全球變暖

全球變暖
維基百科，自由的百科全書http://zh.wikipedia.org/wiki/%E5%85%A8%E7%90%83%E6%9A%96%E5%8C%96
(重定向自全球暖化)
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為了閱讀方便，本文使用標題手工轉換。
·轉換標題為：中国大陆：全球变暖；台灣：全球暖化；香港：全球暖化
·實際標題為：全球变暖；當前顯示為：全球暖化
為了閱讀方便，本文使用全文手工轉換。轉換內容：
1.中国大陆：全球变暖；台灣：全球暖化；香港：全球暖化 當前用字模式下顯示為→全球暖化
2.中国大陆：弗吉尼亚；台灣：維吉尼亞；香港：維珍尼亞 當前用字模式下顯示為→維吉尼亞
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從1958年莫勞島二氧化碳含量變化
全球暖化指的是在一段時間中，地球的大氣和海洋溫度上升的現象，主要是指人為因素造成的溫度上升，原因很可能是由於溫室氣體排放過多造成的。
在20世紀，全球平均接近地面的大氣層溫度上升了攝氏0.6度。普遍來說，科學界認為過去五十年可觀察的氣候改變很可能是由人類活動所推動。
二氧化碳和其他溫室氣體的含量不斷增加，正是全球變暖的人為因素中主要部分。燃燒化石燃料、清理林木和耕作等等都增強了溫室效應。第一次懷疑溫室效應會發生的觀測是瑞典化學家阿累尼烏斯在1897年所做的。雖然當時沒有引發公眾討論，但是事隔90年，終於成了公眾關注的問題。
美國加利福尼亞大學的科學家在太平洋中央夏威夷的茂納羅亞峰上設立4個7米高和一個27米高的採樣塔，每小時採樣4次，分析二氧化碳的變化情況。（如右圖）[1][2]
目前全球平均溫度的變化，幾乎和二氧化碳含量的變化是同步上升的，從工業革命開始，二氧化碳的含量急劇增加，雖然植物的光合作用吸收了很大一部分二氧化碳，海洋也溶解一部分二氧化碳並固定成碳酸鈣，但空氣中二氧化碳的含量還是逐步增加。根據美國維吉尼亞大學和英國東安格裡亞大學聯合研究的結果，在進入20世紀後半葉，全球溫度上升的趨勢非常明顯，溫度變化情況見下圖。
全球性的溫度增量可能反過來導致其它方面的變動，包括海平面上升和降雨量及降雪量在數額上和樣式上的變化。這些變動也許促使極端天氣事件更強更頻繁，譬如洪水、旱災、熱浪、颶風和龍捲風。除此之外，還有其它後果，包括更高或更低的農產量、冰河撤退、夏天時河流流量減少、物種消失及疾病肆虐。預計全球變暖所因致事件的數量和強度; 但是很難把這些特殊事件連接到全球變暖。雖然很多研究集中在2100年或之前的時間，但是預期全球變暖、海平面上升會在往後的日子仍然繼續。因為二氧化碳在大氣中有50年到200年的壽命[3]。但是還是有不少氣候研究顯示為人類的行動在最近全球變暖中其實沒有扮演重要角色。可是, 更多人關心氣候變化在將來會是多少，而且對於應付預言後果的政策應該如何實施，正在展開一場熱烈的政治爭鬥和公開辯論。這些政策討論重點是應該減少還是扭轉未來的暖化及怎麼應付預計的後果。
目錄
[隐藏]
1 命名法則
2 歷史上的全球變暖
3 成因
3.1 大氣層中的溫室氣體
3.2 另外一些理論
3.2.1 太陽變化理論
4 造成的影響
5 對全球暖化的其他看法（各看法互相獨立）
6 參考文獻
7 參見
8 相關電影
9 外部連結
9.1 科學
9.2 兩極監察
9.3 其他
//
[編輯] 命名法則
全球變暖是比氣候改變更明確的名稱。原則上，「全球變暖」一詞對成因持中立觀點，但是根據大眾的用法，「全球變暖」意味著人類的影響。可是，聯合國氣候變化框架公約使用「氣候改變」代表人為因素導致的改變，「氣候變化」代表其他東西導致的改變。其他組織則使用「人為的氣候改變」（anthropogenic climate change）代表人為因素導致的改變。
[編輯] 歷史上的全球變暖
主條目：過去1000年的溫度記錄


根據不同的重組所展示過去2000年的平均地表溫度。每十年找一個平均值。特別顯示2004年的溫度來作參考。
根據儀器記錄，相對於1860年至1900年期間，全球陸地與海洋溫度上升了攝氏0.75度。自1979年，陸地溫度上升速度比海洋溫度快一倍（陸地溫度上升了攝氏0.25度，而海洋溫度上升了攝氏0.13度）。根據衛星溫度探測，對流層的溫度每十年上升攝氏0.12度至0.22度。在1850年前的一兩千年，雖然曾經出現中世紀溫暖時期與小冰河時期，但是大眾相信全球溫度是相對穩定的。
根據美國國家航空暨太空總署戈達德太空研究所的研究報告估計，自1800年代有測量儀器廣泛地應用開始，2005年是最溫暖的年份，比1998年的記錄高了攝氏百分之幾度。 世界氣象組織和英國氣候研究單位也有類似的估計，曾經預計2005年是僅次於1998年第二溫暖的年份。[4] [5]。
在人類近代歷史才有一些溫度記錄。這些記錄都來自不同的地方，精確度和可靠性都不盡相同。在1860年才有類似全球溫度儀器記錄，相信當年的記錄很少受到城市熱島效應的影響。從最近的千禧年內的多方記錄所展示的長遠展望，在過去1000年的溫度記錄中可以看到有關的討論及其中的差異。最近50年的氣候轉變的過程是十分清晰，全賴詳細的溫度記錄。到了1979年，人類更開始利用衛星溫度測量來量度對流層的溫度。
在2000年後，各地的高溫記錄經常被打破。譬如：2003年8月11日，瑞士格羅諾鎮錄得攝氏41.5度，破139年來的記錄。同年，8月10日，英國倫敦的溫度達到攝氏38.1，破了1990年的記錄。同期，巴黎南部晚上測得最低溫度為攝氏25.5度，破了1873年以來的記錄。8月7日夜間，德國也打破了百年最高氣溫記錄。在2003年夏天，台北、上海、杭州、武漢、福州都破了當地高溫記錄[6][7]，而中國浙江省更快速地屢破高溫記錄，67個氣象站中40個都刷新記錄。[8]2004年7月，廣州的罕見高溫打破了五十三年來的記錄。[9]2005年7月，美國有兩百個城市都創下歷史性高溫記錄。[10]2006年8月16日，重慶最高氣溫高達43度。[11]台灣宜蘭在2006年7月8日溫度高達38.8度，破了1997年的記錄。[12]2006年11月11日是香港整個十一月最熱的一日，最高氣溫高達29.2度，比1961年至1990年的平均最高溫26.1度還要高。[13]
[編輯] 成因
主條目：近代氣候轉變的成因和氣候轉變的科學觀點


過去40萬年的二氧化碳含量與自工業革命的急速飆升；地球軌道的週期性改變（又稱為米蘭柯維奇旋迴）被相信是十萬年的冰河時期循環的背後推動者。
氣候系統的改變來自自然或內部運作及對外來力量的改變作出的反應。這些外來力量包括了人為與非人為因素，譬如太陽活動、火山活動及溫室氣體。多名氣候學家同意地球近年來已經變暖。近代氣候轉變的成因仍然是活躍的研究範疇，但是科學界的共識指出溫室氣體是全球變暖的主因。可是，科學界外仍然對此結論有爭議。
在地球大氣層排放二氧化碳及甲烷，而其他情況不變下，會促使地面升溫，溫室氣體產生天然的溫室效應。如果沒有它，地球溫度會比現在低攝氏30度，使地球不適合人類居住。因此，在支持與反對這套變暖理論之間爭辯是不正確的，反而應該則重於大氣層中二氧化碳及甲烷含量的增加所產生的最終效果，什麼時候應該促進或什麼時候才同意使之緩和。
舉一個重要的回饋過程的例子，就是冰反照率回饋。大氣層中增加二氧化碳暖化了地球表面，導致兩極冰塊溶解。陸地與開放水域便佔據更多的地方。兩者比冰的反射還要少，所以吸收了更多太陽輻射。這樣使變暖加劇，到頭來促使更多冰塊溶化，循環不斷持續。
因為地球的熱力慣性與對其他間接效應的緩慢反應，地球現今的氣候在不斷增加的溫室氣體下變得不平衡。氣候行為研究指出，縱使溫室氣體維持現今的水準，全球平均溫度可能仍然會上升攝氏0.5至1度。
[編輯] 大氣層中的溫室氣體


