使用者:Towerman/translation/政府間氣候變化專門委員會第四次評估報告

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政府間氣候變化專門委員會第四次評估報告是政府間氣候變化專門委員會（IPCC）針對氣候變化及其影響的第四個綜合評估報告。該報告的全名是《氣候變化2007：聯合國政府間氣候變化專門委員會第四次評估報告》（Climate Change 2007, the Fourth Assessment Report (AR4) of the United Nations Intergovernmental Panel on Climate Change），因此常被簡稱「IPCC第四次評估報告」，或「氣候變化2007」報告，或「AR4」報告。IPCC的任務是對全球範圍內有關氣候變化及其影響、氣候變化減緩和適應措施的科學、技術、社會、經濟方面的信息進行評估，並根據需求為《聯合國氣候變化框架公約》（UNFCCC）實施提供科學技術諮詢。作為IPCC的主要工作，此前於1990年、1995年和2001年，IPCC已經相繼完成了三次評估報告，下一份報告計劃於2014年出版。IPCC不直接評估政策問題，但所評估的科學問題均與政策相關。此次發布的評估報告，在吸納了此前開展的各項評估以及過去6年最新科研成果的基礎上，闡述了當前對氣候變化主要原因、氣候變化觀測事實、氣候的多種過程和歸因以及一系列未來氣候變化預估結果的科學認識水平。該報告是迄今以來有關氣候變化的最長和最詳細的總結，來自幾十個國家的上千名專家參與了該報告的寫作，編輯和評審等工作，報告共引用了6000多篇同行評議的科學文獻。報告已成為國際社會認識和了解氣候變化問題的主要科學依據，對氣候變化國際談判產生了重要影響。該報告的首要發現或結論是：「氣候系統正在變暖是毫不含糊的（unequivocal）」，以及「自20世紀中期以來所觀測到的全球平均氣溫的上升非常可能（very likely）是由於觀測到的人為溫室氣體排放的增加造成的」。儘管該報告是全世界大多數科學家對氣候變化的共識，但還是有一些批評意見出現。

概況

IPCC第四次評估報告共有四個部分，於2007年不同時間分別發行。前三個部分是IPCC的三個工作小組對不同議題的分別報告，第四個報告是一個總結報告。這四個報告為：

• 第一工作組報告（WGI）：《氣候變化2007: 科學基礎》
• 第二工作組報告（WGII）：《氣候變化2007: 影響、適應性和脆弱性》
• 第三工作組報告（WGIII）：《氣候變化2007: 減緩氣候變化》
• 綜合報告（SYR）：《氣候變化2007: 綜合報告》

每個報告又由兩大部分組成：決策者摘要和主報告。

第一工作組報告（WGI）：科學基礎

使用第四次評估報告中的四個SRES排放方案得到的相應的全球平均地面溫度在2100年的預測值
AR4 (決策者摘要; PDF)	更多的經濟考慮	更多的環境考慮
全球化 （同一化的世界）	A1 快速的經濟發展 （分組：A1T；A1B；A1Fl） 1.4～6.4 °C	B1 全球環境可持續性  1.1～2.9 °C
區域化 （多樣化的世界）	A2 區域定向的經濟發展 2.0～5.4 °C	B2 本地的環境可持續性 1.4～3.8 °C

第一工作組的決策者摘要（SPM）於2007年2月2日出版，2007年2月5日再版。完整的第一工作組報告於3月出版，9月5日最後一次更新。一份34頁長的「常見問題」文檔也已經被提供。

第一工作組的報告（《氣候變化2007：科學基礎》）「評估了有關氣候變化的人為和自然驅動力、觀測到的氣候變化、將這些變化歸因到不同原因的能力、預測未來的氣候變化等方面的當前科學認識」。

