We are undoubtedly entering a historic period in the annals of climate history.

Momentum is building toward the Copenhagen climate negotiations in December, where-many hope-the nuts and bolts of a new international climate change framework will be negotiated. There is a growing sense of optimism in the air. Some are hopeful that, this time, the international community will actually forge a workable climate treaty. The source of this optimism? For one, the world has learned its lessons from past failures, including the Kyoto Protocol and a number of regional initiatives (such as Phase One of the European Emissions Trading System, ETS). Furthermore, thanks to continued scientific research and concerted efforts to inform policymakers and the public, the science of climate change has become ever starker; the policy options, clearer; and the willingness to include critical sectors like deforestation and land-use change, much stronger.

But perhaps most importantly, this time the United States may finally be on board.

This marks a remarkable sea-change for a country that, just three years ago, had a President whose official stance on global warming was flippant if not blatant denial. The dramatic shift of tide is exemplified by the recent and historic passage of the ACESA (American Clean Energy and Security Act, 2009) in the House of Representatives. Though by no means a perfect bill, it sets a declining cap on carbon emissions. Total greenhouse gas emissions will be reduced to 17% below 2005 levels by 2020 and 73% below 2005 levels by 2050[1]. The scale of proposed reductions, though not particularly ambitious, is still probably compatible with staying within 2 degrees Celsius (C°) or fewer of planetary warming by 2100[2]. The heart of the plan is a cap-and-trade scheme that would induce an economically efficient reorientation of the American economy toward a more climate-friendly trajectory. According to some estimates, all of this could be achieved at the price of mere pennies a day for the average American consumer[3]. Until this year, not a single bill proposing concrete action had gathered anything close to the number of votes needed for passage in either the House or the Senate.

And despite the necessarily domestic scope of the bill-it only imposes caps on U.S. emissions-it is clear that domestic action on climate change has profound international implications. Many believe it is critical for the U.S. to have an established domestic commitment on climate change in order for it to have a real say at the negotiations in Copenhagen. After all, compared to many other countries in the rich world, the U.S. is embarrassingly late to the game. The European Union is already in the second iteration of its European Emissions Trading scheme (ETS), and has recently announced an EU-wide target of 20% reduction in greenhouse gases and a 20% share of renewable energy in total energy consumption by 2020[4]. Japan and Canada have also expressed similar goals and set up voluntary carbon markets domestically. Even Brazil has committed to a 70% reduction in deforestation-and the emissions that result from it-by 2018. By establishing a domestic cap-and-trade system for carbon, the U.S. may finally send the signal to other countries that it is serious about climate change.

If indeed the U.S. is taking climate mitigation seriously, it comes not a moment too soon. Despite the sheer difficulty of long-term climate projections, it is becoming increasingly clear that the consequences of “business-as-usual” are profoundly bleak, and that the costs of delay could be massive. As the synthesis report of the Copenhagen Climate Congress illustrates, the damages associated with rising temperatures may be much greater than previously estimated and will only grow with longer inaction. Postponement of mitigation entails greater and more rapid temperature increases, higher adaptation costs, and the locking in of high-carbon infrastructure that delays clean technological development and makes it more costly overall[5]. Furthermore, delay in curbing emissions increases the danger of irreversible “climate shocks”-the melting of the Greenland ice sheet, for example-that could adversely affect the global economy in a very serious way. Indeed, the new report suggests that the warming scenarios for business-as-usual appear more likely to be on the higher end of previous projections, meaning greater potential for catastrophic damages than scientists had expected before.

A growing number of world leaders, policymakers, and even businesses-not just in the rich world but in developing countries too-are becoming increasingly aware of these risks, as well as the rewards for acting sooner rather than later. They are calling for immediate action. Many seem willing to get going with economically feasible carbon-saving projects on the ground-the so-called “low-hanging fruit”-even in the absence of an overarching international framework. Indeed, there are many emissions-reducing solutions like insulation improvements, sugarcane biofuels, and energy efficiency improvements of old appliances that have a negative net cost of deployment (relative to existing uses or technologies). That is, they make economic sense even without an international carbon market[6]. In most cases, the barriers to adoption of these technologies are mostly informational (people just don’t know about them), inertial (old habits die hard), or financial (some people, especially in developing countries, don’t have access to the credit necessary to make the up-front investment). These are projects that we can get started on regardless of what happens in international talks. The UN Foundation, along with many other NGOs, is currently pushing for just that with its “building blocks” approach[7].

