Evidence, Agreement, Confidence and Likelihood
Where uncertainty is assessed qualitatively, it is characterised by … the amount and quality of EVIDENCE [eg "limited", "medium", "robust"] and the degree of AGREEMENT [eg "low", "medium", "high"] in the literature on a particular finding …
This approach is used by [Working Group III (Mitigation of Climate Change)] …
Where uncertainty is assessed more quantitatively using expert judgement of the correctness of underlying data, models or analyses, then the following scale of CONFIDENCE levels is used[:]
- very high confidence at least 9 out of 10;
- high confidence about 8 out of 10;
- medium confidence about 5 out of 10;
- low confidence about 2 out of 10; and
- very low confidence less than 1 out of 10.
Where uncertainty in specific outcomes is assessed using expert judgment and statistical analysis of a body of evidence (eg observations or model results), then the following LIKELIHOOD ranges are use …
| Virtually certain | >99% |
| Extremely Likely | >95% |
| Very Likely | >90% |
| Likely | >66% |
| More likely than not | >50% |
| About as likely as not | 33% to 66% |
| Unlikely | <33% |
| Very unlikely | <10% |
| Extremely unlikely | <5% |
| Exceptionally unlikely | <1% |
[Working Group II (Impacts, Adaptation and Vulnerability)] has used a combination of confidence and likelihood assessments …
[Working Group I (The Physical Science Basis)] has predominantly used likelihood assessments.
(Climate Change 2007: Synthesis Report, p 27)
Contents
Observed Changes
Causes of Changes
Impacts
Adaptation and Mitigation Options
The Long Term Perspective
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Climate Change 2007
- Climate Change 2007: Synthesis Report, adopted section by section at IPCC Plenary XXVII, Valencia, 12-17 November, 2007.
Core Writing Team:
Lenny Bernstein, Peter Bosch, Osvaldo Canziani, Zhenlin Chen, Renate Christ, Ogunlade Davidson, William Hare, Saleemul Huq, David Karoly, Vladimir Kattsov, Zbigniew Kundzewicz, Jian Liu, Ulrike Lohmann, Martin Manning, Taroh Matsuno, Bettina Menne, Bert Metz, Monirul Mirza, Neville Nicholls, Leonard Nurse, Rajendra Pachauri, Jean Palutikof, Martin Parry, Dahe Qin, Nijavalli Ravindranath, Andy Reisinger, Jiawen Ren, Keywan Riahi, Cynthia Rosenzweig, Matilde Rusticucci, Stephen Schneider, Youba Sokona, Susan Solomon, Peter Stott, Ronald Stouffer, Taishi Sugiyama, Rob Swart, Dennis Tirpak, Coleen Vogel and Gary Yohe.
Extended Writing Team:
Terry Barker.
Review Editors:
Abdelkader Allali, Roxana Bojariu, Sandra Diaz, Ismail Elgizouli, Dave Griggs, David Hawkins, Olav Hohmeyer, Bubu Pateh Jallow, Lucka Kajfez-Bogataj, Neil Leary, Hoesung Lee and David Wratt.
1 Observed changes in climate and their effects
1.1 Observations of climate change
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.
(p 30)
1.2 Observed effects of climate changes
Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.
(p 31)
Other effects of regional climate changes on natural and human environments are emerging, although many are difficult to discern due to adaptation and non-climatic drivers.
1.3 Consistency of changes in physical and biological systems with warming
Of the more than 29,000 observational data series, from 75 studies, that show significant change in many physical and biological systems, more than 89% are consistent with the direction of change expected as a response to warming …
(p 33)
2 Causes of change
2.1 Emissions of long-lived GHGs
Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004.
(p 36)
2.2 Drivers of climate change
Global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years.
The atmospheric concentrations of CO2 and CH4 in 2005 exceed by far the natural range over the last 650,000 years.
Global increases in CO2 concentrations are due primarily to fossil fuel use, with land-use change providing another significant but smaller contribution.
It is very likely that the observed increase in CH4 concentration is predominantly due to agriculture and fossil fuel use.
The increase in N2O concentration is primarily due to agriculture. …
There is very high confidence that the global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W/m^2.
(p 37)
2.4 Attribution of climate change
Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.
This is an advance since the TAR’s [Third Assessment Report] conclusion thatmost of the observed warming over the last 50 years is
likely to have been due to the increase in GHG concentrations.