有來自40個國家的大約600名作者合作寫出了這個報告。超過620個專家或政府審閱了該報告。報告引用了超過6000份科學文獻。

正式通過該報告之前，在法國巴黎於1月29日到2月1日召開了第一工作組的第10次工作會議。在這次會議上，來自113個國家的代表逐行審議了該報告的決策者摘要。

對於全球暖化及其原因，該摘要（SPM）認為：

• 「氣候系統的變暖是毫無疑問的。」
• 「自20世紀中期以來，絕大部分被觀測到的全球平均地面溫度的升高非常可能是因為觀測到的人為排放的溫室氣體的濃度增加而引起的。」

該摘要在第3頁的腳註6解釋，非常可能和可能分別意味著「通過專家們的判斷，被評估的可能性」是90%和66%以上。

觀測

這份報告提到了許多觀測到的地球氣候系統的變化，包括有大氣成分，全球平均溫度，海洋狀況，以及其他氣候變化。

大氣的變化

二氧化碳，甲烷和氧化亞氮都是長壽命的溫室氣體。

• 「由於1750年以來的人類活動，二氧化碳、甲烷以及氧化亞氮已經顯著的增加，並遠遠超過工業化前的水平。」
• 2005年二氧化碳在大氣中的含量已經超過了(379 ppm)，這個值已經高於最近650,000年來的自然變動範圍（180－300ppm）。
• 2005年大氣中的甲烷含量（1774ppb）已經遠遠超過最近65萬年的自然變化範圍（320～790ppb）。
• 二氧化碳增加的首要來源是化石燃料，但土地利用的變化也是很大的原因。
• 甲烷增加的首要來源非常可能是人類農業活動和使用化石燃料。但每個因素具體貢獻多少甲烷增加還沒有很確定的數字。
• 氧化亞氮的濃度已經由工業化以前的270ppb上升到319ppb（2005年）。至少三分之一的甲烷增加是因為人類活動，其中農業活動又占到首位。

地球變暖

冷天已經變得少些了，熱天和熱浪出現的跟頻繁了。另外：

• 在最近的12年裡（1995至2006年），有11年的都排在儀器測量到的溫度記錄（自1880年）里的最熱的12個年份里。
• 最近100年來的變暖以經使得全球平均氣溫上升了大約0.74°C。第三次氣候評估報告（AR3）估計的100年裡增加的溫度還只是0.6°C。
• 熱島效應已經被證明對全球平均氣溫的影響十分微小（平均每10年造成陸地升溫少於0.0006°C，對海洋的影響為0）。
• 自1961年以來的觀測記錄顯示，加入氣候系統的熱量中超過80%的部分被海洋吸收。海洋溫度的上升已經使得海洋深度達到至少3000米（9800英尺）。
• 「北極的平均氣溫在過去100年裡的上升速度是全球氣溫上升速度的大致2倍。」
• 如果沒有火山噴發及人為產生的氣膠的冷卻效應，排放的溫室氣體可能會造成更大的升溫。（參見全球黯化）
• 20世紀後50年的北半球平均氣溫很有可能比過去500年來其他任意一個50年的氣溫都高，甚至有可能是至少過去1300年（接近小冰期的開始）來最高的。

Ice, snow, permafrost, rain, and the oceans

The SPM documents increases in wind intensity, decline of permafrost coverage, and increases of both drought and heavy precipitation events. Additionally:

• "Mountain glaciers and snow cover have declined on average in both hemispheres."
• Losses from the land-based ice sheets of Greenland and Antarctica have very likely (>90%) contributed to sea level rise between 1993 and 2003.
• Ocean warming causes seawater to expand, which contributes to sea level rising.
• Sea level rose at an average rate of about 1.8 mm/year during the years 1961-2003. The rise in sea level during 1993-2003 was at an average rate of 3.1 mm/year. It is not clear whether this is a long-term trend or just variability.
• Antarctic sea ice shows no significant overall trend, consistent with a lack of warming in that region.

