Deutsche Bank lit a seven-storey-high sign in the middle of Manhattan on Thursday that counts the total amount of greenhouse gases trapped in the Earth's atmosphere.

The bank said it was the world's first sign to show real-time measurement of the gases blamed for global warming and hoped it would spark more public debate on how to reduce emissions.

The giant carbon counter developed by scientists at the Massachusetts Institute of Technology hangs outside Madison Square Garden.

The sign said the current quantity of carbon dioxide in the planet's atmosphere is 3.64 trillion tonnes, the highest level in 800,000 years, and is increasing by 800 tonnes a second.

Reports from the United Nations science panel that assesses data on global warming only come out every five or six years.

If you flipped on one of the news channels that covers the financial news ... and there was a number that was updating once every five years, the commentators would have a hard time finding something to talk about, Kevin Parker, the global head of Deutsche's asset management team, told reporters.

The minute you convert that to a real-time number, it can serve as a backdrop for lots of conversations.

The counter's rapidly changing digital numbers are powered by nearly 41,000 low-energy light emitting diodes.

Deutsche did not sponsor the sign purely for conversational reasons. It conducts research on trading greenhouse gas emissions and has investments in environmental fields.

The launch of the sign was praised by a range of climate leaders, including scientists and nongovernmental groups. One could not resist a stab at carbon markets, which aim to harness the power of capitalism to reward early actors who cut their emissions. The markets can also make bankers very rich.

Trading these permits is a side show, Jeffrey Sachs, the head of Columbia University's Earth Institute, said at an event celebrating the launch of the counter.

Sachs praised the bank for bringing the measurement down to people in street and for helping to set up deals that will encourage the economy to move beyond fossil fuels.

Nature gave its own side show. A rain storm with lashing winds, the type Sachs said can be expect more in coming decades as a result of global warming, made many passers-by pay more attention to their umbrellas than the sign.

(Reporting by Timothy Gardner, editing Anthony Boadle)