碳邊境調節稅不具備可行性

When Donald Trump announced last week that the US was pulling out of the Paris accord on climate change, other governments were rightly determined that the move neither derail the drive for lower carbon emissions nor allow the US to gain a competitive advantage.

不久前當唐納德?特朗普(Donald Trump)宣佈美國將退出巴黎氣候變化協定時，其他國家政府明智地認定，此舉既破壞不了全球推動減少碳排放量的努力，也不會讓美國因此獲得競爭性優勢。

Thoughts immediately turned to carbon border tax adjustments, a way of instituting a single international price of carbon by penalising the exports of countries with no domestic emissions pricing of their own. Like the best climate change policies, it is an elegant idea, tweaking a price and allowing the free market to respond rather than attempting a complex series of direct interventions.

各國政府的想法立即轉向碳邊境調節稅——制定統一的國際碳稅標準，對那些在本國沒有徵收碳稅的國家的出口商品施加懲罰。正如最好的氣候變化政策一樣，這是個絕妙的想法——調整價格並允許自由市場做出應對，而不是試圖進行一系列複雜的直接干預。

However, like many good ideas, the reality is far more complex. Fiendish calculations requiring detailed data, together with potential legal impediments, unfortunately suggest a more piecemeal approach might yield better returns.

然而，像很多好點子一樣，現實遠比想象複雜。由於計算極爲困難，需要詳細的數據，還可能遭遇法律障礙，因此遺憾的是，更零散的策略可能帶來更好的回報。

There are various models of carbon border taxes, but the general principle is that producers in countries with carbon pricing should be protected from being undercut by those in countries without. Variations include putting an import tariff on goods from trading partners without carbon emissions measures, or those that also involve a rebate on exports, similar to the operation of value added tax.

碳邊境稅有很多不同的類型，但一般原則是徵收碳稅的國家的生產商應該受到保護，使之免受不徵收碳稅的國家的生產商的低價競爭。碳邊境稅的種類包括，對那些不採取減排措施、或同時實行出口退稅的貿易伙伴的貨物徵收關稅，與增值稅的操作類似。

However, imposing VAT, which is a percentage of a price, is straightforward. Working out a single price for carbon and delving deep into the vastly complex supply chains of a modern economy is not.

然而，徵收增值稅（按價格的一定比例徵收）是直截了當的方法。而制定統一碳稅並深入研究現代經濟異常複雜的供應鏈，則沒那麼簡單。

For a start, creating a comparable carbon cost across the varied forms of emission pricing — simple carbon tax, cap-and-trade and so forth — would be challenging. Some governments, such as Barack Obama’s administration, have sought to reduce carbon in more roundabout ways by tightening product standards, such as emissions standards for vehicles, and setting rules for power plants. All of these should clearly be taken into account, but translating them into a simple national-level price will be a highly complex and contested issue.

首先，在各式各樣的排放稅中——簡單的碳稅、“限量及交易”(cap-and-trade)機制等等——建立統一的碳稅將會是一項挑戰。一些政府（比如巴拉克?奧巴馬(Barack Obama)政府）試圖以更迂迴的方式，通過收緊產品標準（比如汽車排放標準）以及爲發電廠制定標準來減少碳排放。這些顯然應該被納入考慮，但把這些都轉化成國家層面的簡單碳稅，將是一個極爲複雜而具有爭議的問題。

More broadly, taxing all manufactured exports from, for example, the US is clearly unfair to those produced in relatively low-carbon industries, or indeed low-carbon producers within each industry. For example, for goods like cars, which source from different sectors such as glass, steel and rubber, taxing them fairly would involve disaggregating the product into the carbon emitted from each sector, and preferably each producer within each sector. Taking a broader brush approach would give a competitive advantage to the dirtier producers inside each economy by taxing them the same as cleaner companies.