颶風

• There has been an increase in hurricane intensity in the North Atlantic since the 1970s, and that increase correlates with increases in sea surface temperature.
• The observed increase in hurricane intensity is larger than climate models predict for the sea surface temperature changes we have experienced.
• There is no clear trend in the number of hurricanes.
• Other regions appear to have experienced increased hurricane intensity as well, but there are concerns about the quality of data in these other regions.
• It is more likely than not (>50%) that there has been some human contribution to the increases in hurricane intensity.
• It is likely (>66%) that we will see increases in hurricane intensity during the 21st century.

Table SPM-2 lists recent trends along with certainty levels for the trend having actually occurred, for a human contribution to the trend, and for the trend occurring in the future. In relation to changes (including increased hurricane intensity) where the certainty of a human contribution is stated as "more likely than not" footnote f to table SPM-2 notes "Magnitude of anthropogenic contributions not assessed. Attribution for these phenomena based on expert judgment rather than formal attribution studies."

使地球變暖或變冷的因素

Changes in radiative forcings between 1750 and 2005 as estimated by the IPCC.

AR4 describes warming and cooling effects on the planet in terms of radiative forcing — the rate of change of energy in the system, measured as power per unit area (in SI units, W/m²). The report shows in detail the individual warming contributions (positive forcing) of carbon dioxide, methane, nitrous oxide, halocarbons, other human warming factors, and the warming effects of changes in solar activity. Also shown are the cooling effects (negative forcing) of aerosols, land-use changes, and other human activities. All values are shown as a change from pre-industrial conditions.

• Total radiative forcing from the sum of all human activities is a warming force of about +1.6 watts/m²
• Radiative forcing from an increase of solar intensity since 1750 is about +0.12 watts/m²
• Radiative forcing from carbon dioxide, methane, and nitrous oxide combined is very likely (>90%) increasing more quickly during the current era (1750-present) than at any other time in the last 10,000 years.

Climate sensitivity

Climate sensitivity is defined as the amount of global average surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range of 2 to 4.5 °C, with a best estimate of about 3 °C. This range of values is not a projection of the temperature rise we will see in the 21st century, since the future change in carbon dioxide concentrations is unknown, and factors besides carbon dioxide concentrations affect temperature.

Model-based projections for the future

Model projections are made based on an analysis of various computer climate models running within different SRES scenarios. As a result, predictions for the 21st century are as shown below.

• Surface air warming in the 21st century:
  • Best estimate for a "low scenario" is 1.8 °C with a likely range of 1.1 to 2.9 °C (3.2 °F with a likely range of 2.0 to 5.2 °F)
  • Best estimate for a "high scenario" is 4.0 °C with a likely range of 2.4 to 6.4 °C (7.2 °F with a likely range of 4.3 to 11.5 °F)
  • A temperature rise of about 0.1 °C per decade would be expected for the next two decades, even if greenhouse gas and aerosol concentrations were kept at year 2000 levels.
  • A temperature rise of about 0.2 °C per decade is projected for the next two decades for all SRES scenarios.
  • Confidence in these near-term projections is strengthened because of the agreement between past model projections and actual observed temperature increases.
• Based on multiple models that all exclude ice sheet flow due to a lack of basis in published literature, it is estimated that sea level rise will be:
  • in a low scenario 18 to 38 cm (7 to 15 inches)
  • in a high scenario 26 to 59 cm (10 to 23 inches)
• It is very likely that there will be an increase in frequency of warm spells, heat waves and events of heavy rainfall.
• It is likely that there will be an increase in areas affected by droughts, intensity of tropical cyclones (which include hurricanes and typhoons) and the occurrence of extreme high tides.
• "Sea ice is projected to shrink in both the Arctic and Antarctic … In some projections, Arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century."

Scenario-specific projections are based on analysis of multiple runs by multiple climate models, using the various SRES Scenarios. "Low scenario" refers to B1, the most optimistic scenario family. "High scenario" refers to A1FI, the most pessimistic scenario family.

