations, improved land use planning, improved ecoystem management and restoration, better health response initiatives, sanitation, drainage, and improved building codes.
There is an important part to play for local people integrating their local knowledge in hazard reduction and risk management. "Integration of local knowledge with additional scientific and technical knowledge can improve disaster risk reduction and climate change adaptation (high agreement, robust evidence)." says the report.
Timely communication of risks, even of the extent of uncertainty and complexity involved in an extreme weather event is critical for people to use appropriate adaptive strategies and disaster risk management. And of course our disaster risk management strategies, whether used on a personal or community level, should be examined after each event to improve their ongoing effectiveness.
We need to implement a range of actions from small incremental steps individuals and local communities can easily implement to major transformational changes that might entail changes to how we make decisions, our value systems, or technological system.
Climate adaptation will involve many approaches and pathways to implementing a sustainable and resilient future. But in some places and circirmstances adaptation may be beyond people's capacity, espcially if mitagation action is deferred and greenhouse gases continue to increase in the atmosphere. There was a record increase in greenhouse gas emissions in 2010 to the atmosphere.
"...limits to resilience are faced when thresholds or tipping points associated with social and/or natural systems are exceeded, posing severe challenges to adaptation." says the report.
The report was commissioned at the 29th Session of the IPCC held in Geneva, Switzerland in September 2008. It was agreed that Working Groups I and II would jointly prepare a Special Report on Managing the Risks of Extreme Events and Disasters (SREX). The Summary for Policymakers of the SREX was approved by the First Joint Session of IPCC Working Groups I and II in Kampala, Uganda, 14-17 November 2011 and was launched on 18 November. The full report will not be available until February 2012.
Hans Schreier, Professor, Aquatic Ecosystem Research Laboratory, Institute for Resources, Environment and Sustainability, University of British Columbia, observed that this SREX report is very cautious as a result of previous critiques of the IPCC process. He contends that the reasons it is so cautious are that the historic data and records of extreme events is generally poor and 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." said Professor Hans Schreier.
Figure: IPCC Assessment Reports: The Process - last slide in presentation slide pack showing the careful and convoluted process for generating a report like SREX.
Patrick M. Condon, Professor & James Taylor Chair in Landscape and Liveable Environments, School of Architecture and Landscape Architecture, University of British Columbia said that we need to change the design and operation of our cities. "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."
"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." said Professor Condon.
"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." said Condon.
Bob Ward, policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science, offered the following comment on the report via the UK Science Media Centre:
"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." concluded Bob Ward.
- IPCC SREX Summary for Policymakers, IPCC Media Release, Kampala, 18 November 2011 available from IPCC SREX Report website
- Comments from the Science Media Centre of Canada , Science Media Centre in the UK, and Australian Science Media Centre
- Media releases and media reports of comments by Greg Combet and Tony Abbott
- Images from the report and associated documentation