在過去65萬年，大氣層二氧化碳與全球溫度的圖表


1980年至2003年，全球主要溫室氣體的趨勢圖
溫室氣體對於太陽的短波輻射來說是透明的。可是，它們卻吸收了來自地球發放的（黑體輻射）部份長波的紅外線輻射。這樣使地球難以降溫。它們能暖化地球多少是以全球暖化勢能作指標。
大氣層中二氧化碳及甲烷的濃度自1750年比前工業化水平（280百萬分率）分別上升了31%與149%。而現在的水平已經高於380百萬分率。從冰芯中提取可靠的數據指出，與過去65萬年的作比較，這是個明顯的飆升。從一些非直接的地質學證據，有理由相信過去4千萬年的二氧化碳含量比較高。在過去的二十年中，大約四分之三的人為的二氧化碳排放都是燃燒化石燃料。其他的人為排放都是土地使用方面，特別是砍伐森林。[14]
1958年在夏威夷大島海拔約3400公尺的毛納洛峰上對二氧化碳混合比率展開了最漫長的連續的儀器測量。從此以後，人們發現每年的測量結果不斷攀升，如基林曲線（Keeling Curve）顯示，數值由當初的315百萬分率上升至2006年超過了380百萬分率，升幅大約是21%。[15][16]結果顯示二氧化碳含量在每個月出現輕微季節性變動而整體上全年是不斷上升。
甲烷是天然氣的主要組成部分，大部分由生物生產和從天然氣管道和其它基礎設施洩漏出來。一些甲烷的生物來源是自然的，譬如白蟻。可是其他來源則是由人類農業活動增加而帶動的，例如稻米的耕種。[17]最近的證據顯示，森林也許是甲烷的來源[18][19]。如果屬實，這會是對天然溫室效應的額外貢獻，而不是人為溫室效應的。[20]
雖然實際的趨勢軌線視乎不確定的經濟、社會、科技及自然發展，預期未來的二氧化碳水平將因為使用化石燃料而持續攀升。政府間氣候變化委員會的《排放情況的特殊報告》羅列出很多不同的二氧化碳情況，在2100年可以達致由541至970百萬分率的水平。[21]如果煤與焦油被廣泛地採用，現時的化石燃料儲備是有能力實現這個水平並且在2100年後繼續排放。


於2000年人為排放的溫室氣體的各個組成部分
全球的主要人為排放的溫室氣體是來自燃燒燃料。餘下的大部分來自「短暫的燃料」（生產與運送中耗用的燃料）、工業及農業生產中的排放。在1990年，他們的比重分別是5.8%、5.2%和3.3%。當前的數據都可以作比較。[22]大約17%來自發電時所耗用的燃料。很少來自大自然與人為生物來源，大約只有6.3%來自農業所產生的甲烷和氧化亞氮。
正迴饋效果會導致更多溫室氣體的來源。譬如從西伯利亞永久凍土中的泥煤田釋放的甲烷可能多達7百億噸。 [23]注意人類排放的污染物如硫酸鹽氣溶膠有冷卻的作用。雖然被干擾的自然循環可能導致二十世紀中期的溫度記錄中所見的高原，但那些人類排放的污染物在某個程度上也引致同樣的溫度記錄[24]
[編輯] 另外一些理論
人類曾企圖測量關於「在過去50年觀察得到的大部分暖化都是由人類活動所致的」的科學公眾輿論程度。 [25]　在科學雜誌中，加州聖迭戈大學的歷史學教授納奧秘·奧勒斯克斯從科學資訊機構中的928份科學文獻的摘要中尋找全球氣候改變（global climate change）。他得出結論，當中75%明示或暗示接受了這個公眾輿論的觀點。[26][27]可是，奧勒斯克斯教授並沒有表示幾多摘要指出人類導致的暖化效果。
除了這個公眾輿論外，還有其他的假說嘗試解釋全部或部分的全球溫度升高的原因。某些假說如下：
· 全球溫度升高仍然屬於自然溫度變化的範圍之內。
· 全球溫度升高是小冰河時期的來臨。
· 全球溫度升高的原因是太陽輻射的變化及雲層覆蓋的調節效果。[28]
· 全球溫度升高正反映了城市熱島效應。因為很多讀數都在人口稠密或正在擴張的地區。[29]
[編輯] 太陽變化理論


過去30年的太陽輻射的變化圖
政府間氣候變化專門委員會的第三份評估報告所闡述的模型研究發現最近40至50年的氣候改變並不需要太陽發光度的變動。[30]這些研究發現火山及太陽活動只能影響1950年前的溫度改變的一半，但這種自然力量最近已經被抵消。[31]特別是，自1750年的溫室氣體所推動的氣候改變比同期增加的太陽活動所推動的高出八倍。[32]
有些研究（Lean等人，2002年；Wang等人，2005年）認為前工業時期的太陽發光度比第三份評估報告中所提及的復原紀錄（例如:Hoyt和Schatten，1993年；Lean，2000年）還少三四倍。其他研究人員[33]相信太陽發光度對全球變暖的影響被低估了。他們估計太陽活動促使近來溫室效應的16%或36%。其它人[34]則建議雲層和其他過程的回饋加劇了太陽活動的變動所帶來的影響。如果是真的，太陽活動的變動真的被低估了。從普遍的科學理解來說，太陽發光度變動對歷史上的氣候改變貢獻是十分小[6]。
現在的太陽活動水準是歷史性高。科學家Sami Solanki博士等人認為過去60年至70年的太陽活動是八千年來的高峰期。[35]Muscheler等人則認為過去幾千年都曾經出現類似的高峰期。[36]Solanki博士根據他們的分析斷定了太陽活動在未來的50年會降低的機會率大約是92%。再者，美國杜克大學的研究者在2005年發現過去二十年的改變中的10%至30%可能來自增加的太陽輸出。[37]回顧了現有的文獻，Foukal等人斷定自從1970年代中期太陽輸出的變化很難加劇全球變暖並且沒有證據顯示太陽發光度在這個時期有所增加。[38][39]
[編輯] 造成的影響
主條目：全球暖化的效應


一千年內北半球溫度變化趨勢（1000年-1950年每50年一刻度，1950-2000每10年一刻度）
1. 由於海洋溫度增加，南極和北極的冰川會加速融化，導致海平面上升，會淹沒沿海低海拔地區，例如大洋洲島國圖瓦魯已被水淹沒。全世界有3/4的人口居住在離海岸線不足500公里的地方，陸地面積縮小會極大地影響人類居住環境，甚至可能導致戰爭。
2. 由於海洋溫度增加，水蒸發加快，大量水氣被輸送進入大氣，會導致局部地區短時間內降雨量突然升高，這樣暴雨天氣就會導致水災、山體滑坡、泥石流等更加頻繁的發生，位於河流沿岸的城市和位於河流下游的廣大地區因此受到洪水的威脅，水災面積因為短時的強降水而迅速擴大，水土流失問題也比過去更加嚴峻。
3. 由於大氣溫度升高，導致熱帶傳染病向高緯擴散，目前已有熱帶傳染病擴散的跡象。而過去在低溫下難以存活的病毒隨著冬季溫度上升，有全年活動的可能，最近一段時間的監控發現，過去已經得到控制的疾病如結核病等有再度爆發的可能。
4. 由於大氣溫度升高，令蒸發量上升，在以往乾旱少雨的地區面臨更加嚴峻的考驗，而不正確的耕作方法很有可能讓以前植被覆蓋就不好的半乾旱地區失去保護成為半沙化地區，從而導致內陸地區沙漠化加速，沙漠有擴大的危險（實際上沙漠化問題已經困擾著東亞和中亞國家，在撒哈拉邊界地區更是情況堪憂）。
5. 雖然由於溫度升高，有部分動植物會加快繁殖，而如果食物鏈中的上層和頂層生物如果不作出相應變動就會嚴重危機到種群的繁殖和發展，整個生物多樣性(Biodiversity)會受到威脅，許多物種會加速滅絕的步伐。
6. 由於兩極冰山崩塌，北歐、南美近極地的地方溫度會迅速下降，會嚴重影響當地生態系統，造成不可逆的變化。
全球暖化可能極大地影響人類生存環境，人類應該起碼將自己對全球暖化的貢獻降到最低程度，盡量減緩全球暖化的趨勢。