更廣泛地看，比如對美國所有制造業出口產品徵收碳邊境稅，明顯對那些相對低碳的產業、或每種產業中確實更加低碳的廠商生產的產品不公平。例如，對於汽車（組件來自玻璃、鋼鐵和橡膠等不同產業）等商品來說，公平徵稅意味着，把商品按每個行業的碳排放進行拆分，最好精確到每個行業內的每家廠商。採取一刀切的辦法，對污染企業和環保企業徵收相同的稅率，會使那些污染廠商得到競爭性優勢。

A similar problem arises in disadvantaging states and cities within the US with their own carbon pricing schemes, such as California. The state-level cap-and-trade scheme is controversial there, and has led to “resource shuffling” whereby Californian producers game the system by buying stakes in out-of-state power generators, undoing the effect of carbon pricing. A blanket tariff on US exports will only worsen this problem and discourage local carbon-control initiatives.

同樣，加利福尼亞州等美國國內擁有自身碳稅方案的州和城市也被置於不利地位，這會導致問題。加州的州級“限量及交易”機制在當地引起爭議，導致企業進行“資源重組”——加州製造商通過購買州外發電廠的股份來抵消碳稅的影響，與該機制對抗。對美國出口商品統一徵收關稅，只會使該問題進一步惡化，挫傷當地碳排放控制計劃的積極性。

Finally, assuming some emerging market countries will be exempt from the system, the US will have a powerful incentive to route the sales of its goods via those countries, in effect using them as a low-carbon offshore export platform.

最後，假設某些新興市場國家將被免於徵收碳稅，美國將有強大的動力通過這些國家完成商品銷售，實際上把它們作爲境外低碳出口平臺。

A carbon border adjustment system, then, would replicate the “rules of origin” problem arising from complex supply chains with which trade practitioners are all too aware.

那麼，碳邊境調節稅將再次面臨“原產地原則”問題——該問題源於貿易參與者都非常瞭解的複雜供應鏈。

As for its legality, supporters argue that a carbon border tariff would have a good shot at passing muster at the World Trade Organization. Either it could be organised through an official plurilateral agreement (involving fewer countries than a multilateral agreement) or it could invoke a WTO law allowing import restrictions to protect exhaustible natural resources.

至於碳邊境稅的合法性，支持者認爲碳邊境稅很可能在世界貿易組織(WTO)獲得通過。要麼它可以通過官方諸邊協議（涉及的國家少於多邊協議）實現，要麼可以促使WTO立法允許爲保護過度消耗的自然資源採取進口限制。

But given the suspicion in which Mr Trump’s administration holds the WTO, a favourable ruling from its judicial panel is only likely to increase his willingness to ignore or leave the organisation altogether.

但鑑於特朗普政府控制着WTO的這種猜測，WTO專家小組的有利裁決只可能增強他忽視或徹底退出WTO的意願。

Carbon border adjustments are theoretically elegant. But the technical complexities involved unfortunately suggest other solutions might be more constructive, including trying to encourage more states and cities inside the US to band together and impose their own carbon regimes from the bottom up, or trying to institute international low-carbon product standards for goods such as vehicles.

理論上，碳邊境調節稅是絕妙的想法。但遺憾的是，其中涉及的技術層面的複雜性意味着其他解決方案可能更有建設性，其中包括嘗試鼓勵美國更多州和市團結在一起、自上而下地推行各地的碳機制，或嘗試爲汽車等商品制定國際低碳產品標準。

There is a heartening amount of political will from the major economies to press ahead with carbon emissions reduction in the face of Mr Trump’s destructive decision. But the technical challenges of designing an international carbon border tax may be even harder than summoning the political will to create it.

令人振奮的是，面對特朗普破壞性的決定，主要經濟體推進碳減排措施的政治意願非常強烈。但制定國際碳邊境調節稅在技術層面上的挑戰，可能比聚集各國制定該機制的政治意願更難。

The writer is an FT leader writer

本文作者爲英國《金融時報》的社評撰稿人