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Human actions—primarily burning fossil fuels, but also deforestation and other activities—have resulted in a rapid increase in the concentration of GHGs in the atmosphere. GHGs, including carbon dioxide, methane, and nitrous oxide, trap heat close to the surface and cause global temperatures to rise. Since the industrial revolution, CO2 concentrations have risen by more than 30%—currently 420 parts per million, up from 180 to 300 ppm historically over the prior several hundred million years. The result has been an average global temperature increase of approximately 0.2°C per decade. Today, mean surface temperatures are approximately 1.2°C (2.1°F) warmer than in the preindustrial period—enough to destabilize large ecosystems around the globe.
人類燃燒化石燃料以及砍伐森林等行為，導(dǎo)致大氣中溫室氣體濃度快速升高。二氧化碳、甲烷和氧化亞氮等溫室氣體將熱量俘獲，并儲(chǔ)存在地表，導(dǎo)致全球氣溫升高。自工業(yè)革命以來，二氧化碳濃度提高了超過30%，目前已經(jīng)達(dá)到420 ppm（百萬分率），而在歷史上，二氧化碳濃度從180 ppm提升到300 ppm，用了數(shù)億年時(shí)間。二氧化碳濃度提高導(dǎo)致全球氣溫平均每十年升高約0.2攝氏度。目前的平均地表溫度較前工業(yè)化時(shí)期提高了約1.2攝氏度（2.1華氏度），足以在全世界造成大規(guī)模的生態(tài)系統(tǒng)動(dòng)蕩。
Scientists’ climate models have thus far been remarkably accurate at predicting global temperature rise. And forecasts have generally underestimated the speed and severity of the impacts of a changing climate—for example, glaciers and ice sheets—are melting far more quickly than most climate scientists expected even just five years ago. Today, many scientists see a range of once- unlikely climate tipping points—including the rapid collapse of ice sheets, thawing permafrost in the Arctic, and the disruption of critical ocean currents—as “too risky to bet against.” Any one of these (factors/tipping points/possibilities) is potentially cataclysmic in its impact, and is a plausible outcome within our lifetimes.
到目前為止，科學(xué)家們的氣候模型都非常精確地預(yù)測(cè)了全球氣溫升高的結(jié)果，但預(yù)測(cè)結(jié)果普遍低估了氣候變化的速度及其對(duì)生態(tài)影響的嚴(yán)重程度。例如，冰山和冰蓋的融化速度甚至遠(yuǎn)遠(yuǎn)超過了大多數(shù)氣候科學(xué)家五年前的預(yù)期。今天，許多科學(xué)家認(rèn)為以前不太可能出現(xiàn)的各類氣候臨界點(diǎn)，例如冰蓋快速崩解、北極永凍層解凍和關(guān)鍵洋流中斷等都有出現(xiàn)的可能，因此我們“面臨的風(fēng)險(xiǎn)太大，不可存有僥幸心理”。任何一種因素/臨界點(diǎn)/可能性都會(huì)產(chǎn)生災(zāi)難性的影響，而且在我們有生之年似乎就能成為現(xiàn)實(shí)。