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The social cost of carbon is notional, if sometimes consequential.
碳排放的社會成本是名義上的，盡管有時會產生重大影響。
The costs charged in carbon-pricing schemes are real.
碳定價方案的成本是真實存在的。
Such systems typically place a cap on emissions from a certain sector, and then distribute (often by auction) permits to emit that are equal to that cap.
這類制度通常會對某一行業(yè)設定排放上限，然后分配(通常通過拍賣)與該上限相等的排放許可。
Firms then trade permits in a “compliance market”.
然后，企業(yè)在“合規(guī)市場”上交易許可證。
Economists like these market-based “cap and trade” schemes because they discover the firms most willing to make cuts.
經濟學家喜歡這些以市場為基礎的“總量控制與交易”計劃，因為它們發(fā)掘了最愿意減排的企業(yè)。
That spreads the burden in an efficient way and lowers the total cost of keeping emissions below the cap.
這以一種有效的方式分散了負擔，降低了將排放控制在上限以下的總成本。
But even when efficiently spread, the total cost is something which most of the governments experimenting with such schemes have wanted to keep low: the average price charged in the world’s emissions-trading systems is about $20.
但是，即使能有效地分散成本，大多數(shù)試驗此類計劃的政府也想要將總成本保持在較低水平:世界排放交易系統(tǒng)的平均價格約為20美元。
The imf estimates that for Paris-compliant decarbonisation the price per tonne would have to reach $280 on all emissions by 2050.
國際貨幣基金組織估計，要實現(xiàn)符合《巴黎協(xié)定》要求的脫碳，到2050年，所有排放的碳價必須達到每噸280美元。
That, the fund drily notes, “might be politically unpalatable in many countries, despite carbon pricing’s effectiveness”.
國際貨幣基金組織諷刺地指出，“盡管碳定價具有有效性，但這可能在政治上令許多國家心中不快”。
A third way to establish a price is to find people willing to be paid not to emit, thus “offsetting” the emissions of those who do.
第三種確定價格的方法是，找到那些愿意有償不排放的人，從而“抵消”其他人的排放。
This has various practical drawbacks and two fundamental flaws.
這有各種實際缺陷和兩個根本缺陷。
One is that offsetting is voluntary; no one has to do it.
其一，抵消是自愿的; 沒人非得這么做。
The second is that offset emissions are still emissions.
第二，抵消排放仍然是排放。
They still warm the planet.
它們仍然在使地球變暖。
CDR avoids the second problem.
二氧化碳脫除避免了第二個問題。
If a tonne of carbon dioxide is removed from the atmosphere in one place at the same time as another is emitted somewhere else, the harm done is pretty much zero.
如果把一噸二氧化碳從一個地方的大氣中移除，同時在其他地方排放另一噸二氧化碳，那么造成的危害幾乎為零。
Unfortunately, the costs of removal are currently a lot higher than the estimates of the social cost of carbon favoured by governments or the prices charged in cap-and-trade schemes; they outstrip offset prices over a hundred-fold.
不幸的是，目前清除碳排放的成本遠遠高于政府所青睞的碳排放社會成本估計，或者高于限額與交易計劃所收取的價格; 它們比抵消價格高出100多倍。
The idea of a market where the cost of emitting carbon dioxide is the price you have to pay to have it removed is very appealing.
在市場中，排放二氧化碳的成本等于你必須支付的去除二氧化碳的價格，這種想法非常有吸引力。
Actually creating one will be very hard.
實際上首創(chuàng)這一舉動將是非常困難的。
