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Working Group II Definitions

Likelihood of an outcome or result
Virtually certain > 99% probability of occurrence
Extremely likely > 95%
Very likely > 90%
Likely > 66%
More likely than not > 50%
Very unlikely < 10%
Extremely unlikely < 5%.

Confidence in a statement
Very high confidence: At least a 9 out of 10 chance of being correct
High confidence: About an 8 out of 10 chance
Medium confidence: About a 5 out of 10 chance
Low confidence: About a 2 out of 10 chance
Very low confidence: Less than a 1 out of 10 chance

Confidence symbols in the text
*** Very high confidence
** High confidence
* Medium confidence

Key Assumptions

The Working Group II report discusses future impacts "for the range of unmitigated climate changes projected by the IPCC over this century judged to be relevant for people and the environment." Its different scenarios of future emissions of greenhouse gases "do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol."

Hurricanes and Sea Level Rise
Key passages from the IPCC's "Climate Change 2007"

The IPCC's "Climate Change 2007: The Physical Science Basis"
Issued Feb. 2

Key passages from report released April 6 (Impacts)
Key passages from report released April 16 (Mitigation)
Key passages from report released November 17th (Synthesis)

Key passages from the report by the IPCC's Working Group I:


Observed changes
"There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures.... There is no clear trend in the annual numbers of tropical cyclones."

"Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical SSTs (sea surface temperatures). There is less confidence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period."


Observed changes
"Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m (9,843 feet) and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise."

"Warming of the climate system has been detected in changes of surface and atmospheric temperatures, temperatures in the upper several hundred metres of the ocean and in contributions to sea level rise. Attribution studies have established anthropogenic contributions to all of these changes."

"There is high confidence that the rate of observed sea level rise increased from the 19th to the 20th century. The total 20th century rise is estimated to be 0.17 m (0.56 feet)."

Human causation
"Anthropogenic forcing is likely to have contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns in both hemispheres." (In IPCC terminology, "likely" means a probability greater than 66 percent.)

"Contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100."

"Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the timescales required for removal of this gas from the atmosphere."

The report gives no "best estimates" for projected sea level rise. For six emissions scenarios, it provides six projected ranges, extending from 0.18 meters (0.59 feet) to 0.59 meters (1.94 feet) between 1980-1999 and 2090-2099.

The 2007 Working Group I report narrows and slightly lowers the range of IPCC projections for sea level rise (established in the Third Assessment Report issued in 2001), but the report also dramatically increases the uncertainty about the upper range of these projections.

"Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003,but these flow rates could increase or decrease in the future. For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES (emission) scenarios shown in Table SPM-3 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise."

"Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude."

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"Climate Change 2007: Impacts, Adaptation and Vulnerability"
Issued April 6

Key passages:

"The most vulnerable industries, settlements and societies are generally those in coastal and river flood plains, those whose economies are closely linked with climate-sensitive resources, and those in areas prone to extreme weather events, especially where rapid urbanisation is occurring [high confidence]."

"Very large sea-level rises that would result from widespread deglaciation of Greenland and West Antarctic ice sheets imply major changes in coastlines and ecosystems, and inundation of low-lying areas, with greatest effects in river deltas. Relocating populations, economic activity, and infrastructure would be costly and challenging. There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1- 4°C (relative to 1990-2000), causing a contribution to sea level rise of 4-6 m or more. The complete melting of the Greenland ice sheet and the West Antarctic ice sheet would lead to a contribution to sea-level rise of up to 7 m and about 5 m, respectively."

[From the report's North America section:]

"Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with development and pollution. Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low [very high confidence]."

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North America Chapter of the IPCC's WGII Technical Report:
"Climate Change 2007: Impacts, Adaptation and Vulnerability"

Issued April 16

Key Passages:

"The devastating effects of hurricanes Ivan in 2004 and Katrina, Rita, and Wilma in 2005 . illustrate the vulnerability of North American infrastructure and urban systems that were either not designed or maintained to adequate safety margins."

