China's rise in power is surely real, but I don't worry that China will supplant us as a global superpower. That's because China faces the tyranny of proximity.
That is, China faces powerful potential and actual opponents right on their doorstep, which will be powerful blocks to China replacing us as the top power. In addition to questions of whether China can remain united under their communist party, their relative power may not be as significant as their actual increase in power given the power of their neighbors:
As a result of such geopolitical counter-balancing, China will be unable to become a hegemon in Asia--a power with complete dominance over its regional rivals. By definition, a country cannot become a global superpower unless it is also a regional hegemon, such as the United States. As a great power hemmed in by powerful and vigilant neighbours, China must constantly watch its back while trying to project power and influence on the global stage.
Such a status--a globally influential great power, but not a dominant superpower--is something nobody should dismiss lightly. Pax Americana is an accident of history that cannot be copied by another country. For the world, it should not be obsessed by the fear that China will become another superpower. Instead, it should learn to live with China as a great power.
I looked at the issue of relative power comparisons between America and China here.
And worse for China, the general increase in power in Asia--which means that Asian powers can now use their military power to significantly harm other nations in the region--also means that our uncommitted power is even more important in swinging the balance of power:
As long as Asian powers were basically large masses of territory and people difficult to conquer from sheer size, but lacking offensive power, Asian powers didn't need to fear each other nearly as much.
But with Asian powers gaining the offensive conventional military power to threaten each other, they may need the help of another power. And as I noted in the post linked above, we retain the greatest amount of uncommitted and deployable military power on the planet.
Look, I don't deny we could lose our global dominance. Nothing is permanent. But I don't see China taking the title from us. Unless we wreck our position ourselves, of course. I don't rule that out.
UPDATE: I'm pretty sure I've linked or commented on this Stratfor report before, but it bears repeating in its analysis of America, Russia, China, and Europe in regard to geography and economic potential. The tyranny of geography, I suppose. Don't write us off.