Ever since the financial crisis, we have heard a great deal about how the world's economic centre of gravity is shifting.
The United States and Europe are in decline, their economies hamstrung by crippling public debt burdens.
Meanwhile, Asia is rising, propelled by the emergence of China as a trading and financial superpower.
It is a compelling narrative, adored by the party bigwigs in Beijing and ardently promoted by companies like HSBC that derive much of their profit from the region.
Reality is seldom so neat. Even as Asia - and China especially - is gaining ground in its relative economic importance, a second shift is taking place in the world economy that will greatly complicate the first.
Take a look at the first chart. The black line shows how many billion cubic feet of natural gas the US produces each day. The red line shows how many million barrels of crude oil it pumps out of the ground. Thanks to technological advances allowing the exploitation of hydrocarbon deposits locked in giant formations of shale, US natural gas production has soared by more than a third since 2005. Crude oil production has shot up by a quarter since 2008.
As the International Energy Agency made clear in a report published on Monday, this surge in US oil and gas output is a game-changer for global energy markets.
At the moment, the US imports about 20 per cent of its energy needs. But with new shale oil deposits in America's mid-west coming on stream, the IEA expects the US to overtake Saudi Arabia to become the world's biggest oil producer by 2020.
With shale gas production also ballooning, natural gas will far outstrip oil and coal to become the dominant energy source in the US. As a result, the IEA predicts that the US will achieve effective energy self-sufficiency, with North America as a whole becoming a net exporter of oil by 2030.
This shift will change things far beyond the energy markets, fundamentally altering economic - and strategic - relationships around the world.
For a start, consider the impact on the US trade and current-account deficits. For years, America's import demand and its resulting overdraft with the rest of the world have been among the most powerful forces determining the world's economic trajectory.
But much of that import demand has been for energy. As the second chart shows, since the financial crisis erupted in 2007, the share of energy imports in the US trade deficit has doubled, with oil imports now accounting for 60 per cent of the overall deficit.
If those oil imports now evaporate entirely as the IEA projects, the US trade deficit could fall to near-negligible levels over the coming years.
Its trade balance could even swing into surplus. In recent years, manufacturers have relocated from the US to China to take advantage of cheap labour, subsidised energy and cut-price land. Now, with incomes rising fast, China's labour-cost advantage is being eroded.
With capital costs in the US about half those in China, some manufacturers are already considering a return. In the future, as chronic water shortages impose an energy squeeze on China, and as the US continues to enjoy its shale gas-fired cheap energy boom, they will have an even greater incentive to manufacture in the US rather than Asia.
If the US does rebalance in this way, it will inevitably force rebalancing on economies elsewhere. China's trade surplus could swing into deficit, and its growth rate slow even more than expected in future years.
That will not reverse the relative shift we can see in the world's economy towards Asia, but it will make the neat narrative of US decline and Asian ascendance a lot more complicated.Topics: Global economy Natural Gas Crude Oil