[編輯] 對全球暖化的其他看法（各看法互相獨立）
1. 現在的時代是地質史上相對比較寒冷的時代，地質史上曾有的地球氣溫達攝氏80多度[來源請求]，恰是生物繁盛的時代，全球暖化有助於生態系統的更加穩定。
2. 全球暖化將使全球熱量上升，使得農作物的播種範圍擴大，再加上空氣中二氧化碳濃度增高，空氣中的水氣增加，有利於降水，所有這些因素，有利於農業的發展。
3. 否認全球暖化的：近幾十年來，全球平均氣溫波動均在0.6攝氏度以內。這麼小的氣溫變率是正常現象。
4. 全球暖化起因於城市熱島效應，由於城市的氣溫上升，位於都市的氣溫觀測當然會上升，因此高估了實際上的全球溫度上升。
5. 認為全球暖化不是二氧化碳成因的，二氧化碳在大氣中的溫室效應有待進一步評估, 因為水氣才使主要的溫室氣體(60~70%),但是二氧化碳只有26%。
6. 與其採用限制二氧化碳排放的方法來控制全球暖化，還不如利用其他方法來解決全球暖化造成的問題；這樣才能有效的利用資源。
[編輯] 參考文獻
1. ↑ （英文）Carbon dioxide in the atmosphere - first signs of increase
2. ↑ 茂納羅亞峰上採集的數據
3. ↑ 美國環保局:全球變暖潛力與大氣中壽命
4. ↑ 美國國家航空暨太空總署戈達德太空研究所的研究報告全球溫度趨勢
5. ↑ 2005年的溫度
6. ↑ 天氣在線：入夏以來中國和歐洲的高溫記錄
7. ↑ [http://unn.people.com.cn/BIG5/22220/28976/28982/1991868.html 人民網:武漢又創高溫記錄 昨日百年最熱一天]
8. ↑ 湖南新聞網:浙江高溫記錄不斷刷新 成為全國最熱地區之一
9. ↑ 大紀元:廣州出現五十三年來罕見高溫
10. ↑ 美國兩百個城市單日高溫創歷史記錄
11. ↑ 新華網:重慶創高溫記錄 南方各地暑熱難耐
12. ↑ 宜蘭出現焚風 高溫破入夏記錄：38.8度
13. ↑ 都市日報:11月平均溫度 創120年高溫紀錄
14. ↑ 2001年氣候改變的科學基礎
15. ↑ 地球系統研究實驗室:環球監察科
16. ↑ 地球系統研究實驗室:環球監察科:消息公告
17. ↑ 聯合國政府間氣候變化專門委員會:2001年的科學數據
18. ↑ 真實氣候
19. ↑ BBC新聞:發現植物也釋放甲烷
20. ↑ Ealert
21. ↑ [1]
22. ↑ 溫室氣體資料庫
23. ↑ 英國衛報:全球變暖命中「打翻點」
24. ↑ http://www.grida.no/climate/ipcc_tar/wg1/462.htm
25. ↑ http://www.grida.no/climate/ipcc_tar/wg1/007.htm
26. ↑ http://www.realclimate.org/index.php?p=80
27. ↑ 科學雜誌: The Scientific Consensus on Climate Change
28. ↑ 丹麥國家太空中心
29. ↑ ReasonOnline:Stars in Her Eyes
30. ↑ 政府間氣候變化專門委員會的第三份評估報告:第11章第2節
31. ↑ 政府間氣候變化專門委員會的第三份評估報告:第11章第4節
32. ↑ 政府間氣候變化專門委員會的第三份評估報告:第6章第13節
33. ↑ 彼得·A·史托等人在2003年的研究[2]
34. ↑ Marsh and Svensmark 2000 [3]
35. ↑ 產業溫室氣體排放管理及輔導計畫網站:溫室氣體減量電子報-第7期
36. ↑ [4]
37. ↑ 杜克大學物理學家報告
38. ↑ 《自然》雜誌9月18日內容精選
39. ↑ [5]
[編輯] 參見
· 全球暖化的效應
· 大氣層
· 政府間氣候變化專門委員會
· 北極氣候影響評估報告
[編輯] 相關電影
· 明天過後
· 不願面對的真相
· 未來水世界
· 日本沉沒
[編輯] 外部連結
[編輯] 科學
· 1995年諾貝爾化學獎獲得者駱嵐教授訪問:全球變暖和臭氧耗盡
· 莫勞島二氧化碳含量變化
· 長春社
· 氣候轉變
· 海洋及氣候改變協會的全球變暖資訊, 伍茲霍爾海洋研究院 (Woods Hole Oceanographic Institution)
· 政府間氣候變化專門委員會(IPCC)
o 政府間氣候變化專門委員會第三個評估報告 於2001年刊登
o 政府間氣候變化專門委員會第二工作組(衝擊、適應和弱點)氣候改變2001
o 政府間氣候變化專門委員會報告摘要 - GreenFacts編輯
· 美國國家航空暨太空總署全球水文學和氣候中心
· 夏威夷Mauna Loa Observatory - 最近二氧化碳含量的測量與數據
· 聯合國環保計劃中有關全球變暖的地圖
· 國家海洋與大氣管理局全球變暖的答客問
· 真實氣候 - 一群氣候科學家的網誌
· 國家大氣層研究中心 - 氣候改變研究總覽
· 德國波茨坦氣候影響研究所
· 發現全球變暖 發現過程的詳盡介紹與歷史
· 氣候改變的介紹:氣象學家的筆記 (世界氣象組織) (PDF)
· Pew研究中心
· 國家海洋與大氣管理局地球系統實驗室全球監測組
· 全球變暖, 美國環境保護署
· 美國氣候改變科學計劃的最後報告
· 西伯利亞溶解中的湖水釋放了溫室氣體
· 丹麥國家太空中心:天空實驗
· 全球變暖網站
· 氣候科學監測
[編輯] 兩極監察
· 永久凍土如何快速改變？這些改變又有什麼衝擊？
· NOAA
· 俄羅斯永久凍土的溶解可能加速了全球變暖[7]
[編輯] 其他
· 專門委員會報告：關於「曲棍球球棍」重建全球性氣候
· 氣候方舟 - 提供新聞及分析的氣候改變及全球變暖的入門網站
· Science and Technology Librarianship: Global Warming and Climate Change Science — Extensive commented list of Internet resources — Science and Technology Sources on the Internet.
· Union of Concerned Scientists Global Warming page
· BBC: Global warming risk 'much higher'
· Watch and read 'Tipping Point', Australian science documentary about effects of global warming on rare, common, and endangered wildlife
· Summary by "Physicians and Scientists for Responsible Application of Science and Technology"
· A report by the Competitive Enterprise Institute, a pro-business group of global warming skeptics
· Newest reports on US EPA website
· An optimistic outlook on Global Warming from PBNV.com Apr 25, 2006
· The Discovery of Global Warming from historian Spencer Weart, Director of the Center for History of Physics of the American Institute of Physics (AIP).
· IPS Inter Press Service - Independent news on global warming and its consequences.
Template:UATemplate:UATemplate:UAzh:全球暖化
取自"http://zh.wikipedia.org/w/index.php?title=%E5%85%A8%E7%90%83%E5%8F%98%E6%9A%96&variant=zh-tw"
2個分類: 地球科學 | 氣候變化
National Oceanic and Atmospheric Administration
Global Warming
Frequently Asked Questions
http://www.ncdc.noaa.gov/oa/climate/globalwarming.html


Please note that this page is in the process of being updated with new information from the Fourth IPCC Assessment and other recent work. Please check back frequently for changes.