Temperature and sea level rise for each SRES scenario family

There are six families of SRES Scenarios, and AR4 provides projected temperature and sea level rises for each scenario family.

• Scenario B1
  • Best estimate temperature rise of 1.8 °C with a likely range of 1.1 to 2.9 °C (3.2 °F with a likely range of 2.0 to 5.2 °F)
  • Sea level rise likely range [18 to 38 cm] (7 to 15 inches)
• Scenario A1T
  • Best estimate temperature rise of 2.4 °C with a likely range of 1.4 to 3.8 °C (4.3 °F with a likely range of 2.5 to 6.8 °F)
  • Sea level rise likely range [20 to 45 cm] (8 to 18 inches)
• Scenario B2
  • Best estimate temperature rise of 2.4 °C with a likely range of 1.4 to 3.8 °C (4.3 °F with a likely range of 2.5 to 6.8 °F)
  • Sea level rise likely range [20 to 43 cm] (8 to 17 inches)
• Scenario A1B
  • Best estimate temperature rise of 2.8 °C with a likely range of 1.7 to 4.4 °C (5.0 °F with a likely range of 3.1 to 7.9 °F)
  • Sea level rise likely range [21 to 48 cm] (8 to 19 inches)
• Scenario A2
  • Best estimate temperature rise of 3.4 °C with a likely range of 2.0 to 5.4 °C (6.1 °F with a likely range of 3.6 to 9.7 °F)
  • Sea level rise likely range [23 to 51 cm] (9 to 20 inches)
• Scenario A1FI
  • Best estimate temperature rise of 4.0 °C with a likely range of 2.4 to 6.4 °C (7.2 °F with a likely range of 4.3 to 11.5 °F)
  • Sea level rise likely range [26 to 59 cm] (10 to 23 inches)

Selected quotes from the WGI Summary for Policymakers

• "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."

對WGI報告的反應

在第一工作組的報告出版前幾周，對於報告所預計的未來海平面的變化就有了爭議。正式報告中有關海平面變化的估計值小於之前的幾次估計值。正式報告中警告說這個海平面變化的估計值可能太低：「有關冰流的一些動態過程沒有被包括在當前的模式里，但是一些最近的觀測表明這些過程可能會使得面對全球暖化時冰面的脆弱性加大，從而加大未來海平面得上升。」這些海平面上升的估計值的中點是在IPCC第三次評估報告（TAR）的估計值的±10%以內，但是這個範圍已經縮小了。

英國皇家學會主席里斯勳爵說，「這個報告比以往更令人信服的清楚地指出，人類活動對我們正看到的和將看到的氣候改變有很大責任。IPCC強烈的強調，真實的氣候改變是不可避免的，我們將不得不去適應這個改變。這必將迫使包括世界領導人、商界人士和個人在內的我們所有人開始行動，而不是恐懼得癱瘓。我們不僅僅需要減少我們排放的溫室氣體，還應為氣候變化的影響做好準備。那些聲稱有不同意見的人將無法以科學為接口來支持他們的論調了。」

美國能源部部長塞繆爾·博德曼（Samuel Bodman）在一次新聞發布會上說，這份報告「科學合理」，並且，「像總統一直在說的一樣，該報告清楚的闡明了，人類活動對我們地球的氣候改變有貢獻，這個問題已經不需要再爭論了。」美國負責歐洲和歐亞事務的副助理國務卿科特·沃爾克（Kurt Volker）說，「我們支持這份由美國科學家領導寫出的最近的IPCC報告。」

基於這份報告，在由法國總統席哈克宣讀的「巴黎行動宣言」（Paris Call for Action）中，46個國家號召創立一個聯合國環境組織（United Nations Environment Organization；UNEO），並賦予其比現有的聯合國環境署（UNEP）更多的權力，將類似於有較多權力的世界衛生組織。 這46個國家包括了歐盟，但沒有包括美國、中國、俄羅斯和印度這四個最主要的溫室氣體排放國。

第二工作組報告（WGII）：影響、適應和脆弱性

第二工作組報告（WGII）的決策者摘要於2007年4月6日發布。全報告於2007年9月18日發布。

WGII認為「來自於所有大陸和大部分海洋的證據表明許多自然系統正在被區域氣候的變化所影響，特別是升高的溫度的影響。」

Observations

Some observed changes have been associated with climate change at varying levels of confidence.

