The global interest in China's actual GDP on a comparative scale is to help estimate things like their future consumption of natural resources, their threat to global stability, and to evaluate global recessions/growth more accurately.
The problem with "seeing it" is differentiating what you are seeing with what is. So for example a city in the US that has a lot of large buildings being built is a clear sign of economic growth because the market dynamics are structured so that people don't build buildings unless they believe they can rent them out profitably, so they 'lead' in the sense there is demand for that space, they go up, it gets rented, and now there are a bunch of new jobs in the city which brings in workers with wages etc etc etc.
But in China there are buildings that were built simply because the government said "Build a building." There are buildings that are totally empty (see this link http://io9.com/chinas-brand-new-abandoned-cities-could-be-dy... which has some fascinating pictures).
So people don't trust the economic statistics the government produces and seek out other ways of either confirming or denying what is said. Energy consumption is one such indicator which, when combined with a technology sophistication index, can provide another data point on China's economic strength.
As comments to your first comment have already pointed out, pollution per unit of primary energy produced in power plants can vary wildly among different parts of the world. Yes, we know that China is putting up a lot of buildings. We know that China has huge amounts of air pollution. We don't know if China would be doing either of those things to the same degree if China had a freer market and more effective rule of law. That's why observers like me think that China could still stagnate at its current level of economic development, and lose the growth magic that it (undeniably) has enjoyed during most of our adult lives.
The global interest in China's actual GDP on a comparative scale is to help estimate things like their future consumption of natural resources, their threat to global stability, and to evaluate global recessions/growth more accurately.
The problem with "seeing it" is differentiating what you are seeing with what is. So for example a city in the US that has a lot of large buildings being built is a clear sign of economic growth because the market dynamics are structured so that people don't build buildings unless they believe they can rent them out profitably, so they 'lead' in the sense there is demand for that space, they go up, it gets rented, and now there are a bunch of new jobs in the city which brings in workers with wages etc etc etc.
But in China there are buildings that were built simply because the government said "Build a building." There are buildings that are totally empty (see this link http://io9.com/chinas-brand-new-abandoned-cities-could-be-dy... which has some fascinating pictures).
So people don't trust the economic statistics the government produces and seek out other ways of either confirming or denying what is said. Energy consumption is one such indicator which, when combined with a technology sophistication index, can provide another data point on China's economic strength.