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This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.

Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".

Friday, December 2, 2011

Risks of Extreme Events and Disasters: Analysis and Forecast of the IPCC

Summary.  The Intergovernmental Panel on Climate Change (IPCC) recently issued a summary of its forthcoming report “Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation”.  The summary reports that in recent decades the number and severity of extreme weather and extreme climatic events have increased, as determined reliably.  It projects that without imposing world-wide policies intended to reduce greenhouse gas emissions and limit the rise of world-wide temperatures, such events will grow even more.  These include higher extremes of temperature, changes in precipitation patterns including increasingly severe reainfall, drought, and coastal flooding.  The effects on human society around the globe will be significantly impacted, for example in water resources, food security, forestry, health and tourism.

We conclude that the nations of the world should endeavor to reach a new agreement governing greenhouse gas emissions and limiting the extent of the global rise in temperature.

Introduction.  Warming of the long-term average temperature across the globe has been induced by man-made emissions of greenhouse gases into the earth’s atmosphere since the beginning of the industrial revolution, according to the IPCC’s Fourth Assessment Report (4AR)).  4AR indicated that there was a strong likelihood that warmer temperatures across the globe could lead to periods of high temperature experienced as heat waves; increased aridity, including drought; and  higher precipitation, perhaps coupled with storms of higher intensity and river flooding; among others. 

A previous post on this blog reviewed two scientific publications that for the first time explicitly linked extremes of rainfall and flooding through the year 2000 to the warming of the average global temperature as a result of greenhouse gas emissions.  Statistical analyses of rainfall and flooding were used to correlate observed rainfall patterns or flooding resulting from heavy rains to the predictions of several climate models that include the increased concentration of greenhouse gases in the atmosphere.  The linkage between the greenhouse gases and the extreme rainfall and flooding established the role of mankind’s burning of fossil fuels in the phenomena analyzed with certainty.

On November 18, 2011 the IPCC released a “Summary for Policy Makers of its Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation” [Field, C. B., Barros, V., Stocker, T.F., Qin, D., Dokken, D., Ebi, K.L., Mastrandrea, M. D., Mach, K. J., Plattner, G.-K., Allen, S. K., Tignor, M. and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA (SREX)).  (The complete report is due in February 2012.)  This post presents a selection of the main findings presented in SREX.

Special Report on Extreme Events.  SREX, using previously published data and reports, including AR4, examined the intersection of long-term changes in climate, the degree of exposure of populations and socioeconomic groups to extreme events, and the susceptibility of these exposed entities to actual damages arising from the climate changes, using methods of statistical analysis.  The report excludes discussion of possible programs for mitigation of greenhouse gas emissions and the extent of warming of the climate.

Historical Climate Data

SREX outlines several conclusions concerning changes in climate-driven extremes and in their impact on human activities.  It uses a coded italicized  indication of likelihood or confidence level in a given statement, which is indicated here as needed.

The Report concludes that, compared with the period 1981-2000, it is very likely (90-100% probability) that the number of cold days and nights has decreased worldwide, and that the number of warm days and nights has increased. 

Where available, adequacy of and agreement of data indicate that the length and or number of heat waves has increased.  It is likely (66-100% probability) that many regions across the globe have had an increased number of heavy precipitation events.

It is likely that man-made effects on climate, including increasing concentrations of greenhouse gases, have contributed to warming of extreme daily temperatures.

Data concerning river floods is limited and superimposed on changes in land use and engineering projects. Increases in extreme precipitation across the globe are linked to man-made climate contributions with medium confidence.  It is likely, however, that coastal high water extremes have increased, related to a higher mean sea level. It is likely that man-made climate contributions have led to increases in extreme coastal high water.

Modeled Future Climate Likelihoods

SREX concludes that, compared with the period 1981-2000, the frequency of unusually hot days will increase and the frequency of unusually cold days will decrease, considerably by the period 2045-2065, and greatly by the period 2081-2100, with a probability of 99-100%.  As well, the frequency of unusually heavy precipitation will increase, with a probability of 66-100%.  A baseline for an “unusually hot day” and “unusually heavy precipitation” refers to events that on a broad scale occurred about every 20 years during 1981-2000. 