· Introduction
· What is the greenhouse effect, and is it affecting our climate?
· Are greenhouse gases increasing?
· Is the climate warming?
· Are El Niños related to Global Warming?
· Is the hydrological cycle (evaporation and precipitation) changing?
· Is the atmospheric/oceanic circulation changing?
· Is the climate becoming more variable or extreme?
· How important are these changes in a longer-term context?
· Is sea level rising?
· Can the observed changes be explained by natural variability?
· What about the future?
· Additional Information
http://www.nrdc.org/globalWarming/f101.asp
Global Warming Basics What it is, how it's caused, and what needs to be done to stop it. [En Español]
What causes global warming?
Is the earth really getting hotter?
Are warmer temperatures causing bad things to happen?
Is global warming making hurricanes worse?
Is there really cause for serious concern?
Could global warming trigger a sudden catastrophe?
What country is the largest source of global warming pollution?
How can we cut global warming pollution?
Why aren't these technologies more commonplace now?
Do we need new laws requiring industry to cut emissions of global warming pollution?
Is it possible to cut power plant pollution and still have enough electricity?
How can we cut car pollution?
What can I do to help fight global warming?
Consequences of Global Warming Unless we act now, our children will inherit a hotter world, dirtier air and water, more severe floods and droughts, and more wildfires [En Español]

(See more Google Earth maps.)









ALASKA HEATS UPWarming temperatures are already having an impact on the people, wildlife and landscape of Alaska. Click on the numbers on this map to see what's happening on the front lines of global warming.
1. Barrow 2. Shismaref 3. Yukon River 4. Wasilla 5. Kenai Peninsula 6. McCall Glacier 7. Fairbanks
The latest scientific data confirm that the earth's climate is rapidly changing. Global temperatures increased by about 1 degree Fahrenheit over the course of the last century, and will likely rise even more rapidly in coming decades. The cause? A thickening layer of carbon dioxide pollution, mostly from power plants and automobiles, that traps heat in the atmosphere.
Scientists say that unless global warming emissions are reduced, average U.S. temperatures could rise another 3 to 9 degrees by the end of the century -- with far-reaching effects. Sea levels will rise, flooding coastal areas. Heat waves will be more frequent and more intense. Droughts and wildfires will occur more often. Disease-carrying mosquitoes will expand their range. And species will be pushed to extinction. As this page shows, many of these changes have already begun.

CLIMATE PATTERN CHANGES
Consequence: warmer temperaturesAverage temperatures will rise, as will the frequency of heat waves.
Warning signs today
Most of the United States has already warmed, in some areas by as much as 4 degrees Fahrenheit. In fact, no state in the lower 48 states experienced below average temperatures in 2002. The last three five-year periods are the three warmest on record.
Many places in North America had their hottest seasons or days on record in the late 1990s.
Since 1980, the earth has experienced 19 of its 20 hottest years on record, with 2005 and 1998 tied for the hottest and 2002 and 2003 coming in second and third.
Consequence: drought and wildfireWarmer temperatures could also increase the probability of drought. Greater evaporation, particularly during summer and fall, could exacerbate drought conditions and increase the risk of wildfires.
Warning signs today
Greater evaporation as a result of global warmingcould increase the risk of wildfires.
The 1999-2002 national drought was one of the three most extensive droughts in the last 40 years.
In 2002, the Western United States experienced its second worst wildfire season in the last 50 years; more than 7 million acres burned. Colorado, Arizona, and Oregon had their worst seasons.
The period from April through June of 1998 was the driest three-month period in 104 years in Florida, Texas, and Louisiana.
Dry conditions produced the worst wildfires in 50 years in Florida in 1998.
April through July of 1999 was the driest four-month stretch in 105 years of record-keeping in New Jersey, Delaware, Maryland, and Rhode Island.
Montana, Colorado, and Kansas experienced severe dust storms in 2002, a product of dry conditions.
September 2001 to February 2002 was the second driest six-month period on record for the Northeast.
Consequence: more intense rainstormsWarmer temperatures increase the energy of the climatic system and lead to more intense rainfall at some times and in some areas.
Warning signs today
National annual precipitation has increased between 5 and 10 percent since the early 20th century, largely the result of heavy downpours in some areas.
Vermont, New Hampshire, Rhode Island, and Massachusetts each got more than double their normal monthly rainfall in June 1998.
Severe flooding in the Texas, Montana, and North Dakota during the summer of 2002 caused hundreds of millions of dollars in damage.

HEALTH EFFECTS
More frequent and more intensive heat waves could result in more heat-related deaths. Photo: Gary Braasch, Chicago, July 1995. See the World View of Global Warming website for more Gary Braasch photos illustrating the consequences of the changing climate.
Consequence: deadly heat waves and the spread of diseaseMore frequent and more intensive heat waves could result in more heat-related deaths. These conditions could also aggravate local air quality problems, already afflicting more than 80 million Americans. Global warming is expected to increase the potential geographic range and virulence of tropical diseases as well.
Warning signs today
In 2003, extreme heat waves caused more than 20,000 deaths in Europe and more than 1500 deaths in India.
More than 250 people died as a result of an intense heat wave that gripped most of the eastern two-thirds of the United States in 1999.
Disease-carrying mosquitoes are spreading as climate shifts allow them to survive in formerly inhospitable areas. Mosquitoes that can carry dengue fever viruses were previously limited to elevations of 3,300 feet but recently appeared at 7,200 feet in the Andes Mountains of Colombia. Malaria has been detected in new higher-elevation areas in Indonesia.

WARMING WATER
Consequence: more powerful and dangerous hurricanesWarmer water in the oceans pumps more energy into tropical storms, making them more intense and potentially more destructive.
Warning signs today
The number of category 4 and 5 storms has greatly increased over the past 35 years, along with ocean temperature.
Consequence: melting glaciers, early ice thawRising global temperatures will speed the melting of glaciers and ice caps, and cause early ice thaw on rivers and lakes.
Warning signs today
At the current rate of retreat, all of the glaciers in Glacier National Park will be gone by 2070.
After existing for many millennia, the northern section of the Larsen B ice shelf in Antarctica -- a section larger than the state of Rhode Island -- collapsed between January and March 2002, disintegrating at a rate that astonished scientists. Since 1995 the ice shelf's area has shrunk by 40 percent.
According to NASA, the polar ice cap is now melting at the alarming rate of nine percent per decade. Arctic ice thickness has decreased 40 percent since the 1960s.
In 82 years of record-keeping, four of the five earliest thaws on Alaska's Tanana River were in the 1990s.
The satellite photo at far left shows the Larson B ice shelf on Jan. 31, 2002. Ice appears as solid white. Moving to the right, in photos taken Feb. 17 and Feb. 23, the ice begins to disintegrate. In the photos at far right, taken Mar. 5 and Mar 7, note water (blue) where solid ice had been, and that a portion of the shelf is drifting away. Photos: National Aeronautics and Space Administration
Consequence: sea-level riseCurrent rates of sea-level rise are expected to increase as a result both of thermal expansion of the oceans and of partial melting of mountain glaciers and the Antarctic and Greenland ice caps. Consequences include loss of coastal wetlands and barrier islands, and a greater risk of flooding in coastal communities. Low-lying areas, such as the coastal region along the Gulf of Mexico and estuaries like the Chesapeake Bay, are especially vulnerable.
Warning signs today
The current pace of sea-level rise is three times the historical rate and appears to be accelerating.
Global sea level has already risen by four to eight inches in the past century. Scientists' best estimate is that sea level will rise by an additional 19 inches by 2100, and perhaps by as much as 37 inches.