With a High Confidence (about an 8 in 10 chance to be correct) WGII asserts that climate change has resulted in:

• More and larger glacial lakes.
• Increasing ground instability in permafrost regions.
• Increasing rock avalanches in mountain regions.
• Changes in some Arctic and Antarctic ecosystems.
• Increased run-off and earlier spring peak discharge in many glacier and snow-fed rivers.
• Changes affecting algae, plankton, fish and zooplankton because rising water temperatures and changes in:
  • ice cover
  • salinity
  • oxygen levels
  • water circulation

With a Very High Confidence (about a 9 in 10 chance to be correct) WGII asserts that climate change is affecting terrestrial biological systems in that:

• Spring events such as the unfolding of leaves, laying of eggs, and migration are happening earlier.
• There are poleward and upward (to higher altitude) shifts in ranges of plant and animal species.

WGII also states that the ocean has become more acidic because it has absorbed human-caused carbon dioxide. Ocean pH has dropped by 0.1, but how this affects marine life is not documented.

Attribution of Changes

WGII acknowledges some of the difficulties of attributing specific changes to human-caused global warming, stating that "Limitations and gaps prevent more complete attribution of the causes of observed system responses to anthropogenic warming." but found that the agreement between observed and projected changes was "Nevertheless ... sufficient to conclude with high confidence that anthropogenic warming over the last three decades has had a discernible influence on many physical and biological systems."

Projections

WGII describes some of what might be expected in the coming century, based on studies and model projections.

Fresh Water

It is projected with High Confidence that:

• Dry regions are projected to get drier, and wet regions are projected to get wetter: "By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics..."
• Drought-affected areas will become larger.
• Heavy precipitation events are very likely to become more common and will increase flood risk.
• Water supplies stored in glaciers and snow cover will be reduced over the course of the century.

Ecosystems

It is projected with High Confidence that:

• The resilience of many ecosystems is likely to be exceeded this century by a combination of climate change and other stressors.
• Carbon removal by terrestrial ecosystems is likely to peak before mid-century and then weaken or reverse. This would amplify climate change.

Food

It is projected with Medium Confidence (about 5 in 10 chance to be correct) that globally, potential food production will increase for temperature rises of 1-3 °C, but decrease for higher temperature ranges. Fortunately, temperatures are not expected to rise to these ranges in the near future.

Coastal Systems

It is projected with Very High Confidence that:

• Coasts will be exposed to increasing risks such as coastal erosion due to climate change and sea-level rise.
• "Increases in sea-surface temperature of about 1-3 °C are projected to result in more frequent coral bleaching events and widespread mortality unless there is thermal adaptation or acclimatisation by corals."
• "Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s."

Objections to original WGII language

U.S. negotiators managed to eliminate language calling for cuts in greenhouse gas emissions, according to Patricia Romero Lankao, a lead author from the National Center for Atmospheric Research (NCAR). The original draft read: "However, adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude. Mitigation measures will therefore also be required." The second sentence does not appear in the final version of the report.

China objected to wording that said "based on observed evidence, there is very high confidence that many natural systems, on all continents and in most oceans, are being affected by regional climate changes, particularly temperature increases." When China asked that the word "very" be stricken, three scientific authors balked, and the deadlock was broken only by a compromise to delete any reference to confidence levels.