It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica).
(p 39)
Advances since the TAR show that discernible human influences extend beyond average temperature to other aspects of climate, including temperature extremes and wind patterns.
(p 40)
Anthropogenic warming over the last three decades has likely had a discernible influence at the global scale on observed changes in many physical and biological systems.
(p 41)
3 Climate change and its impacts in the near and long term under different scenarios
3.1 Emissions scenarios
There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades.
Baseline emissions scenarios published since the IPCC Special Report on Emissions Scenarios (SRES, 2000) are comparable in range to those presented in SRES.
(p 45)SRES scenarios
SRES refers to the scenarios described in the IPCC Special Report on Emissions Scenarios.
The SRES scenarios are grouped into four scenario families … that explore alternative development pathways …
[A1] assumes a world of very rapid economic growth, a global population that peaks in mid-century and rapid introduction of new and more efficient technologies.
A1 is divided into three groups …- fossil intensive (A1FI),
- non-fossil energy resources (A1T) and
- a balance across all sources (A1B).
{A2 describes a very heterogeneous world with high population growth, slow economic development and slow technological change.}
B1 describes a [world] with the same global population as A1, but with more rapid changes in economic structures toward a service and information economy.
B2 describes a world with intermediate population and economic growth, emphasising local solutions to economic, social, and environmental sustainability.
3.2 Projections of future changes in climate
For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios.
Even if the concentrations of all GHGs and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
Afterwards, temperature projections increasingly depend on specific emissions scenarios.
3.2.1 21st century global changes
Continued GHG emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
(p 45)
3.2.2 21st century regional changes
There is now higher confidence than in the TAR in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation and some aspects of extremes and sea ice.
3.2.3 Changes beyond the 21st century
Anthropogenic warming and sea level rise would continue for centuries due to the time scales associated with climate processes and feedbacks, even if GHG concentrations were to be stabilised.
(p 46)
3.3 Impacts of future climate changes
More specific information is now available across a wide range of systems and sectors concerning the nature of future impacts, including some fields not covered in previous assessments.
(p 48)
Studies since the TAR have enabled more systematic understanding of the timing and magnitude of impacts related to differing amounts and rates of climate change.
3.3.2 Impacts on regions
Australia and New Zealand- By 2020, significant loss of biodiversity is projected to occur in some ecologically rich sites, including the Great Barrier Reef and Queensland Wet Tropics.
- By 2030, water security problems are projected to intensify in southern and eastern Australia and, in New Zealand, in Northland and some eastern regions.
- By 2030, production from agriculture and forestry is projected to decline over much of southern and eastern Australia, and over parts of eastern New Zealand, due to increased drought and fire.
However, in New Zealand, initial benefits are projected in some other regions. - By 2050, ongoing coastal development and population growth in some areas of Australia and New Zealand are projected to exacerbate risks from sea level rise and increases in the severity and frequency of storms and coastal flooding.
3.3.3 Especially affected systems, sectors and regions
Some systems, sectors and regions are likely to be especially affected by climate change.
3.3.5 Extreme events
Altered frequencies and intensities of extreme weather, together with sea level rise, are expected to have mostly adverse effects on natural and human systems.
(p 52)
3.4 Risk of abrupt or irreversible changes
Anthropogenic warming could lead to some impacts that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.
(p 53)
4 Adaptation and mitigation options and responses, and the inter-relationship with sustainable development, at global and regional levels
4.2 Adaptation options
Adaptation can reduce vulnerability, both in the short and the long term. …
Adaptive capacity is intimately connected to social and economic development, but it is not evenly distributed across and within societies.
(p 56)
4.3 Mitigation options
Both bottom-up and top-down studies indicate that there is high agreement and much evidence of substantial economic potential for the mitigation of global GHG emissions over the coming decades that could offset the projected growth of global emissions or reduce emissions below current levels.
(p 58)
While studies use different methodologies, there is high agreement and medium evidence that in all analysed world regions near-term health co-benefits from reduced air pollution, as a result of actions to reduce GHG emissions, can be substantial and may offset a substantial fraction of mitigation costs. …
Literature since the TAR confirms with high agreement and medium evidence that there may be effects from Annex I countries’ action on the global economy and global emissions, although the scale of carbon leakage remains uncertain. …
There is also high agreement and medium evidence that changes in lifestyle and behaviour patterns can contribute to climate change mitigation across all sectors.