But most countries seem to be waiting for America to take the lead in achieving an international agreement-a viable successor to the Kyoto Protocol.

This makes the passage of ACESA all the more critical. If it is approved by the Senate and enacted into law by President Obama, the ACESA would finally put the U.S. on a path of declining emissions and would no doubt motivate many other countries (notably China, now by volume the world’s largest emitter) to follow. It would make a working international agreement in Copenhagen much more likely.

These are big ifs. In the Senate, the bill will most likely require a 60 vote majority to pass without a filibuster. Considering the much stronger rural bias in the Senate and the sway of energy lobbies in coal-rich Southern states, this passage will not come easily.

But a no-vote on this bill would be a signal to the world that the U.S. still does not recognize the urgency of climate change mitigation. In that case, there is little chance that developing countries such as China and India will find it politically feasible to sign on. Their line of argument is quite predictable: “You guys are responsible for most of the greenhouse gases in the atmosphere to date. We are still trying to play developmental catch-up. Why should we do sign on to mandatory reductions when you, the richest country in the world, won’t?” If the U.S. has no internal commitment to cut carbon, this point would be hard to rebut.

Yet, on the flip side, the size and scale of America’s potential carbon market means that passing a domestic cap-and-trade bill now would give the U.S. tremendous leverage, putting the ball squarely in the developing countries’ court. As Nathaniel Keohane of Environmental Defense Fund (EDF) puts it, if the United States signals that it is committing to emissions reductions now, others will perceive that “the train is finally leaving the station, and everyone will be haggling over the terms on which they will board it, rather than waiting to see what we do.”

Clearly, a lot is at stake in the next few months’ Senate hearings. There is a pressing need for ordinary citizens-the general public-to be more vocal. On an issue as pervasive and inter-generational as climate change, it is our responsibility not to simply stay mum. The reason why legislation in the U.S. has historically been so hard to pass- even the House bill passed by the slimmest of margins, 219 to 212-is not because there is any real debate over the need for curbing climate change. Rather, most of the obstacles are imposed by vested interests trying to minimize their share of the burden. Lobbies from coal and oil companies that stand to lose out from such a bill are the ones who yell the loudest in opposition (and financially can afford to send their envoys to Washington). Politicians naturally hear them. What politicians seem to have a harder time hearing is the diffuse yet pervasive appeal of the average citizen who knows she will end up footing the bill both for the costs of containing climate change and the damages that it will wreak if left unchecked.

So what to do?

We must demand that the current climate bill does not get watered down in the Senate by more concessions to industry and coal lobbies. Politicians and policymakers feel it when the public eye (and ire) is on them. They are just as likely to dodge hard choices when our attention wanders elsewhere. Referring to the necessity of getting this bill passed, Thomas Friedman, columnist for the New York Times, makes a particularly impassioned appeal: “You want to make a difference? Then get out of Facebook and into somebody’s face. Get a million people on the Washington Mall calling for a price on carbon. That will get the Senate’s attention. Play hardball or don’t play at all.”

He is right. These are matters that will determine the state of the planet for decades to come, with profound consequences for current as well as future generations. There is not a single person alive today who does not have a stake in tackling climate change. It is incumbent on all of us to care.

[2] That is, assuming that other countries carry through with their existing pledges, and developing countries eventually sign on to some cuts as well, sometime around 2020.

[3] A recent report by Nathaniel Keohane and Peter Goldmark of EDF finds that, for the US, the median impact on annual GDP growth of capping greenhouse gases amounts to three-hundredths of a percentage point (0.03%), or less than 1% of average household spending (Keohane, 2008).  An analysis by the State Department shows similar findings.

[4] European Union: http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2009:140:0063:0087:EN:PDF

[5] See Synthesis Report – Climate Change: Global Risks, Challenges and Decisions. Copenhagen 2009.

[6] See: McKinsey Co. “A Cost Curve for greenhouse gas reduction” 2005.

[7] For more details, see: “Practical Strategies for immediate progress on climate change” at www.unfoundation.org