Alberto Ades, co-head of global economics research at BofA Merrill Lynch, estimates that given their combined size, a one percentage point drop in the GDP of emerging markets is the equivalent of a 1.7 point fall in the U.S. He predicts developing economies will expand 5.3 percent this year, down from a 5.5 percent estimate at the start of the year.

"When you think about emerging markets driving growth, what happens to them is pretty significant," he said in a telephone interview.

Policy makers are responding where they can. China last week cut borrowing costs for the first time since 2008, while Brazil's central bank has signaled it will reduce its benchmark rate for an eighth straight time in July after cutting it to a record low 8.5 percent in May.

China may also introduce additional stimulus to protect its growth target, and Indian Prime Minister Manmohan Singh on June 6 outlined initiatives including port projects worth $6.3 billion.

And a conclusion by Jim O'Neill:

O'Neill, who recently published a book entitled "The Growth Map: Economic Opportunity in the BRICs and Beyond," said he is more concerned by Brazil's weak growth and India's policy paralysis than he is by China, which he says remains on track to become a more consumer-led economy.

He remains "relatively sanguine" that his world view is intact a decade since he and colleagues at Goldman Sachs predicted that the countries would join the U.S. and Japan as the world's biggest economies by 2050. The BRICs moved from 11 percent of global GDP in 1990 to about 25 percent in 2011 and are on course to reach 40 percent by 2050, Goldman Sachs said in a December report, which also said their potential growth rates may have probably peaked.

"The idea countries always grow at a ridiculous rate was never the case," O'Neill said. "The fact they've been disappointing for one or two quarters is neither here nor there."

David Fuller's view A concern of mine, expressed in this Commentary from time to time and especially our Audios in recent months, was that China and India might be waiting too long before relaxing their earlier tightening bias for monetary policy.

They were understandably concerned by inflationary pressures, knowing that rising commodity prices have been a key source of inflationary pressures over the last decade, generally increasing in line with GDP growth and falling back somewhat when global economic activity slowed.

However inflation is a lagging indicator. Crucially, in my opinion, we have seen an important reset in commodity prices over the last 14 months as you can see on these charts of the Continuous Commodity Index (CCI) (Old CRB) (monthly & weekly), which is unweighted. This has reduced, if not entirely negated, the headwind of commodity price inflation. CCI currently looks somewhat oversold and it has returned to the first clear region of potential support commencing just above 500, evident on the charts above.

Commodity prices remain high compared to 12 or 13 years ago but those were historically depressed levels, unlikely to be seen again, in my opinion, without a much greater economic slump than any mainstream economist is predicting. Central banks have pumped record levels of liquidity into the global economy to lower that risk, as we know. This 20-year chart shows CCI adjusted for US CPI inflation and it is not wildly above levels seen throughout much of the 1990s, considering the emerging market growth since then and the additional demand this has placed on both industrial and agricultural resources.

Crucially, Brent crude oil recently fell beneath its reaction trough seen a year ago, while the WTI contract has retraced most of its gains following last October's low. This gives the growth economies leeway to provide a further stimulus. China, which remains the lead engine for global GDP growth, has seen its inflation decline despite a policy to increase wages in the coastal regions. Most of India's inflation is now due to subsidies, wages and an inability to efficiently transport and store the food it produces.