ECOSYSTEM DISRUPTION
Warmer temperatures may cause some ecosystems, including alpine meadows in the Rocky Mountains, to disappear.
Consequence: ecosystem shifts and species die-offThe increase in global temperatures is expected to disrupt ecosystems and result in loss of species diversity, as species that cannot adapt die off. The first comprehensive assessment of the extinction risk from global warming found that more than one million species could be committed to extinction by 2050 if global warming pollution is not curtailed. Some ecosystems, including alpine meadows in the Rocky Mountains, as well as tropical montane and mangrove forests, are likely to disappear because new warmer local climates or coastal sea level rise will not support them.
Warning signs today
A recent study published in the prestigious journal Nature found that at least 279 species of plants and animals are already responding to global warming. Species' geographic ranges have shifted toward the poles at an average rate of 4 miles per decade and their spring events have shifted earlier by an average of 2 days per decade.
In Washington's Olympic Mountains, sub-alpine forest has invaded higher elevation alpine meadows. In Bermuda and other places, mangrove forests are being lost.
In areas of California, shoreline sea life is shifting northward, probably in response to warmer ocean and air temperatures.
Over the past 25 years, some penguin populations have shrunk by 33 percent in parts of Antarctica, due to declines in winter sea-ice habitat.
Related NRDC WebpagesArctic on Thin IceGlobal Warming in the Arctic and AntarcticGlobal Warming Threatens FloridaBibliography of Climate Studies
Related WebsitesIntergovernmental Panel on Climate ChangeUnion of Concerned Scientists, California's Climate ChoicesNational Climatic Data CenterGlobal Warming: Early Warning Signs MapU.S. National Assessment of the Potential Consequences of Climate Variability and Change
last revised 1.9.06


Take Online Action Now!
Tell Congress to get serious about stopping global warming.
Tell your representative to raise fuel efficiency standards now.
In the News
US Not Prepared for Peril from Global WarmingNRDC Media Center
Multi-State Compact to Fight Global Warming Expands Once AgainNRDC Media Center
More press releases on global warming
Related Stories
Step It UpPhotos and videos from Step It Up rallies around the United States, April 14, 2007.
Legislation to Control Global Warming PollutionThe United States must pass strong legislation to cap emissions of heat-trapping pollutants.
Related Links
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Contents/Site Map June 2006 version
About this site: TOP OF PAGE Summary of the History of Climate Change Science SEARCH all the essays

Climate data The Modern Temperature Trend Past Cycles: Ice Age Speculations Temperatures from Fossil Shells Rapid Climate Change Uses of Radiocarbon Dating Greenland Ice Drilling (J. Genuth) Influences on climateThe Carbon Dioxide Greenhouse Effect Roger Revelle's Discovery Other Greenhouse Gases Aerosols: Effects of Haze and Cloud Biosphere: How Life Alters ClimateChanging Sun, Changing Climate? Interview with Jack EddyOcean Currents and ClimateTheorySimple Models of Climate Change Chaos in the Atmosphere Venus & Mars General Circulation Models Basic Radiation Calculations Arakawa's Computation Device GCM Family Tree (P. Edwards)
About this site History in Hypertext - Methodology & SourcesList of illustrations Please contribute comments, corrections.Author, Spencer Weart
Social relationshipsThe Public and Climate Change (1) (2) Wintry Doom Ice Sheets and Rising SeasGovernment: The View from Washington Climate Modification Schemes Money for Keeling: Monitoring CO2 Levels International Cooperation Climatology as a Profession
Reflections on the Scientific Process A Personal Note Talking Points (pdf)
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This is mounted on the Web site of the Center for History of Physics of the American Institute of Physics.Discovery of Global Warming site created by Spencer Weart with support from the American Institute of Physics, the National Science Foundation and the Alfred P. Sloan Foundation. Copyright © 2003-2006 Spencer Weart and the American Institute of Physics.Index terms: climate change, global warming, greenhouse effect, temperature change, history, science, geophysics, meteorology, computer models, aerosols, ice. Book cover photo by Frank Cezus © Getty Images.
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Global warming
From Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Global_warming
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Global mean surface temperature anomaly 1850 to 2006 relative to 1961–1990


Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980
Global warming is the increase in the average temperature of the Earth's near-surface air and oceans in recent decades and its projected continuation.
Global average air temperature near the Earth's surface rose 0.74 ± 0.18 °C (1.3 ± 0.32 °F) during the past century. The Intergovernmental Panel on Climate Change (IPCC) concludes, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations,"[1] which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Natural phenomena such as solar variation combined with volcanoes have probably had a small warming effect from pre-industrial times to 1950, but a small cooling effect since 1950.[2][3] These basic conclusions have been endorsed by at least 30 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries. The American Association of Petroleum Geologists is the only scientific society that rejects these conclusions.[4][5] A few individual scientists disagree with some of these conclusions as well.[6]
Climate models referenced by the IPCC project that global surface temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100.[1] The range of values reflects the use of differing scenarios of future greenhouse gas emissions and results of models with differences in climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if greenhouse gas levels are stabilized. [1] This reflects the large heat capacity of the oceans.
An increase in global temperatures can in turn cause other changes, including sea level rise, and changes in the amount and pattern of precipitation resulting in floods and drought[7]. There may also be changes in the frequency and intensity of extreme weather events, though it is difficult to connect specific events to global warming. Other effects may include changes in agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors.
Remaining scientific uncertainties include the exact degree of climate change expected in the future, and how changes will vary from region to region around the globe. There is ongoing political and public debate regarding what, if any, action should be taken to reduce or reverse future warming or to adapt to its expected consequences. Most national governments have signed and ratified the Kyoto Protocol aimed at combating greenhouse gas emissions.
Contents
[hide]
1 Terminology
2 Causes
2.1 Greenhouse gases in the atmosphere
2.2 Feedbacks
2.3 Solar variation
3 History
3.1 From the present to the dawn of human settlement
3.2 Pre-human climate variations
4 Climate models
5 Attributed and expected effects
5.1 Economics
6 Mitigation and adaptation
7 Issue debate and political processes
8 Related climatic issues
9 See also
10 References
11 Further reading
12 External links
12.1 Scientific
12.2 Educational
12.3 Other
//
Terminology
The term "global warming" is a specific example of the broader term climate change, which can also refer to global cooling. In common usage the term refers to recent warming and implies a human influence.[8] The United Nations Framework Convention on Climate Change (UNFCCC) uses the term "climate change" for human-caused change, and "climate variability" for other changes.[9] The term "anthropogenic climate change" is sometimes used when focusing on human-induced changes.
Causes


Carbon dioxide during the last 400,000 years and (inset above) the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.
Main articles: Attribution of recent climate change and scientific opinion on climate change
The climate system varies through natural, internal processes and in response to variations in external forcing factors including solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming remain an active field of research, but the scientific consensus [10] identifies increased levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available. Contrasting with the scientific consensus, other hypotheses have been proposed to explain most of the observed increase in global temperatures. One such hypothesis is that the warming is caused by natural fluctuations in the climate or that warming is mainly a result of variations in solar radiation. [11]
None of the effects of forcing are instantaneous. Due to the thermal inertia of the Earth's oceans and slow responses of other indirect effects, the Earth's current climate is not in equilibrium with the forcing imposed. Climate commitment studies indicate that even if greenhouse gases were stabilized at present day levels, a further warming of about 0.5 °C (0.9 °F) would still occur. [12]
Greenhouse gases in the atmosphere
Main article: Greenhouse effect


