Let's take a look at the trading in merchandised goods, as an example. (trading in services, although only a quarter of that for goods in value today, is not to be neglected)
According to WTO, world import in 2003 is $7569bn, with a growth rate of 16% (! a jump from 5% in previous years)
For China, export=$438bn, import=$413bn, so China's export market share (addressable) is 438/(7569-413)=6.1%
For Japan, export=$472bn, import=$383bn, export market share (EMS) =6.6%
Germany has EMS=748/(7569-602)=10.7%, USA=11.6%, France=5.4%, Korea=2.6%, Chinese Taipei (Taiwan)=2.0%.
We can see that the export market share for China is still a lot lower than that of Germany or US. For China to catch up with US' share of 11.6%, it will need to grow in an extra 7% for 10 years continuously, riding over the global trading market growth of 5-16%. If we take the medium value of 10% for world average, China's room for growth can be (for example) around 17% p.a. for 10 more years, before it reaches the market share level of the US.
However, if we would boldly assume that when GDP/cap of different nations will converge in the long term, China would get its EMS of around 20% (same as its population share), then China would have 18 years of growth like that (7% on top of global average).
- Japan, with 2% of world population (let's denote it as PS, population share), has 6.6% of EMS, EMS/PS=3.3; US with 5% population for 11.6% EMS, EMS/PS=2.3; Germany's EMS/PS is even higher (7.8). We can postulate that EMS/PS may converge to 1-2 in the future, as developing nations such as China and India catch up
- More likely through, global trade growth will slow down from 16% to maybe 8-12%, gradually. While China's rate to outgrow other nations will decrease from 10% to below 5% gradually as well, i.e. from 20% in 2006-08 down to 15% in 2012-14 if we assume the global average is 10%. (i.e. extra percentage over world average has an average value of 7% over 10-18 years, maybe slower if the number of years it takes to converge to global average is longer)
As China's market share in service sector is still very low (total market size = 1/4 of that of merchandise goods), there is also more potential for growth in the service sectors.
- China's export (in goods) can grow at 7% above world average for another 10-18 years, but no where near the 30% rate in 2004 (unless the global trade grows at 20% p.a., not likely)
- America and Germany have the highest export market share in the world already! Don't complain about your export, there is not much room for growth (perhaps making money by investing in developing countries is easier than boosting export)
- Korea and Taiwan still have plenty of room to grow, much larger than China's, despite its already higher export/GDP and GDP/cap
- While Export/GDP can measure the internal sustainability, EMS is a good measure for external demand and hence sustainability (EMS/PS ratio can also be used as an indicator, but there is no strong reason for it to converge to the value 1, except if one believes productivity would converge, which may not happen in a this millenium)