The 2008 election ended the reign of junk science in our nation’s capital, and the chances of meaningful action on climate change, probably through a cap-and-trade system on emissions, have risen sharply.

But the opponents of action claim that limiting emissions would have devastating effects on the U.S. economy. So it’s important to understand that just as denials that climate change is happening are junk science, predictions of economic disaster if we try to do anything about climate change are junk economics.

Yes, limiting emissions would have its costs. As a card-carrying economist, I cringe when “green economy” enthusiasts insist that protecting the environment would be all gain, no pain.

But the best available estimates suggest that the costs of an emissions-limitation program would be modest, as long as it’s implemented gradually. And committing ourselves now might actually help the economy recover from its current slump.

Let’s talk first about those costs.

A cap-and-trade system would raise the price of anything that, directly or indirectly, leads to the burning of fossil fuels. Electricity, in particular, would become more expensive, since so much generation takes place in coal-fired plants.

Electric utilities could reduce their need to purchase permits by limiting their emissions of carbon dioxide — and the whole point of cap-and-trade is, of course, to give them an incentive to do just that. But the steps they would take to limit emissions, such as shifting to other energy sources or capturing and sequestering much of the carbon dioxide they emit, would without question raise their costs.

If emission permits were auctioned off — as they should be — the revenue thus raised could be used to give consumers rebates or reduce other taxes, partially offsetting the higher prices. But the offset wouldn’t be complete. Consumers would end up poorer than they would have been without a climate-change policy.

But how much poorer? Not much, say careful researchers, like those at the Environmental Protection Agency or the Emissions Prediction and Policy Analysis Group at the Massachusetts Institute of Technology. Even with stringent limits, says the M.I.T. group, Americans would consume only 2 percent less in 2050 than they would have in the absence of emission limits. That would still leave room for a large rise in the standard of living, shaving only one-twentieth of a percentage point off the average annual growth rate.

To be sure, there are many who insist that the costs would be much higher. Strange to say, however, such assertions nearly always come from people who claim to believe that free-market economies are wonderfully flexible and innovative, that they can easily transcend any constraints imposed by the world’s limited resources of crude oil, arable land or fresh water.

So why don’t they think the economy can cope with limits on greenhouse gas emissions? Under cap-and-trade, emission rights would just be another scarce resource, no different in economic terms from the supply of arable land.

Needless to say, people like Newt Gingrich, who says that cap-and-trade would “punish the American people,” aren’t thinking that way. They’re just thinking “capitalism good, government bad.” But if you really believe in the magic of the marketplace, you should also believe that the economy can handle emission limits just fine.

So we can afford a strong climate change policy. And committing ourselves to such a policy might actually help us in our current economic predicament.

Right now, the biggest problem facing our economy is plunging business investment. Businesses see no reason to invest, since they’re awash in excess capacity, thanks to the housing bust and weak consumer demand.

But suppose that Congress were to mandate gradually tightening emission limits, starting two or three years from now. This would have no immediate effect on prices. It would, however, create major incentives for new investment — investment in low-emission power plants, in energy-efficient factories and more.

To put it another way, a commitment to greenhouse gas reduction would, in the short-to-medium run, have the same economic effects as a major technological innovation: It would give businesses a reason to invest in new equipment and facilities even in the face of excess capacity. And given the current state of the economy, that’s just what the doctor ordered.

This short-run economic boost isn’t the main reason to move on climate-change policy. The important thing is that the planet is in danger, and the longer we wait the worse it gets. But it is an extra reason to move quickly.

So can we afford to save the planet? Yes, we can. And now would be a very good time to get started.

