Can you say guilt trip? New Yorkers will now be reminded of humanity’s growing carbon footprint as they hustle past Madison Square Garden and Penn Station.

Starting this morning, a 70-foot sign with a 13-character red digital display is tracking the trillions of tons of greenhouse gases roiling the atmosphere.

Climate heavyweights Jeffrey Sachs of Columbia University and John Reilly of the Massachusetts Institute of Technology were on hand for the rainy unveiling.

The counter is the work of scientists from around the country. But it also serves as an advertisement of sorts for sponsor Deutsche Bank, whose Climate Change Advisors group aims to help various industries profit from a low-carbon economy.

That’s not to say the science behind the counter is anything to sneeze at. Economist Reilly mentioned the technical challenge of creating a real-time counter using economic indicators and other data, which are validated and adjusted as updated gas measurements become available.

The counter takes into account all greenhouse gases, including carbon dioxide, methane, and nitrous oxide, and reports them in carbon dioxide equivalents. It skips the effects of natural cycles, such as the El Niño, and doesn’t factor in aerosols, which are difficult to measure and also exert a cooling effect.

After Reilly left the stage, the counter remained dark as rain pelted the white press tent. Then, Sachs took the mic and cracked the downpour was only appropriate because a recently released government report on climate change forecasts rainier weather in the Northeast.

Finally, the switch was flipped, and the 13-digit number appeared. The last three digits were a red blur. Someone under the crowded tent blurted, “Is it going up?” and the journalists laughed.

Later, caught up with some locals for their reaction. A busy umbrella hawker said he wasn’t interested in the carbon counter, even after we told him rising greenhouse gases might help his business.

David Roberts, a managing partner at a company that makes software for book publishers, was impressed and humbled by the clock.  “That’s startling,” he said, “How do you miss that?”

Under a nearby awning, Shawna Unger, a 35-year-old employee of publisher McGraw-Hill, was having a quick smoke. She was unaware of the clock until we mentioned it to her, but she said rising greenhouse gases worry her. Is she going to do anything about climate change? “I have those long-lasting light bulbs,” she said, “The long twirly fluorescent ones.”

UPDATE (16:10): According to Deutsche Bank, the counter is carbon neutral and its power consumption is offset with Certified Emission Reductions, or CERS.  It contains 40,960 energy efficient light emitting diodes, which use 83 percent less power per pixel than the news ticker Dow Jones installed in Times Square in 1997.  The counter is powered from the city grid, but representatives did not have information on its total power consumption.  Also, when this article was originally posted it provided an incorrect estimate of the height.

Image of carbon counter by Brendan Borrell/Scientific American