Thousands of Nigerian traders and shoppers throng an outdoor market in Oshodi Road in Lagos on April 18, 2003. Juda Ngwenya/Reuters Occasionally, there comes along an opportunity so gigantic that it would be hard to miss.

In a round-up of some of its strongest long-term investing themes, