刊登在英國《自然—氣候變化》周刊上的兩份研究報告警告，如果溫室氣體排放量繼續(xù)增加,，那么在我們很多人的有生之年，全球氣溫升幅在世界上部分地區(qū)將超過2攝氏度這一“安全”值,。
英國雷丁大學,、英國牛津大學、英國氣象局哈德利氣候預測與研究中心,、新西蘭惠靈頓維多利亞大學的學者發(fā)表的一份研究報告中說：“在目前世界上很多人的有生之年,，很可能會出現某種程度的氣候變化……除非溫室氣體的排放量在今后幾十年內大幅減少。”
這份報告說：“到2030年,，歐亞,、北非、加拿大的大片地區(qū)很可能會經歷一個平均氣溫升幅超過2攝氏度閥值的五年期,。這個時標并非那么遙遠,。”
兩年前，工業(yè)化國家將氣溫上升2攝氏度定為避免洪澇,、干旱,、海平面上升等危險氣候變化的最大限值，而一些專家則認為1.5攝氏度的限值可能更安全一些,。
科學家普遍認為,，迄今為止全球限制溫室氣體排放量的承諾還不足以阻止“危險”的氣候變化。
下個月,，世界各國將在南非德班召開下一屆聯合國氣候大會,，但會議似乎不大可能通過一項削減溫室氣體排放量的有約束力的協議,。
事實上，在2014年至2015年之前可能都不會出現這樣一份全球協議,。
此次研究發(fā)現,，到2060年，世界上大部分陸地很可能都會經歷一個平均氣溫比工業(yè)化時代以前高出2攝氏度的五年期,。
報告還說,，假如大幅減少溫室氣體排放量，達到2攝氏度閥值的時間可能最多會被推遲數十年,。
不過,，即使全球氣溫升幅因為溫室氣體排放量大幅減少而被控制在2攝氏度之內，部分地區(qū)仍然無法避免變暖,，而且,，即使是在一個略微變暖的世界里，出現熱浪等極端天氣事件的可能性也仍然很大,。
瑞士蘇黎世大氣及氣象學研究所,、德國波茨坦氣候影響研究所、英國氣象局哈德利氣候預測與研究中心等機構的學者在另一份研究報告中指出,，將氣溫升幅控制在2攝氏度之內將是一項挑戰(zhàn),。
要想把氣溫升幅控制在2攝氏度以內的可能性維持在66%以上，那么全球溫室氣體排放量很可能需要在2020年之前就見頂回落,，并在2020年使二氧化碳排放量減少至大約440億噸,。
這份研究報告說：“如果不能堅決承諾落實減排機制，使全球溫室氣體排放量提前見頂回落,，那么很多國家所認同的2攝氏度閥值將很可能被逐漸超越,。”（生物谷 Bioon.com)
doi:10.1038/nclimate1261
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Projections of when temperature change will exceed 2 °C above pre-industrial levels
Manoj Joshi,1 Ed Hawkins,1 Rowan Sutton,1 Jason Lowe2 & David Frame3, 4
Climate change projections are usually presented as 'snapshots' of change at a particular time in the future. Instead, we consider the key question 'when will specific temperature thresholds be exceeded?' Framing the question as 'when might something happen (either permanently or temporarily)?' rather than 'what might happen?' demonstrates that lowering future emissions will delay the crossing of temperature thresholds and buy valuable time for planning adaptation. For example, in higher greenhouse-gas emission scenarios, a global average 2 °C warming threshold is likely to be crossed by 2060, whereas in a lower emissions scenario, the crossing of this threshold is delayed by up to several decades. On regional scales, however, the 2 °C threshold will probably be exceeded over large parts of Eurasia, North Africa and Canada by 2040 if emissions continue to increase — well within the lifetime of many people living now.
doi:10.1038/nclimate1258
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Emission pathways consistent with a 2 °C global temperature limit
Joeri Rogelj,1 William Hare,2, 3 Jason Lowe,4 Detlef P. van Vuuren,5, 6 Keywan Riahi,7 Ben Matthews,8 Tatsuya Hanaoka,9 Kejun Jiang10 & Malte Meinshausen2, 11
In recent years, international climate policy has increasingly focused on limiting temperature rise, as opposed to achieving greenhouse-gas-concentration-related objectives. The agreements reached at the United Nations Framework Convention on Climate Change conference in Cancun in 2010 recognize that countries should take urgent action to limit the increase in global average temperature to less than 2 °C relative to pre-industrial levels1. If this is to be achieved, policymakers need robust information about the amounts of future greenhouse-gas emissions that are consistent with such temperature limits. This, in turn, requires an understanding of both the technical and economic implications of reducing emissions and the processes that link emissions to temperature. Here we consider both of these aspects by reanalysing a large set of published emission scenarios from integrated assessment models in a risk-based climate modelling framework. We find that in the set of scenarios with a ‘likely’ (greater than 66%) chance of staying below 2 °C, emissions peak between 2010 and 2020 and fall to a median level of 44 Gt of CO2 equivalent in 2020 (compared with estimated median emissions across the scenario set of 48 Gt of CO2 equivalent in 2010). Our analysis confirms that if the mechanisms needed to enable an early peak in global emissions followed by steep reductions are not put in place, there is a significant risk that the 2 °C target will not be achieved.