SREX presents a diagrammatic world map with 26 regions of land surface identified.  For each region there is a graphical diagram showing how the interval between such unusual events is predicted to shorten, based on the results of climate modeling using three different scenarios (see Details below) and twelve climate models of greenhouse gas accumulation in the atmosphere.  In addition, a global average of interval shortening is presented for hot days and for precipitation events; these are given in the following graphic (please read the explanatory legend):

Reduction in the interval between (increased frequency of) events predicted by global climate models, using Scenarios B1, A1B and A2 for future emissions of greenhouse gases.  A: Bottom, diagram showing that for the barred image for each scenario, the median value obtained from all the models used is the heavy horizontal line, the highly likely range of values (central 50% of the range obtained from the various climate models used) is shown by the vertical shaded box, and the full range of values obtained from all the models is shown by the extent of the upper and lower bars.  Top, a hypothetical depiction of results permitting interpretation of the actual results in B and C.  Violet boxes and bars, Scenario B1; Green boxes and bars, Scenario A1B, and Orange boxes and bars, Scenario A2.  The vertical axis showing years predicted between unusual events (the inverse of frequency) is logarithmic, not linear.  The left set of three boxes and bars is the prediction for the period 2046-2065, and the right set is for the period 2081-2100.  B. Reduction in land-based globe-wide years predicted between unusual hot days.  C. Reduction in land-based globe-wide years predicted between heavy precipitation events.

(Please link here to see the regional diagrams, which have the same format as the graphic above.)

SREX foresees with medium confidence that droughts will become more severe as this century progresses in regions such as southern and central Europe, central North America and northern Central America, and southern Africa.

It is very likely that the mean sea level will continue rising during the 21st century, leading to the prediction with high confidence that locations experiencing coastal erosion and ocean flooding will continue to be affected.

Harms and Damages from Climate Disasters

In recent months this blog has posted estimates of damage from extremes of climate (Extreme Wildfire Events and Global Warming, and Economic Costs of Extreme Weather Events Due to Global Warming) and a nationwide estimate of damages in the U. S. (Estimated Costs of U.S. Extreme Weather Events).

SREX finds that financial losses from climate related disasters have increased, albeit with considerable variation in amount and location, in the years from 1980 to 2010 (see the graphic below).  The highest spike, at about US$ 225 billion, includes the damage from Hurricane Katrina in 2005, in the U. S.

Yearly losses for 1980-2010 from climate-related disasters in billions of U. S. dollars at 2010 values.  Orange, full extent of losses; blue, portion covered by insurance.

Future damages and losses due at least in part to effects of the warming climate are expected in water resources, food security, forestry, health and tourism.  Generally infrastructure also will be affected, although the report finds it difficult to project effects because specific effects arising from demographic patterns and economic well-being vary greatly from region to region.


SREX presents summaries of historical climate patterns, and extreme weather and climate events associated with them.  It projects future trends in such events using climate models, concluding that their number and severity will increase during the rest of this century.  Statistical methods were used to assess the likelihood and/or the degree of confidence in the predictions.

SREX is but one of many analyses of future trends in greenhouse gas emission, the extent of global warming and its effects on extreme events, human wellbeing, and economic activity that have appeared in recent years.  Some have been summarized in earlier posts in this blog.  As has been pointed out, in the absence of actions taken to reduce greenhouse gas emissions and limit the rise of the long-term global average temperature, we will experience more frequent severe climate effects.

The nations of the world, parties to the U. N. Framework Convention on Climate Change, are currently meeting in Durban, South Africa (see here and here) for negotiations on a binding climate agreement.  In face of evidence such as that summarized here, it is imperative that they overcome their fundamental differences and conclude a new treaty limiting greenhouse gas emission, the rise of the world climate’s temperature, and the damages arising from warming.  Since the atmosphere bathes the entire planet, all nations owe it to themselves and all others to persevere in this endeavor.


None of the three scenarios used in SREX includes additional climate policy actions that would reduce greenhouse gas emissions or reduce global warming.

The B1 scenario describes a world population that peaks in mid-21st century and then declines, and an economy moving toward a service economy and an information technology base.  It demands lower reliance on materials and energy sources.

The A1B scenario describes a world population that likewise peaks in mid-century then declines.  There is rapid development of new efficient technologies and rapid reduction in income disparities among regions of the planet.  Energy sources in A1B represent a balance between fossil fuels and non-fossil energy sources.

The A2 scenario contrasts with those above by having regions of the world develop relatively independently.  The population continues to expand.  Economic development proceeds regionally rather than integrated globally.

The predicted CO2 emissions for the three scenarios increase by 2100 in the order B1, A1B, A2.  The distinctions in emissions between them are quite pronounced by 2100.

© 2011 Henry Auer

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