'China vows to reduce emission levels,' echoed Canada's National Post.

Certainly, if Hu really had made a promise to cut China's greenhouse gas emissions, it would have been big news.

But he didn't do anything of the sort.

What Hu actually said was 'we will endeavour to cut carbon dioxide emissions per unit of GDP by a notable margin by 2020 from the 2005 level'.

That's a different thing entirely.

Hu didn't promise to cut China's greenhouse gas emissions, merely the gases it emits to produce each unit of economic output.

In other words, all he pledged was that China's greenhouse gas emissions would not grow as fast as its economy.

That's not much of a pledge. Take a look at the first chart below, which comes from Rajesh Panjwani at CLSA.

Thanks to its dependence on coal and the inefficiency of its power plants, China's greenhouse gas emissions per unit of output are by far the highest among the world's big economies.

So all Beijing has to do to reduce its emissions per unit of gross domestic product is to boost its energy efficiency and raise the proportion of power sources other than coal in its energy mix.

This is exactly what China is doing already in an attempt to raise its competitiveness and bolster energy security.

As a result, over the past 10 years, China's GDP has grown at an average pace of 9 per cent annually, while according to data from BP, its greenhouse gas emissions have grown at 7 per cent.

So China has already reduced carbon dioxide emissions per unit of GDP by a notable margin. Except that over the same period, China's carbon dioxide emissions have more than doubled in absolute terms.

Unfortunately, what matters for global warming is not relative emission levels but the absolute amount of greenhouse gases pumped into the atmosphere.

That's bad news for the future of our planet. Let's suppose for a moment that the developed world succeeds in reducing its emissions by 2 per cent a year for the next 10 years to cut its output of greenhouse gases to 22 per cent below the 2005 level by 2020.

And let's assume that China's economy grows at Beijing's annual target rate of 8 per cent a year for the next 10 years, while the growth in its greenhouse gas emissions slows to 6 per cent annually.

Hu will have fulfilled his promise. But China's greenhouse gas emissions will have doubled again by 2020. And the increase in its emissions will far outweigh the cuts made by the developed countries. So even if discharges from the rest of the world remain steady at 2008 levels, overall global emissions will still have increased 21 per cent compared with 2005 levels.

In other words, it doesn't matter what developed countries do. Unless China climbs on board and agrees now that the absolute level of its greenhouse gas emissions must reach a peak at a set date and fall after that, there will be little hope of halting, or even slowing, global warming.

That might sound like an unfair demand to make of a developing economy with a large population. But as the second chart below shows, China's greenhouse gas emissions per head are already higher than the global average and are fast gaining on those of developed countries like France.

In his speech last week, Hu said China is 'fully aware of the importance and urgency of dealing with climate change'.

If that's the case, he should go a step further and agree that China's emissions should reach a definite ceiling by 2020 and begin to fall after that.

Then he really would be the climate change hero that the media made him out to be last week.