政府间气候变化专门委员会1.5?报告:气候科学是这么说的

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世界气候科学家纷纷发声:如果我们想将人类引起的全球变暖限制在1.5以内?我们也许可以。但考虑到我们的起点,这将是艰难的。

这是一个结论 新报告 by the UN’s Intergovernmental Panel on Climate Change (IPCC). The focus on 1.5? is the result of years of international negotiation. Starting in 1994, a central aim of the UN’s climate change efforts (the Framework Convention on Climate Change, or UNFCCC) was to stabilise greenhouse gas concentrations at a level that would “prevent dangerous anthropogenic interference with the climate system”. Much was written on what this meant, particularly the word “dangerous”.

气候变化的负面影响是连续的,并且定义气候变化变得危险的点是困难和有争议的。 另一方面,如果没有一些目标努力,气候变化谈判就很困难。

Fifteen years later, the UNFCCC’s Copenhagen Accord introduced a 2? target, and its 2015 巴黎协定 was even more specific: it “aims to strengthen the global response to the threat of climate change … by holding the increase in … temperature to well below 2? above pre-industrial levels and pursuing efforts to limit the … increase to 1.5?”.

IPCC向制定政策的UNFCCC提供科学建议,而IPCC本身从未说过温度目标。 然而,它确实列出了五个“关注原因”的气候变化风险。 其中包括“独特和受威胁的生态系统和文化”(如珊瑚礁)和“极端天气事件”等影响,每个影响的评级从“不可检测”到“非常高”。 IPCC最新(2014) 第五次评估 of the scientific evidence found that at around 1.5? warming there was a transition 从中度到高度的风险 受威胁的生态系统和文化以及极端天气事件。 因此,巴黎和IPCC评估之间存在一致性。


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政府间气候变化专门委员会1.5?报告:气候科学是这么说的气候变化将使某些类型的极端天气更加普遍。 德鲁麦克阿瑟/ Shutterstock

The Paris Agreement asked the IPCC to report on the impacts of global warming of 1.5?, and this new publication is the result. Its tone is not “we must avoid 1.5? warming”, as you might think from many commentators, but more “if we want to avoid 1.5? warming, this is what must be done”. The report contrasts the impact of 1.5? and 2? warmings, giving information on what would be gained by the extra effort needed to limit warming to 1.5?.

As the IPCC’s reports are largely based on a critical assessment and synthesis of published scientific papers, many of its latest conclusions are unsurprising. There are many well recognised uncertainties in understanding climate change - for instance, even if we set a course aiming to hit 1.5? (which is mostly determined by future CO? emissions), we could end up hitting, say, 1? or 2? instead. The report provides uncertainty ranges in its estimates and confidence levels, based on expert judgement.

The new report tells us that human activity has already caused about 1? of global warming, while at the present rate of warming (0.2? per decade) we’ll hit 1.5? by about 2040. National pledges made as part of the Paris Agreement still mean we are on course for warming of about 3? by 2100, meaning four of the five “reasons for concern” would then be in the high to very-high risk category.

Achieving the 1.5? target will require anthropogenic CO? emissions to decline by 45% by 2030 (relative to 2010). By 2050, they will need to reach “net zero” - any further CO? emissions due to human activity would then have to be matched by 故意删除 of CO? already in the atmosphere, including by planting trees. Net zero would have to occur by around 2075 to meet a 2? target.

政府间气候变化专门委员会1.5?报告:气候科学是这么说的 泰国的再造林项目。 Somrerk Witthayanantw / Shutterstock

Many illustrations are given for the difference between 1.5? and 2? worlds. At 1.5?, summertime Arctic sea ice is projected to disappear once per century, compared to once per decade at 2?; 8% of plants that have been studied would lose half their climatically-suitable area, compared to 16%; sea level rise would be 10cm less (with 10m fewer people impacted at today’s population levels); and while coral reefs might decline by a further 80% at 1.5?, they could virtually disappear at 2?.

The report identifies various routes by which emissions cuts would limit warming to 1.5?; each makes assumptions about future changes in, for example, economic strategy, population growth and the rate at which low carbon energy is adopted. The IPCC recognises the challenges are “unprecedented in scale” but notes, for example, “the feasibility of solar energy, wind energy and electricity storage mechanisms have substantially improved over the past few years”.

The report is sensitive to the fact that changes required to meet 1.5? must be consistent with the UN’s wider 可持续发展目标。 限制气候变化将有助于实现与健康,清洁能源,城市和海洋相关的目标。 但是,“如果不加以谨慎管理”,对其他人(贫困,饥饿,水,能源获取)可能产生负面影响。

那么接下来呢? 当然,这些结论将在很多层面上进行广泛的辩论,但在12月初在波兰卡托维兹举行的下一次会议上,将关注联合国气候变化框架公约的回应。谈话

关于作者

Keith Shine,Regius气象学和气候科学教授, 雷丁大学

本文重新发表 谈话 根据知识共享许可。 阅读 原创文章.

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