第三工作組報告（WGIII）：減緩氣候變化

參見：減緩全球暖化

第三工作組的決策者摘要（SPM）於2007年5月4日在該組的第26次工作會議上發布。 The full WG III report was published online in September, 2007.

IPCC召集會議於4月30日在曼谷開始討論該組報告的決策者摘要的草稿。有來自大約120個國家的超過400位科學家和專家參加了此次會議。在5月4日的IPCC全體會議上，這2000多位代表的大多數同意了該摘要。會議上主要的一個爭議是有關一個限制溫室氣體濃度的提案。為了避免危險的氣候變化，該提案建議到2030年將溫室氣體濃度限制於445～650ppm之間，但開發中國家施壓提高低限濃度。儘管如此，來自於原始提案的圖表還是被寫入決策者摘要中。該摘要下結論說，溫室氣體濃度的穩定將需要一個適度的代價，比如濃度穩定於445ppm～535ppm將花費少於3%的全球GDP。

第三工作組報告分析了對於主要部門在近期可選的減緩氣候變化的方式，同時也提到了一些有關跨部門的事情，比如合作，互利，和交易。報告也根據不同的穩定濃度目標給出了相應的減緩氣候變化的長期戰略，同時也強調了應用不同的短期戰略來達到長期目標。

短期和中期減緩（至2030年）

The Summary for Policymakers concludes that there was a high level of agreement and much evidence that 'there is substantial economic potential for the mitigation of global greenhouse gas emissions over the coming decades, that could offset the projected growth of global emissions or reduce emissions below current levels', taking into account financial and social costs and benefits. The technologies with the largest economic potential within this timescale are considered to be:

Key mitigation technologies and practices by sector

Sector	Key mitigation technologies and practices currently commercially available	Key mitigation technologies and practices projected to be commercialized before 2030
Energy Supply	Improved supply and distribution efficiency; fuel switching from coal to gas; nuclear power; renewable heat and power (hydropower, solar, wind, geothermal and bioenergy); combined heat and power; early applications of CCS (e.g. storage of removed CO2 from natural gas)	Carbon Capture and Storage (CCS) for gas, biomass and coal-fired electricity generating facilities; advanced nuclear power; advanced renewable energy, including tidal and waves energy, concentrating solar, and solar PV.
Transport	More fuel efficient vehicles; hybrid vehicles; cleaner diesel vehicles; biofuels; modal shifts from road transport to rail and public transport systems; non-motorised transport (cycling, walking); land-use and transport planning	Second generation biofuels; higher efficiency aircraft; advanced electric and hybrid vehicles with more powerful and reliable batteries
Buildings	Efficient lighting and daylighting; more efficient electrical appliances and heating and cooling devices; improved cook stoves, improved insulation; passive and active solar design for heating and cooling; alternative refrigeration fluids, recovery and recycle of fluorinated gases	Integrated design of commercial buildings including technologies, such as intelligent meters that provide feedback and control; solar PV integrated in buildings
Industry	More efficient end-use electrical equipment; heat and power recovery; material recycling and substitution; control of non-CO2 gas emissions; and a wide array of process-specific technologies	Advanced energy efficiency; CCS for cement, ammonia, and iron manufacture; inert electrodes for aluminium manufacture
Agriculture	Improved crop and grazing land management to increase soil carbon storage; restoration of cultivated peaty soils and degraded lands; improved rice cultivation techniques and livestock and manure management to reduce CH4 emissions; improved nitrogen fertilizer application techniques to reduce N2O emissions; dedicated energy crops to replace fossil fuel use; improved energy efficiency	Improvements of crop yields
Forestry/forests	Afforestation; reforestation; forest management; reduced deforestation; harvested wood product management; use of forestry products for bio-energy to replace fossil fuel use	Tree species improvement to increase biomass productivity and carbon sequestration. Improved remote sensing technologies for analysis of vegetation/ soil carbon sequestration potential and mapping land use change
Waste	Landfill methane recovery; waste incineration with energy recovery; composting of organic waste; controlled waste water treatment; recycling and waste minimization	Biocovers and biofilters to optimize CH4 oxidation

