为什么巴黎气候目标还不够

: By 墨尔本大学Malte Meinshausen

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为什么巴黎的气候目标不够

巴黎气候协议 saw countries pledge to limit global warming to well below 2?, and to aim to keep it within 1.5?. The problem is that countries' current emissions targets are not enough to meet these goals.

在一个今天发表在“自然”杂志上, I and my colleagues from Austria, Brazil, China, South Africa, Germany, the Netherlands and Switzerland take a closer look at those pledges, and the studies that have so far evaluated them. The bottom line is that under the existing Paris pledges the world would be facing 2.3-3.5? of warming by 2100.

承诺，被称为国家自主贡献或“国家自主贡献”将导致排放14数十亿吨，高于2030应该以最便宜的途径限制变暖。

While this path is well below the “business as usual” scenario, it is not yet in the range of the 1.5-2? objectives we have set ourselves. So it’s a first step, but bigger steps are needed.

我们在2030之前所做的努力越少，之后的减排就越困难。不过，我和我的同事发现，有几种方法可以缩小差距。

为什么目标在 2030 年后变得更加困难？

To limit global warming to any level, we ultimately have to completely stop CO? emissions and ramp down other greenhouse gas emissions. For any given warming threshold, we have to limit total emissions to a certain amount, known as the “carbon budget”.

It is likely that to keep warming well below 2? we have a remaining carbon budget of between 750 billion and 1.2 trillion tonnes. For context, global emissions in 2010 were around 50 billion tonnes.

Remaining on the current path, as laid out by the INDCs, would mean the world would have to make very drastic cuts in emissions after 2030 to keep warming below 2? (and would likely make the 1.5? limit completely unachievable).

这个大幅度的削减将意味着大量的搁浅投资，因为排放量将持续上升到2030，这意味着对基础设施的持续投资将无法实现我们的长期目标。对于“过渡”燃料（如天然气）的投资也是如此。如果目前的投资不能成为接近零排放的2050世界的一部分，那么他们可能不得不在通常的使用日期之前退休。

如果在2030中突然意识到我们必须做更多的事，世界将不得不每年减少3-4％。像澳大利亚这样的国家每年都要削减10％。这就像慢慢地走到悬崖边，然后跳下去。

This is not the cheapest way to keep warming below 2?. The least-cost option is to start investing now in the right technology. The 国际能源署认为如果我们要在2050中实现零碳经济，或者至少要有一个接近于零碳的经济，那么我们今天就需要进行零排放投资，因为需要很长时间来翻转现有的投资股票。

The other problem is carbon capture and storage (CCS). The Paris Agreement pledges net zero greenhouse gas emissions after 2050. There is no pathway to this that doesn’t involve “net-negative” emissions, because there will still be some greenhouse gas emissions we can’t reduce, and we will have already overshot the carbon budget for keeping warming below 2?, let alone 1.5?. So we are going to have to come up with a way to pull CO? from the atmosphere.

How can we do that? The main option is thought to be bio-energy with carbon capture and storage (BECCS). This process involves growing biomass fuel, such as trees, then using the woodchips to produce electricity, then capturing the CO? produced, and finally sequestering and storing it underground.

过去，CCS主要与化石燃料结合在一起。但风能和太阳能成本的大幅下降将使电力部门的脱碳更容易。

CCS would also likely require a carbon price, to incentivise the necessary investment in CCS by 2030. Retrofitting existing fossil fuel power plants with CCS or keeping coal demand high by supporting new coal power plants with CCS in India and China is hence likely an uphill battle that is lost on economic grounds. However, we would still need CCS and specifically BECCS to remove CO? from the atmosphere.