Management practices can also have a positive role. …
Policies that provide a real or implicit price of carbon could create incentives for producers and consumers to significantly invest in low-GHG products, technologies and processes.
(p 59)
There is high agreement and much evidence that a wide variety of national policies and instruments are available to governments to create the incentives for mitigation action.
Their applicability depends on national circumstances and an understanding of their interactions, but experience from implementation in various countries and sectors shows there are advantages and disadvantages for any given instrument.
4.4 Relationship between adaptation and mitigation options and relationship with sustainable development
There is growing understanding of the possibilities to choose and implement climate response options in several sectors to realise synergies and avoid conflicts with other dimensions of sustainable development. …
Both synergies and trade-offs exist between adaptation and mitigation options.
(p 61)
4.5 International and regional cooperation
There is high agreement and much evidence that notable achievements of the UNFCCC and its Kyoto Protocol are the establishment of a global response to the climate change problem, stimulation of an array of national policies, the creation of an international carbon market and the establishment of new institutional mechanisms that may provide the foundation for future mitigation efforts.
Progress has also been made in addressing adaptation within the UNFCCC and additional initiatives have been suggested.
(p 62)
5 The long-term perspective: scientific and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the convention, and in the context of sustainable development
5.2 Key vulnerabilities, impacts and risks — long-term perspectives
The five ‘reasons for concern’ identified in the TAR are now assessed to be stronger with many risks identified with higher confidence.
Some are projected to be larger or to occur at lower increases in temperature.
This is due to- better understanding of the magnitude of impacts and risks associated with increases in global average temperature and GHG concentrations, including vulnerability to present-day climate variability,
- more precise identification of the circumstances that make systems, sectors, groups and regions especially vulnerable and
- growing evidence that the risk of very large impacts on multiple century time scales would continue to increase as long as GHG concentrations and temperature continue to increase.
(p 64)
5.3 Adaptation and mitigation
There is high confidence that neither adaptation nor mitigation alone can avoid all climate change impacts.
Adaptation is necessary both in the short term and longer term to address impacts resulting from the warming that would occur even for the lowest stabilisation scenarios assessed.
There are barriers, limits and costs that are not fully understood.
Adaptation and mitigation can complement each other and together can significantly reduce the risks of climate change.
(p 65)
Efforts to mitigate GHG emissions to reduce the rate and magnitude of climate change need to account for inertia in the climate and socio-economic systems.
5.4 Emission trajectories for stabilisation
In order to stabilise the concentration of GHGs in the atmosphere, emissions would need to peak and decline thereafter.
The lower the stabilisation level, the more quickly this peak and decline would need to occur. …
Mitigation efforts over the next two to three decades will have a large impact on opportunities to achieve lower stabilisation levels.
(p 66)
5.5 Technology flows and development
There is high agreement and much evidence that all stabilisation levels assessed can be achieved by deployment of a portfolio of technologies that are either currently available or expected to be commercialised in coming decades, assuming appropriate and effective incentives are in place for development, acquisition, deployment and diffusion of technologies and addressing related barriers.
(p.68)
5.6 Costs of mitigation and long-term stabilisation targets
The macro-economic costs of mitigation generally rise with the stringency of the stabilisation target and are relatively higher when derived from baseline scenarios characterised by high emission levels.
5.7 Costs, benefits and avoided climate impacts at global and regional levels
Impacts of climate change will vary regionally.
Aggregated and discounted to the present, they are very likely to impose net annual costs, which will increase over time as global temperatures increase. …
Limited and early analytical results from integrated analyses of the global costs and benefits of mitigation indicate that these are broadly comparable in magnitude, but do not as yet permit an unambiguous determination of an emissions pathway or stabilisation level where benefits exceed costs. …
Many impacts can be avoided, reduced or delayed by mitigation.
(p 69)
5.8 Broader environmental and sustainability issues
Sustainable development can reduce vulnerability to climate change, and climate change could impede nations’ abilities to achieve sustainable development pathways.
Making development more sustainable can enhance mitigative and adaptive capacities, reduce emissions, and reduce vulnerability, but there may be barriers to implementation.
(p 70)