2008年的总统大选终结了“垃圾科学”在美国首都的主导地位。采取有意义的行动，应对气候变化的几率——或许通过实施排放物的“总量管制和交易” 制度（cap-and-trade）——已经陡然增加。

但是，这一行动的反对者声称，限制温室气体排放将使美国经济受到毁灭性打击。因此，非常值得指出的是，正如否认气候正在变化这一事实是垃圾科学一样，那种认为一旦我们针对气候变化采取某种行动，就会导致经济灾难降临的预测，是垃圾经济学。

是的，限制排放是有代价的。当我这样一位“持有证书”的经济学家听到“绿色经济”的热衷者信誓旦旦地说，保护环境是“只有收益，没有付出”的美事时，我便不由得打起了哆嗦。

但是，现有的最好估计显示，只要我们分步骤地实施温室气体排放限制计划，它的成本便是适度的。同时，现在致力于这一计划，的确有可能帮助经济从当前的衰退中摆脱出来。

首先谈论一下成本。

“总量管制和交易” 制度会提高任何一种直接，或间接导致化石燃料燃烧的事物的价格。尤其是，电会变得更加昂贵，因为这么多代人以来，电都是燃煤发电厂生产出来的。

电力部门可以通过限制二氧化碳排放量的方式，减少它们购买“排放许可权”的需要——当然， “总量管制和交易”制度的要旨就是激励它们这样做。但是，电力行业为了限制排放而采取的各种措施——例如，转向其他能源、捕获并隔离它们排放的大量二氧化碳——无疑会提高其运营成本。

如果“排放许可权”被拍卖的话（理应如此），可以用拍卖所得给予消费者一些折扣，或者减少其他的税收，这样做可以部分抵消价格增长的影响。但是，这种补偿是不完全的。与没有气候变化政策的情况相比，消费者最终的开支要更多。

但是，到底会多开支多少呢？不会很多，包括美国环保署（Environmental Protection Agency），以及麻省理工学院（MIT）“排放预测和政策分析小组”在内的一些审慎的研究者作出这样的表示。MIT小组的研究表明，即使实施严苛的限制，美国人在2050年的消费量也只会比没有排放限制的消费量，少2个百分点。这依然会给生活标准的巨大提升留下空间，这样做仅仅会使经济的年均增速减少二十分之一个百分点。

当然，有许多人坚称成本要大得多。然而，奇怪的是，这样的断言几乎总是来自那些自由市场经济的信奉者——这些人声称，他们相信自由市场经济具有无与伦比的灵活性和创造性；它可以轻而易举地摆脱世界上有限的原油、耕地和淡水资源施加的限制。

那么，他们为什么不相信美国经济有能力应对温室气体的排放限制呢？在“总量管制和交易” 制度下，排放权只不过是另一种稀缺资源而已，在经济学术语上，这与耕地的供应并没有什么不同之处。

不必说，像纽特·金里奇（Newt Gingrich）这样的人——他说，“总量管制和交易” 制度将“惩罚美国民众”——并不是这么想的。他们只是认为，“资本主义是好的，政府是坏的”。但是，如果你真得信奉市场的魔力，你也应该相信，美国经济应对排放限制的能力是没有问题的。

所以说，我们完全有能力承受一项坚定的气候变化政策。同时，致力于这样的政策，对于当前身处经济困境的我们来说，确实大有裨益。

此刻，美国经济面临的最大问题是不断下挫的商业投资。在房市崩盘和虚弱的消费需求的影响下，许多企业深受产能过剩的困扰。面对这样的局面，它们找不到投资的理由。

但是，假设国会颁布法令，要求从现在起2年或3年之后，开始逐渐收紧排放限制，又会如何？这样做，并不会即刻对价格产生影响。然而，这会对新投资（比如，对低排放的发电厂、以及节能工厂的投资等等）产生显著的激励效应。

换言之，致力于温室气体减少，在中短期，将会产生与重大的技术革新相同的经济效果：它将给予企业一个投资新设备和设施的理由，即便它们面临产能过剩的问题。鉴于经济当前的症状，这正是它所需要的。

对经济的短期推动，并非采取气候变化政策的主要理由。重要的是，地球正处于危险之中，我们等待的时间越长，危情便会越严重。但是，这是迅速采取行动的一项额外的原因。

那么，我们有能力拯救地球吗？是的，我们能。而现在，正是开始行动的绝佳时机。