Recent increases in atmospheric carbon dioxide (CO2). The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring, and declines during the northern hemisphere growing season as plants remove some CO2 from the atmosphere.
The greenhouse effect was discovered by Joseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896. It is the process by which absorption and emission of infrared radiation by atmospheric gases warms a planet's atmosphere and surface.
Greenhouse gases create a natural greenhouse effect, without which mean temperatures on Earth would be an estimated 30 °C (54 °F) lower so that Earth would be uninhabitable.[13] Thus scientists do not "believe in" or "oppose" the greenhouse effect as such; rather, the debate concerns the net effect of the addition of greenhouse gases, while allowing for associated positive and negative feedback mechanisms.
On Earth, the major natural greenhouse gases are water vapor, which causes about 36–70% of the greenhouse effect (not including clouds); carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone, which causes 3–7%. Some other naturally occurring gases contribute very small fractions of the greenhouse effect; one of these, nitrous oxide (N2O), is increasing in concentration owing to human activity such as agriculture. The atmospheric concentrations of CO2 and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750. These levels are considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that CO2 values this high were last attained 20 million years ago.[14] "About three-quarters of the anthropogenic [man-made] emissions of CO2 to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation."[15]
The present atmospheric concentration of CO2 is about 383 parts per million (ppm) by volume.[16] Future CO2 levels are expected to rise due to ongoing burning of fossil fuels and land-use change. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels. The IPCC Special Report on Emissions Scenarios gives a wide range of future CO2 scenarios, ranging from 541 to 970 ppm by the year 2100.[17] Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal, tar sands or methane clathrates are extensively used.[18]
Positive feedback effects such as the expected release of CH4 from the melting of permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes) may lead to significant additional sources of greenhouse gas emissions[19] not included in climate models cited by the IPCC.[1]
Feedbacks
Main article: Effects of global warming#Further global warming (positive feedback)
The effects of forcing agents on the climate are complicated by various feedback processes.
One of the most pronounced feedback effects relates to the evaporation of water. CO2 injected into the atmosphere causes a warming of the atmosphere and the earth's surface. The warming causes more water to be evaporated into the atmosphere. Since water vapor itself acts as a greenhouse gas, this causes still more warming; the warming causes more water vapor to be evaporated, and so forth until a new dynamic equilibrium concentration of water vapor is reached at a slight increase in humidity and with a much larger greenhouse effect than that due to CO2 alone.[20] This feedback effect can only be reversed slowly as CO2 has a long average atmospheric lifetime.
Feedback effects due to clouds are an area of ongoing research and debate. Seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect. Seen from above, the same clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Increased global water vapor concentration may or may not cause an increase in global average cloud cover. The net effect of clouds thus has not been well modeled, however, cloud feedback is second only to water vapor feedback and is positive in all the models that contributed to the IPCC Fourth Assessment Report.[20]
Another important feedback process is ice-albedo feedback.[21] The increased CO2 in the atmosphere warms the Earth's surface and leads to melting of ice near the poles. As the ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice, and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues.
Positive feedback due to release of CO2 and CH4 from thawing permafrost is an additional mechanism contributing to warming. Possible positive feedback due to CH4 release from melting seabed ices is a further mechanism to be considered.
The ocean's ability to sequester carbon is expected to decline as it warms, because the resulting low nutrient levels of the mesopelagic zone limits the growth of diatoms in favour of smaller phytoplankton that are poorer biological pumps of carbon.[22]
Solar variation


Solar variation over the last 30 years.
Main article: Solar variation
Variations in solar output, possibly amplified by cloud feedbacks, may have contributed to recent warming.[23] A difference between this mechanism and greenhouse warming is that an increase in solar activity should produce a warming of the stratosphere while greenhouse warming should produce a cooling of the stratosphere. Reduction of stratospheric ozone also has a cooling influence but substantial ozone depletion did not occur until the late 1970s. Cooling in the lower stratosphere has been observed since at least 1960.[24] Thus, solar activity alone is not the main contributor to recent warming.
Phenomena such as solar variation combined with volcanoes have probably had a warming effect from pre-industrial times to 1950, but a cooling effect since 1950.[1] However, some research has suggested that the Sun's contribution may have been underestimated. Two researchers at Duke University have estimated that the Sun may have contributed about 40–50% of the global surface temperature warming over the period 1900–2000, and about 25–35% between 1980 and 2000.[25] Stott and coauthors suggest that climate models overestimate the relative effect of greenhouse gases compared to solar forcing; they also suggest that the cooling effects of volcanic dust and sulfate aerosols have been underestimated.[26] Nevertheless, they conclude that even with an enhanced climate sensitivity to solar forcing, most of the warming during the latest decades is attributable to the increases in greenhouse gases.
History


Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume. Today's date is on the left side of the graph.
Main article: Temperature record
From the present to the dawn of human settlement
Global temperatures on both land and sea have increased by 0.75 °C (1.4 °F) relative to the period 1860–1900, according to the instrumental temperature record. This measured temperature increase is not significantly affected by the urban heat island. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).[27] Temperatures in the lower troposphere have increased between 0.12 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with possibly regional fluctuations such as the Medieval Warm Period or the Little Ice Age.
Based on estimates by NASA's Goddard Institute for Space Studies, 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree.[28] Estimates prepared by the World Meteorological Organization and the Climatic Research Unit concluded that 2005 was the second warmest year, behind 1998.[29][30]
Anthropogenic emissions of other pollutants—notably sulfate aerosols—can exert a cooling effect by increasing the reflection of incoming sunlight. This partially accounts for the cooling seen in the temperature record in the middle of the twentieth century,[31] though the cooling may also be due in part to natural variability.
Paleoclimatologist William Ruddiman has argued that human influence on the global climate began around 8,000 years ago with the start of forest clearing to provide land for agriculture and 5,000 years ago with the start of Asian rice irrigation.[32] Ruddiman's interpretation of the historical record, with respect to the methane data, has been disputed.[33]
Pre-human climate variations


Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.
Further information: Paleoclimatology
See also: Snowball Earth
Earth has experienced warming and cooling many times in the past. The recent Antarctic EPICA ice core spans 800,000 years, including eight glacial cycles timed by orbital variations with interglacial warm periods comparable to present temperatures.[34]
A rapid buildup of greenhouse gases caused warming in the early Jurassic period (about 180 million years ago), with average temperatures rising by 5 °C (9.0 °F). Research by the Open University indicates that the warming caused the rate of rock weathering to increase by 400%. As such weathering locks away carbon in calcite and dolomite, CO2 levels dropped back to normal over roughly the next 150,000 years.[35][36]
Sudden releases of methane from clathrate compounds (the clathrate gun hypothesis) have been hypothesized as a cause for other warming events in the distant past, including the Permian-Triassic extinction event (about 251 million years ago) and the Paleocene-Eocene Thermal Maximum (about 55 million years ago).
Climate models


The projected temperature increase for a range of stabilization scenarios (the coloured bands). The black line in middle of the shaded area indicates 'best estimates'; the red and the blue lines the likely limits. From the work of IPCC AR4, 2007.


Calculations of global warming prepared in or before 2001 from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions.


The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. In this figure, the globally averaged warming corresponds to 3.0 °C (5.4 °F).
Main article: Global climate model
Scientists have studied global warming with computer models of the climate. These models are based on physical principles of fluid dynamics, radiative transfer, and other processes, with some simplifications being necessary because of limitations in computer power. These models predict that the net effect of adding greenhouse gases is to produce a warmer climate. However, even when the same assumptions of fossil fuel consumption and CO2 emission are used, the amount of projected warming varies between models and there still remains a considerable range of climate sensitivity.
Including uncertainties in future greenhouse gas concentrations and climate modelling, the IPCC anticipates a warming of 1.1 °C to 6.4 °C (2.0 °F to 11.5 °F) between 1990 and 2100.[1] Models have also been used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human derived causes.
Climate models can produce a good match to observations of global temperature changes over the last century, but cannot yet simulate all aspects of climate.[37] These models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects; however, they suggest that the warming since 1975 is dominated by man-made greenhouse gas emissions.
Most global climate models, when run to project future climate, are forced by imposed greenhouse gas scenarios, generally one from the IPCC Special Report on Emissions Scenarios (SRES). Less commonly, models may be run by adding a simulation of the carbon cycle; this generally shows a positive feedback, though this response is uncertain (under the A2 SRES scenario, responses vary between an extra 20 and 200 ppm of CO2). Some observational studies also show a positive feedback.[38][39][40]
The representation of clouds is one of the main sources of uncertainty in present-generation models, though progress is being made on this problem.[41] There is also an ongoing discussion as to whether climate models are neglecting important indirect and feedback effects of solar variability.
Attributed and expected effects
Main article: Effects of global warming


Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to the WGMS and the NSIDC.
Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, increased intensity and frequency of extreme weather events, are being attributed in part to global warming.[42] While changes are expected for overall patterns, intensity, and frequencies, it is difficult to attribute specific events to global warming. Other expected effects include water scarcity in some regions and increased precipitation in others, changes in mountain snowpack, adverse health effects from warmer temperatures.
Increasing deaths, displacements, and economic losses projected due to extreme weather attributed to global warming may be exacerbated by growing population densities in affected areas, although temperate regions are projected to experience some minor benefits, such as fewer deaths due to cold exposure.[43] A summary of probable effects and recent understanding can be found in the report made for the IPCC Third Assessment Report by Working Group II.[42] The newer IPCC Fourth Assessment Report summary reports that there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since about 1970, in correlation with the increase in sea surface temperature, but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations. The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.[1]
Additional anticipated effects include sea level rise of 110 to 770 millimeters (0.36 to 2.5 ft) between 1990 and 2100,[44] repercussions to agriculture, possible slowing of the thermohaline circulation, reductions in the ozone layer, increased intensity and frequency of hurricanes and extreme weather events, lowering of ocean pH, and the spread of diseases such as malaria and dengue fever. One study predicts 18% to 35% of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections.[45] Two populations of Bay checkerspot butterfly are being threatened by changes in precipitation, though few mechanistic studies have documented extinctions due to recent climate change.[46]
Economics
Main article: Economics of global warming
Some economists have tried to estimate the aggregate net economic costs of damages from climate change across the globe. Such estimates have so far failed to reach conclusive findings; in a survey of 100 estimates, the values ran from US$-10 per tonne of carbon (tC) (US$-3 per tonne of carbon dioxide) up to US$350/tC (US$95 per tonne of carbon dioxide), with a mean of US$43 per tonne of carbon (US$12 per tonne of carbon dioxide).[43] One widely-publicized report on potential economic impact is the Stern Review; it suggests that extreme weather might reduce global gross domestic product by up to 1%, and that in a worst case scenario global per capita consumption could fall 20%.[47] The report's methodology, advocacy and conclusions has been criticized by many economists, primarily around the Review's assumptions of discounting and its choices of scenarios.[48] , while others have supported the general attempt to quantify economic risk, even if not the specific numbers[49] [50].
In a summary of economic cost associated with climate change, the United Nations Environment Programme emphasizes the risks to insurers, reinsurers, and banks of increasingly traumatic and costly weather events. Other economic sectors likely to face difficulties related to climate change include agriculture and transport. Developing countries, rather than the developed world, are at greatest economic risk.[51]
Mitigation and adaptation
Main articles: Mitigation of global warming, adaptation to global warming, and Kyoto Protocol
The broad agreement among climate scientists that global temperatures will continue to increase has led nations, states, corporations and individuals to implement actions to try to curtail global warming or adjust to it. Many environmental groups encourage action against global warming, often by the consumer, but also by community and regional organizations. There has been business action on climate change, including efforts at increased energy efficiency and (still limited) moves to alternative fuels. One important innovation has been the development of greenhouse gas emissions trading through which companies, in conjunction with government, agree to cap their emissions or to purchase credits from those below their allowances.
The world's primary international agreement on combating global warming is the Kyoto Protocol, an amendment to the United Nations Framework Convention on Climate Change (UNFCCC), negotiated in 1997. The Protocol now covers more than 160 countries globally and over 55% of global greenhouse gas emissions.[52] The United States (historically the world's largest greenhouse gas emitter), Australia, and Kazakhstan have not ratified the treaty. China and India, two other large emitters, have ratified the treaty but, as developing countries, are exempt from its provisions. This treaty expires in 2012, and international talks began in May 2007 on a future treaty to succeed the current one.[53]
The world's primary body for crafting a response is the Intergovernmental Panel on Climate Change (IPCC), a UN-sponsored activity which holds periodic meetings between national delegations on the problems of global warming, and issues working papers and assessments on the current status of the science of climate change, impacts, and mitigation. It convenes four different working groups examining various specific issues. For example, in May 2007, the IPCC held conferences in Bonn, Germany,[54] and in Bangkok, Thailand.[55]
Issue debate and political processes
Main articles: Global warming controversy and politics of global warming
Increased awareness of the scientific findings surrounding global warming has resulted in political and economic debate. Poor regions, particularly Africa, appear at greatest risk from the suggested effects of global warming, while their actual emissions have been negligible compared to the developed world[56]. At the same time, developing country exemptions from provisions of the Kyoto Protocol have been criticized by the United States and been used as part of its justification for continued non-ratification.[57] In the Western world, the idea of human influence on climate and efforts to combat it has gained wider acceptance in Europe than in the United States.[58][59]
Fossil fuel companies such as ExxonMobil and some think tanks such as the Competitive Enterprise Institute and the Cato Institute have campaigned to downplay the risks of climate change,[60][61] while environmental groups have launched campaigns emphasizing the risks. Recently, some fossil fuel companies have scaled back such efforts[62] or called for policies to reduce global warming.[63]
This issue has sparked debate in the U.S. about the benefits of limiting industrial emissions of greenhouse gases to reduce impacts to the climate, versus the effects on economic activity.[64][65] There has also been discussion in several countries about the cost of adopting alternate, cleaner energy sources in order to reduce emissions.[66]
Another point of debate is the degree to which newly-developed economies, like India and China, should be expected to constrain their emissions. China's CO2 emissions are expected to exceed those of the U.S. within the next few years (and according to one report may have already done so[67]).
Related climatic issues
Main articles: Ocean acidification, global dimming, and ozone depletion
A variety of issues are often raised in relation to global warming. One is ocean acidification. Increased atmospheric CO2 increases the amount of CO2 dissolved in the oceans.[68] CO2 dissolved in the ocean reacts with water to form carbonic acid resulting in acidification. Ocean surface pH is estimated to have decreased from approximately 8.25 to 8.14 since the beginning of the industrial era,[69] and it is estimated that it will drop by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO2.[1][70] Since organisms and ecosystems are adapted to a narrow range of pH, this raises extinction concerns, directly driven by increased atmospheric CO2, that could disrupt food webs and impact human societies that depend on marine ecosystem services.[71]
Another related issue that may have partially mitigated global warming in the late twentieth century is global dimming, the gradual reduction in the amount of global direct irradiance at the Earth's surface. From 1960 to 1990 human-caused aerosols likely precipitated this effect. Scientists have stated with 66–90% confidence that the effects of human-caused aerosols, along with volcanic activity, have offset some of global warming, and that greenhouse gases would have resulted in more warming than observed if not for these dimming agents.[1]
Ozone depletion, the steady decline in the total amount of ozone in Earth's stratosphere, is frequently cited in relation to global warming. Although there are areas of linkage, the relationship between the two is not strong.
