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年的總統大選終結了“垃圾科學”在美國首都的主導地位。采取有意義的行動，應對氣候變化的幾率——或許通過實施排放物的“總量管制和交易” 制度（cap-and-trade）——已經陡然增加。

但是，這一行動的反對者聲稱，限制溫室氣體排放將使美國經濟受到毀滅性打擊。因此，非常值得指出的是，正如否認氣候正在變化這一事實是垃圾科學一樣，那種認為一旦我們針對氣候變化采取某種行動，就會導致經濟災難降臨的預測，是垃圾經濟學。

是的，限制排放是有代價的。當我這樣一位“持有證書”的經濟學家聽到“綠色經濟”的熱衷者信誓旦旦地說，保護環境是“只有收益，沒有付出”的美事時，我便不由得打起了哆嗦。

但是，現有的最好估計顯示，只要我們分步驟地實施溫室氣體排放限制計劃，它的成本便是適度的。同時，現在致力于這一計劃，的確有可能幫助經濟從當前的衰退中擺脫出來。

首先談論一下成本。

“總量管制和交易” 制度會提高任何一種直接，或間接導致化石燃料燃燒的事物的價格。尤其是，電會變得更加昂貴，因為這么多代人以來，電都是燃煤發電廠生產出來的。

電力部門可以通過限制二氧化碳排放量的方式，減少它們購買“排放許可權”的需要——當然， “總量管制和交易”制度的要旨就是激勵它們這樣做。但是，電力行業為了限制排放而采取的各種措施——例如，轉向其他能源、捕獲并隔離它們排放的大量二氧化碳——無疑會提高其運營成本。

如果“排放許可權”被拍賣的話（理應如此），可以用拍賣所得給予消費者一些折扣，或者減少其他的稅收，這樣做可以部分抵消價格增長的影響。但是，這種補償是不完全的。與沒有氣候變化政策的情況相比，消費者最終的開支要更多。

但是，到底會多開支多少呢？不會很多，包括美國環保署（Environmental Protection Agency），以及麻省理工學院（MIT）“排放預測和政策分析小組”在內的一些審慎的研究者作出這樣的表示。MIT小組的研究表明，即使實施嚴苛的限制，美國人在2050年的消費量也只會比沒有排放限制的消費量，少2個百分點。這依然會給生活標準的巨大提升留下空間，這樣做僅僅會使經濟的年均增速減少二十分之一個百分點。

當然，有許多人堅稱成本要大得多。然而，奇怪的是，這樣的斷言幾乎總是來自那些自由市場經濟的信奉者——這些人聲稱，他們相信自由市場經濟具有無與倫比的靈活性和創造性；它可以輕而易舉地擺脫世界上有限的原油、耕地和淡水資源施加的限制。

那么，他們為什么不相信美國經濟有能力應對溫室氣體的排放限制呢？在“總量管制和交易” 制度下，排放權只不過是另一種稀缺資源而已，在經濟學術語上，這與耕地的供應并沒有什么不同之處。

不必說，像紐特·金里奇（Newt Gingrich）這樣的人——他說，“總量管制和交易” 制度將“懲罰美國民眾”——并不是這么想的。他們只是認為，“資本主義是好的，政府是壞的”。但是，如果你真得信奉市場的魔力，你也應該相信，美國經濟應對排放限制的能力是沒有問題的。

所以說，我們完全有能力承受一項堅定的氣候變化政策。同時，致力于這樣的政策，對于當前身處經濟困境的我們來說，確實大有裨益。

此刻，美國經濟面臨的最大問題是不斷下挫的商業投資。在房市崩盤和虛弱的消費需求的影響下，許多企業深受產能過剩的困擾。面對這樣的局面，它們找不到投資的理由。

但是，假設國會頒布法令，要求從現在起2年或3年之后，開始逐漸收緊排放限制，又會如何？這樣做，并不會即刻對價格產生影響。然而，這會對新投資（比如，對低排放的發電廠、以及節能工廠的投資等等）產生顯著的激勵效應。

換言之，致力于溫室氣體減少，在中短期，將會產生與重大的技術革新相同的經濟效果：它將給予企業一個投資新設備和設施的理由，即便它們面臨產能過剩的問題。鑒于經濟當前的癥狀，這正是它所需要的。

對經濟的短期推動，并非采取氣候變化政策的主要理由。重要的是，地球正處于危險之中，我們等待的時間越長，危情便會越嚴重。但是，這是迅速采取行動的一項額外的原因。

那么，我們有能力拯救地球嗎？是的，我們能。而現在，正是開始行動的絕佳時機。