The IPCC estimates that stabilizing atmospheric greenhouse gases at between 445-535ppm CO₂ equivalent would result in a reduction of average annual GDP growth rates of less than 0.12%. stabilizing at 535 to 590ppm would reduce average annual GDP growth rates by 0.1%, while stabilization at 590 to 710ppm would reduce rates by 0.06%. There was high agreement and much evidence that a substantial fraction of these mitigation costs may be offset by benefits to health as a result of reduced air pollution, and that there would be further cost savings from other benefits such as increased energy security, increased agricultural production, and reduced pressure on natural ecosystems as well as, in certain countries, balance of trade improvements, provision of modern energy services to rural areas and employment.

The IPCC considered that achieving these reductions would require a 'large shift in the pattern of investment, although the net additional investment required ranges from negligible to 5-10%'.They also concluded that it is often more cost effective to invest in end-use energy efficiency improvement than in increasing energy supply.

In terms of electricity generation, the IPCC envisage that renewable energy can provide 30 to 35% of electricity by 2030 (up from 18% in 2005) at a carbon price of up to US$50/t, and that nuclear power can rise from 16% to 18%. They also warn that higher oil prices might lead to the exploitation of high-carbon alternatives such as oil sands, oil shales, heavy oils, and synthetic fuels from coal and gas, leading to increasing emissions, unless carbon capture and storage technologies are employed.

In the transport sector there was a medium level of agreement and evidence that the multiple mitigation options may be counteracted by increased use, and that there were many barriers and a lack of government policy frameworks.

There was high agreement and much evidence that, despite many barriers (particularly in the developing countries), new and existing buildings could reduce emissions considerably, and that this would also provide other benefits in terms of improved air quality, social welfare and energy security.

長期減緩（2030年後）

The IPCC reported that the effectiveness of mitigation efforts over the next two or three decades would have a large impact on the ability to stabilize atmospheric greenhouse gases at lower levels, and that the lower the ultimate stabilization levels, the more quickly emissions would need to peak and decline. For example, to stabilize at between 445 and 490ppm (resulting in an estimate global temperature 2 to 2.4^oC above the pre-industrial average) emissions would need to peak before 2015, with 50 to 85% reductions on 2000 levels by 2050.

There was high agreement and much evidence that stabilization could be achieved by 2050 using currently available technologies, provided appropriate and effective incentives were put in place for their development, acquisition, deployment and diffusion, and that barriers were removed. For stabilization at lower levels the IPCC agreed that improvements of carbon intensity need to be made much faster than has been the case in the past, and that there would be a greater need for efficient public and private research, development & demonstration efforts and investment in new technologies during the next few decades. The IPCC points out that government funding in real absolute terms for most energy research programmes has been flat or declining for nearly 20 years, and is now about half the 1980 level. Delays in cutting emissions would lead to higher stabilization levels and increase the risk of more severe climate change impacts, as more of the current high-emission technologies would have been deployed.

Among the measures that might be used, there was high agreement and much evidence that policies that put a price on the cost of carbon emissions could provide incentives for consumers and producers. Carbon prices of 5 to 65 US$/tCO₂ in 2030 and 15 to 130 US$/tCO₂ by 2050 are envisaged for stabilization at around 550 ppm by 2100.

綜合報告

A draft version of the AR4 Synthesis Report, Summary for Policymakers (SPM)PDF (1.92 MB), "Subject to final copyedit", was published 16 November, 2007.

The Synthesis Report goes one step further [than the first three Climate Change 2007 Working Group Reports]: it is the decisive effort to integrate and compact this wealth of information into a readable and concise document explicitly targeted to the policymakers.