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Further reading
· Amstrup, Steven C.; Ian Stirling, Tom S. Smith, Craig Perham, Gregory W. Thiemann (2006-04-27). "Recent observations of intraspecific predation and cannibalism among polar bears in the southern Beaufort Sea". Polar Biology 29 (11): 997–1002. DOI:10.1007/s00300-006-0142-5.
· Association of British Insurers (2005-06). Financial Risks of Climate Change (PDF).
· Barnett, Tim P.; J. C. Adam, D. P. Lettenmaier (2005-11-17). "Potential impacts of a warming climate on water availability in snow-dominated regions". Nature 438 (7066): 303–309. DOI:10.1038/nature04141.
· Behrenfeld, Michael J.; Robert T. O'Malley, David A. Siegel, Charles R. McClain, Jorge L. Sarmiento, Gene C. Feldman, Allen G. Milligan, Paul G. Falkowski, Ricardo M. Letelier, Emanuel S. Boss (2006-12-07). "Climate-driven trends in contemporary ocean productivity" (PDF). Nature 444 (7120): 752–755. DOI:10.1038/nature05317.
· Choi, Onelack; Ann Fisher (May 2005). "The Impacts of Socioeconomic Development and Climate Change on Severe Weather Catastrophe Losses: Mid-Atlantic Region (MAR) and the U.S.". Climate Change 58 (1–2): 149–170. DOI:10.1023/A:1023459216609.
· Dyurgerov, Mark B.; Mark F. Meier (2005). Glaciers and the Changing Earth System: a 2004 Snapshot (PDF), Institute of Arctic and Alpine Research Occasional Paper #58. ISSN 0069-6145.
· Emanuel, Kerry A. (2005-08-04). "Increasing destructiveness of tropical cyclones over the past 30 years." (PDF). Nature 436 (7051): 686–688. DOI:10.1038/nature03906.
· Hansen, James; Larissa Nazarenko, Reto Ruedy, Makiko Sato, Josh Willis, Anthony Del Genio, Dorothy Koch, Andrew Lacis, Ken Lo, Surabi Menon, Tica Novakov, Judith Perlwitz, Gary Russell, Gavin A. Schmidt, Nicholas Tausnev (2005-06-03). "Earth's Energy Imbalance: Confirmation and Implications" (PDF). Science 308 (5727): 1431–1435. DOI:10.1126/science.1110252.
· Hinrichs, Kai-Uwe; Laura R. Hmelo, Sean P. Sylva (2003-02-21). "Molecular Fossil Record of Elevated Methane Levels in Late Pleistocene Coastal Waters". Science 299 (5610): 1214–1217. DOI:10.1126/science.1079601.
· Hirsch, Tim. "Plants revealed as methane source", BBC, 2006-01-11.
· Hoyt, Douglas V.; Kenneth H. Schatten (1993–11). "A discussion of plausible solar irradiance variations, 1700–1992". Journal of Geophysical Research 98 (A11): 18,895–18,906.
· Kenneth, James P.; Kevin G. Cannariato, Ingrid L. Hendy, Richard J. Behl (2003-02-14). Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. American Geophysical Union.
· Keppler, Frank, Marc Brass, Jack Hamilton, Thomas Röckmann. "Global Warming - The Blame Is not with the Plants", Max Planck Society, 2006-01-18.
· Kurzweil, Raymond (2006–07). "Nanotech Could Give Global Warming a Big Chill" (PDF). Forbes / Wolfe Nanotech Report 5 (7).
· Lean, Judith L.; Y.M. Wang, N.R. Sheeley (2002–12). "The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate". Geophysical Research Letters 29 (24). DOI:10.1029/2002GL015880.
· Lerner, K. Lee; Brenda Wilmoth Lerner (2006-07-26). Environmental issues : essential primary sources.. Thomson Gale. ISBN 1414406258.
· McLaughlin, Joseph B.; Angelo DePaola, Cheryl A. Bopp, Karen A. Martinek, Nancy P. Napolilli, Christine G. Allison, Shelley L. Murray, Eric C. Thompson, Michele M. Bird, John P. Middaugh (2005-10-06). "Outbreak of Vibrio parahaemolyticus gastroenteritis associated with Alaskan oysters". New England Journal of Medicine 353 (14): 1463–1470. (online version requires registration)
· Muscheler, Raimund; Fortunat Joos, Simon A. Müller, Ian Snowball (2005-07-28). "Climate: How unusual is today's solar activity?" (PDF). Nature 436 (7012): 1084–1087. DOI:10.1038/nature04045.
· Oerlemans, J. (2005-04-29). "Extracting a Climate Signal from 169 Glacier Records" (PDF). Science 308 (5722): 675–677. DOI:10.1126/science.1107046.
· Oreskes, Naomi (2004-12-03). "Beyond the Ivory Tower: The Scientific Consensus on Climate Change" (PDF). Science 306 (5702): 1686. DOI:10.1126/science.1103618.
· Purse, Bethan V.; Philip S. Mellor, David J. Rogers, Alan R. Samuel, Peter P. C. Mertens, Matthew Baylis (February 2005). "Climate change and the recent emergence of bluetongue in Europe". Nature Reviews Microbiology 3 (2): 171–181. DOI:10.1038/nrmicro1090.
· Revkin, Andrew C. "Rise in Gases Unmatched by a History in Ancient Ice", The New York Times, 2005-11-05.
· Ruddiman, William F. (2005-12-15). Earth's Climate Past and Future. New York: Princeton University Press. ISBN 0-7167-3741-8.
· Ruddiman, William F. (2005-08-01). Plows, Plagues, and Petroleum: How Humans Took Control of Climate. New Jersey: Princeton University Press. ISBN 0-691-12164-8.
· Solanki, Sami K.; I.G. Usoskin, B. Kromer, M. Schussler, J. Beer (2004-10-23). "Unusual activity of the Sun during recent decades compared to the previous 11,000 years." (PDF). Nature 431: 1084–1087. DOI:10.1038/nature02995.
· Solanki, Sami K.; I. G. Usoskin, B. Kromer, M. Schüssler, J. Beer (2005-07-28). "Climate: How unusual is today's solar activity? (Reply)" (PDF). Nature 436: E4-E5. DOI:10.1038/nature04046.
· Sowers, Todd (2006-02-10). "Late Quaternary Atmospheric CH4 Isotope Record Suggests Marine Clathrates Are Stable". Science 311 (5762): 838–840. DOI:10.1126/science.1121235.
· Svensmark, Henrik; Jens Olaf P. Pedersen, Nigel D. Marsh, Martin B. Enghoff, Ulrik I. Uuggerhøj (2007-02-08). "Experimental evidence for the role of ions in particle nucleation under atmospheric conditions". Proceedings of the Royal Society A 463 (2078): 385–396. DOI:10.1098/rspa.2006.1773. (online version requires registration)
· Walter, K. M.; S. A. Zimov, Jeff P. Chanton, D. Verbyla, F. S. Chapin (2006-09-07). "Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming". Nature 443 (7107): 71–75. DOI:10.1038/nature05040.
· Wang, Y.-M.; J.L. Lean, N.R. Sheeley (2005-05-20). "Modeling the sun's magnetic field and irradiance since 1713" (PDF). Astrophysical Journal 625: 522–538. DOI:10.1086/429689.
External links
Scientific
· Intergovernmental Panel on Climate Change (IPCC)
· Nature Reports Climate Change
· NOAA's Global Warming FAQ
· Outgoing Longwave Radiation pentad mean - NOAA Climate Prediction Center
· Discovery of Global Warming — An extensive introduction to the topic and the history of its discovery
· Caution urged on climate 'risks'
· NASA Finds Sun-Climate Connection in Old Nile Records
· News in Science - Night flights are worse for global warming - 15/06/2006
Educational
· What Is Global Warming? Simulation from National Geographic
· The EdGCM (Educational Global Climate Modelling) Project free research-quality simulation for students, educators, and scientists alike, with a user-friendly interface that runs on desktop computers
· Daily global temperatures and trends from satellites Interactive graphics from NASA
· The Pew Center on global climate change
Other
· The Global Warming Survival Guide from Time.com
· UBS Launches First Global Warming Index "UBS-GWI"
· Global Warming News & Articles Portal
· UN: rearing cattle produces more greenhouse gases than driving cars
· Science and Technology Librarianship: Global Warming and Climate Change Science – Extensive commented list of Internet resources – Science and Technology Sources on the Internet.
· Union of Concerned Scientists Global Warming page
· Watch and read 'Tipping Point', Australian science documentary about effects of global warming on rare, common, and endangered wildlife
· Newest reports on U.S. EPA website
· IPS Inter Press Service — Independent news on global warming and its consequences.
· Indonesia Counts Its Islands Before It Is Too Late
· World Environment Day 2007 "Melting Ice" image gallery at The Guardian
· Climate Counts - corporate watchdog
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Global warming and Climate change (Category:Global warming and Category:Climate change)
Temperatures
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Causes
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Greenhouse Gases • Global warming potential • Greenhouse effect • Carbon dioxide • Keeling Curve • Climate sensitivitySolar variation • Radiative forcing • Global dimming • Global cooling
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Issues
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Politics
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Effects
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Mitigation
Kyoto Protocol • Emissions trading • Carbon tax • Clean Development Mechanism • Carbon dioxide sink (Carbon sequestration) • Energy conservationRenewable energy • Renewable energy development • Soft energy path
Adaptation
United Kingdom Climate Change Programme • European Climate Change Programme
Retrieved from "http://en.wikipedia.org/wiki/Global_warming"
Categories: Semi-protected | Climate change | Climate change feedbacks and causes | History of climate | Global warming | Economic problems
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