刊登在英国《自然—气候变化》周刊上的两份研究报告警告，如果温室气体排放量继续增加，那么在我们很多人的有生之年，全球气温升幅在世界上部分地区将超过2摄氏度这一“安全”值。
英国雷丁大学、英国牛津大学、英国气象局哈德利气候预测与研究中心、新西兰惠灵顿维多利亚大学的学者发表的一份研究报告中说：“在目前世界上很多人的有生之年，很可能会出现某种程度的气候变化……除非温室气体的排放量在今后几十年内大幅减少。”
这份报告说：“到2030年，欧亚、北非、加拿大的大片地区很可能会经历一个平均气温升幅超过2摄氏度阀值的五年期。这个时标并非那么遥远。”
两年前，工业化国家将气温上升2摄氏度定为避免洪涝、干旱、海平面上升等危险气候变化的最大限值，而一些专家则认为1.5摄氏度的限值可能更安全一些。
科学家普遍认为，迄今为止全球限制温室气体排放量的承诺还不足以阻止“危险”的气候变化。
下个月，世界各国将在南非德班召开下一届联合国气候大会，但会议似乎不大可能通过一项削减温室气体排放量的有约束力的协议。
事实上，在2014年至2015年之前可能都不会出现这样一份全球协议。
此次研究发现，到2060年，世界上大部分陆地很可能都会经历一个平均气温比工业化时代以前高出2摄氏度的五年期。
报告还说，假如大幅减少温室气体排放量，达到2摄氏度阀值的时间可能最多会被推迟数十年。
不过，即使全球气温升幅因为温室气体排放量大幅减少而被控制在2摄氏度之内，部分地区仍然无法避免变暖，而且，即使是在一个略微变暖的世界里，出现热浪等极端天气事件的可能性也仍然很大。
瑞士苏黎世大气及气象学研究所、德国波茨坦气候影响研究所、英国气象局哈德利气候预测与研究中心等机构的学者在另一份研究报告中指出，将气温升幅控制在2摄氏度之内将是一项挑战。
要想把气温升幅控制在2摄氏度以内的可能性维持在66%以上，那么全球温室气体排放量很可能需要在2020年之前就见顶回落，并在2020年使二氧化碳排放量减少至大约440亿吨。
这份研究报告说：“如果不能坚决承诺落实减排机制，使全球温室气体排放量提前见顶回落，那么很多国家所认同的2摄氏度阀值将很可能被逐渐超越。”（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.