The Synthesis Report also brings in relevant parts some material [sic] contained in the full Working Group Reports over and above what is included in the Summary for Policymakers in these three Reports. It is designed to be a powerful, scientifically authoritative document of high policy relevance, which will be a major contribution to the discussions at the 13th Conference of the Parties in Bali during December 2007. In fact, this Conference was postponed to December to allow the IPCC Synthesis Report to come out first.
— Undated IPCC press release

The six topics addressed in the Synthesis Report are:

1. Observed changes in climate and its effects (Working Groups 1-2).
2. Causes of change (WGs 1, 3).
3. Climate change and its impacts in the near and long term under different scenarios (WGs 1-3).
4. Adaptation and mitigation options and responses, and the inter-relationship with sustainable development, at global and regional levels (WGs 2-3).
5. The long term perspective: scientific and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the Convention [sic], and in the context of sustainable development (WGs 1-3).
6. Robust findings, key uncertainties (WGs 1-3).

The "Convention" mentioned in Topic 5 is the UN Framework Convention on Climate Change (UNFCCC).

The key findings from the AR4 Synthesis Report will be discussed Wednesday 13 December 2007 at the United Nations Climate Change Conference (UNFCCC COP 13--CMP 3) in Bali, Indonesia, which takes place 3-14 December (see UNFCCC home page).

人為的變暖可能導致一些突變或不可逆轉的影響

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

• "There is medium confidence that approximately 20-30% of species assessed so far are likely to be at increased risk of extinction if increases in global average warming exceed 1.5-2.5°C (relative to 1980-1999). As global average temperature increase exceeds about 3.5°C,

model projections suggest significant extinctions (40-70% of species assessed) around the globe."

• "Partial loss of ice sheets on polar land could imply metres of sea level rise, major changes in coastlines and inundation of low-lying areas, with greatest effects in river deltas and low-lying islands. Such changes are projected to occur over millennial time scales, but more rapid sea level rise on century time scales cannot be excluded."

批評

主條目：對IPCC第四次評估報告的批評

第四次評估報告已經受到批評。對人為引起全球暖化持懷疑者聲稱他們的意見沒有被充分的包括在這份報告中。也有些人認為IPCC對氣候變化帶來的潛在危害估計的過於保守。

因為和全球暖化這個大主題有關，第四次評估報告已經被許多方面評論過，比如政府官員、特殊利益團體、科學組織。有關圍繞全球暖化的政治以及各團體對之的態度的全面討論，可參看文章「全球暖化的政治」。

See also

• Avoiding Dangerous Climate Change – international conference (2005)
• Individual and political action on climate change
• Business action on climate change
• Energy policy
• Energy conservation
• Global climate model
• Post-Kyoto Protocol negotiations on greenhouse gas emissions
• Precautionary principle
• Renewable Energy Sources and Climate Change Mitigation
• World energy resources and consumption

外部連結

• IPCC (政府間氣候變化專門委員會)：
  • （英文）（簡體中文）官方主頁
  • IPCC第四次評估報告 (AR4):
    • 第一工作組報告（WGI）：科學基礎：
      • （英文）第一工作組主頁
      • （簡體中文）決策者摘要(SPM)PDF (3.3 MB)
      • （英文）全報告
      • （簡體中文）常見問題PDF (7.16 MB) — 這34頁的常見問題（FAQ）都是根據共有11章的全報告編寫的
    • 第二工作組報告（WGI）：影響、適應性和脆弱性：
      • （英文）第二工作組主頁
      • （簡體中文）決策者摘要(SPM)PDF (1.1 MB)
      • （英文）全報告
    • 第三工作組報告（WGIII）：減緩氣候變化：
      • （英文）第三工作組主頁
      • （簡體中文）決策者摘要(SPM)PDF (1.5 MB)
      • （英文）全報告
    • 綜合報告（SYR）：
      • （簡體中文）全報告PDF (7.4 MB)

Category:氣候變化

zh:政府間氣候變化專門委員會第四次評估報告 en:IPCC Fourth Assessment Report