Stuart Gaffin is a climate researcher at Columbia University  and is a regular contributor with his blog “Exhausted Earth”. ThomsonReuters is not responsible for the content - the views are the author’s alone.

On April 16 President Bush gave a speech laying out a new United States climate policy goal - stabilizing US emissions by the year 2025.

During the course of this speech the President reported as progress a previous goal he had announced in 2002: that the “carbon intensity” of the US economy under his administration has been declining at the rate of about 18% per decade — the rate he targeted in 2002. Carbon intensity is the amount of carbon emitted by US fossil fuel combustion per dollar of US economic output.

There has been both just and unjust criticism about using this benchmark for progress on US climate. Just criticism is the fact that the US economy has long been ‘decarbonizing,’ including under the Clinton Administration, at a little less than 18% per decade, without any climate change policies.

The forces driving this include continual improvements in energy efficiency, structural changes in the economy like the growing information technology sector and environmental concerns unrelated to climate, like air pollution control. Therefore the US administration did not make clear to the public the actual meekness of the 2002 goal.

The US administration should not be faulted however for focusing on carbon intensity as a key metric for progress, in addition to total emissions. Carbon intensity must indeed drop if we are ever going to control emissions. It just has to do so fast enough to offset economic growth.

So, for example, the new goal of stabilizing US emissions in 2025 simply means carbon intensity has to decline at the same rate as US economic growth then: if the economy is growing at say 3%, then carbon intensity must decline at 3%. Eventually, to bring actual US emissions down, the intensity will have to decline at a faster rate than the economy is growing.

There is nothing wrong with framing climate policy this way (although many do not feel that US emission stabilization in 2025 is enough.)

Indeed, we ought to be speaking much more about carbon intensity so that it attains the same familiarity in the public mind as economic growth rates and population growth rates. It is going to be one of the most important economic and environmental numbers of the 21st century.

There are plenty of ways to get around New York City, not all of them savory — subway, bus, car, taxi, bike, shoe-leather — but few offer the environmental cachet of the plug-in electric motorbike. Sleek, slim and silent, the Vectrix two-seater owned by filmmaker Michael Bergmann is definitely preferable to rocketing around town under almost any other kind of power. The ride from the East Side to the West Side one recent evening was an absolute pleasure, with less ambient noise than a golf cart as we zoomed across Central Park.

“I’ve always felt that enjoying life in New York to the fullest requires a way to get around New York,” Bergmann said later in an e-mail. “A way that’s quiet and up on the surface so you can enjoy the varied life and changing neighborhoods as you travel. That requires a vehicle that’s street legal (so I don’t worry about being stopped or having it confiscated), always available, that isn’t hard to park, that doesn’t contribute to congestion or pollution (air or noise), that can carry the amount of stuff one ordinarily carries, and carry a passenger as well. So as soon as I found out about the Vectrix I wanted one.”

Vectrix, headquartered in Rhode Island, first started selling its electric plug-in motorbikes in Europe and is now expanding in the U.S. market. The company bills its plug-in model as “an advanced zero-emission, battery-powered motorcycle,” with comparable performance to a 400cc gas-powered motorcycle.

Bergmann and his wife Meredith, a sculptor, use the bike as their principal mode of transport around Manhattan. The Vectrix gets parked and plugged in in the underground garage at their apartment house, where they pay for half a parking space, with electricity included. It gets about 40 miles (65 km) to a charge, which is enough to get around New York’s five boroughs, and Michael figures the company’s claim that it can get up to 62 miles (100 km) per hour is accurate, since he’s been able to accelerate uphill on the FDR Drive, no mean feat.

Bergmann has always been an early adopter of new technology, and he’s no exception here. You can see what he’s done in the film world.

He admits there’s one drawback: the price. His model cost $11,000. But he reckons that, because of where and how he and his wife live, “it will pay for itself in taxis not taken in two years.”

Stuart Gaffin is a climate researcher at Columbia University and will be a regular contributor with his blog “Exhausted Earth”. Reuters is not responsible for the content — the views expressed are the author’s alone.

The root cause of all environmental problems-from beer cans floating on a lake to global warming-can be explained using the following two contrasting scenes:

Scene 1: We are sitting in an automobile inside a small, closed garage.

You are in the passenger seat and I am at the wheel. We are waiting for a third passenger from inside the building. Suddenly I reach for the ignition and turn the engine on. Alarmed by the thought of being poisoned by the exhaust, your eyes widen in amazement as you say, “What are you doing?” When you reach to turn the ignition off, I block your hands and soon a life-and-death struggle begins for control of the vehicle. You are screaming: “Are you crazy! You’re going to kill us both!”  If we manage to survive the episode you will seek to have me put under psychiatric care. Heck, I might even end up in prison for attempted manslaughter. My days as an ordinary law-abiding citizen are over.

Scene 2: Exact same situation except that now the car is sitting a mere ten feet back on the driveway outside the garage.

I reach for the ignition and turn the car on. You might look over but you say nothing. The engine could idle 15 minutes or more, but we sit calmly in silence. Our passenger arrives and we drive off. I remain a perfectly well-respected citizen. Indeed if you happened to question me the next day about the engine idling, you’re the one who would probably feel strange.

Economists explain the remarkable difference between scene 1 and 2 as “the tragedy of the commons.” When we pollute a seemingly vast reservoir like the atmosphere (a “common space”) the rapid dilution of our pollution makes us oblivious to what we are doing. Since everyone acts the same self-interested way (the “tragedy”), the pollution accumulates, including carbon dioxide (a greenhouse gas) . If instead, we were forced to inhale all of our own emissions, we would stop this behavior immediately. Since this is never the case, the economic solution is a pollution tax.

Throwing a beer can on a lake is the same thing-the can soon floats away so you don’t have to look at it. But if everyone were to toss empty cans into the same lake, it would soon be blanketed in tin. Who would be responsible for cleaning up the lake? Would it be fair to ask all residents to foot the bill, or just the individual polluters? The same question exists with global warming and greenhouse gas emissions: If rich countries alone were forced to absorb all the impacts of their emissions, we’d have seen a lot more action by now. Instead, less developed countries have the dubious privilege of sharing the impacts.

What makes the oblivion brought on by the commons so extreme that, like with an engine idling, the polluting behavior becomes the “norm” and questioning it feels almost “abnormal”? 

For example, how would you feel asking a stranger to turn off his idling car? How would you react if you had to pay for how much pollution your car emitted while you were idling?