"North America very likely will continue to suffer serious losses of life and property simply due to growth in property values and numbers of people at risk (very high confidence). Of the US $19 trillion value of all insured residential and commercial property in the U.S. states exposed to North Atlantic hurricanes, US $7.2 trillion (41%) is located in coastal counties. This economic value includes 79% of the property in Florida, 63% of the property in New York, and 61% of the property in Connecticut."

"The impacts of hurricanes Katrina, Rita, and Wilma in 2005 and Ivan in 2004 demonstrated that the Gulf of Mexico offshore oil and natural gas platforms and pipelines, petroleum refineries, and supporting infrastructure can be seriously harmed by major hurricanes which can produce national level impacts, and require recovery times stretching to months or longer."

"The poor and marginalized in Canada and the U.S. have historically been most at risk from weather shocks, with vulnerability directly related to income inequality. Differences in individual capacity to cope with extreme weather were evident in New Orleans during and after Hurricane Katrina, when the large majority of those requiring evacuation assistance were either poor or in groups with limited mobility - including elderly, hospitalized, and disabled citizens."

"Extensive property damage in Florida during Hurricane Andrew in 1992 led to significant revisions to the building code. If all properties in southern Florida met this updated code in 1992, then property damage from Hurricane Andrew would have been lower by nearly 45%. Florida will, however, still experience extensive damage from hurricanes through damage to the large number of older homes and businesses. Other financial barriers come from the challenge property owners face in recovering the costs of protecting themselves. Hidden adaptations tend to be undervalued, relative to obvious ones. For example, homes with storm shutters sell for more than homes without this visible adaptation, while less visible retrofits, such as tie-down straps to hold the roof in high winds, add less to the resale value of the home, relative to their cost."

"Future trends in hurricane frequency and intensity remain very uncertain. Experiments with climate models with sufficient resolution to depict some aspects individual hurricanes tend to project some increases in both peak wind speeds and precipitation intensities. The pattern is clearer for extra-tropical storms which are likely to become more intense, but perhaps less frequent, leading to increased extreme wave heights in the mid-latitudes."

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Climate Change 2007: Synthesis Report
Issued November 17th

Key Passages:

Observed Changes; Causes of Change

"Advances since the TAR [Third Assessment Report] show that discernible human influences extend beyond average temperature to other aspects of climate.

"Human influences have:

Projected Change and Its Impacts

"Some systems, sectors and regions are likely to be especially affected by climate change.

"Particular ecosystems:


"Altered frequencies and intensities of extreme weather, together with sea level rise, are expected to have mostly adverse effects on natural and human systems."

Greenland Ice Sheet and Sea Level Rise

"Contraction of the Greenland ice sheet is projected to continue to contribute to sea level rise after 2100. Current models suggest virtually complete elimination of the Greenland ice sheet and a resulting contribution to sea level rise of about 7 m if global average warming were sustained for millennia in excess of 1.9 to 4.6°C relative to pre-industrial values. The corresponding future temperatures in Greenland are comparable to those inferred for the last interglacial period 125,000 years ago, when paleoclimatic information suggests reductions of polar land ice extent and 4 to 6 m of sea level rise."

"Current global model studies project that the Antarctic ice sheet will remain too cold for widespread surface melting and gain mass due to increased snowfall. However, net loss of ice mass could occur if dynamical ice discharge dominates the ice sheet mass balance."

"Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change."

The Long-Term Perspective; Reasons for Concern

"There is high confidence that neither adaptation nor mitigation alone can avoid all climate change impacts; however, they can complement each other and together can significantly reduce the risks of climate change."

"Sea level rise under warming is inevitable. Thermal expansion would continue for many centuries after GHG concentrations have stabilised, for any of the stabilisation levels assessed, causing an eventual sea level rise much larger than projected for the 21st century."

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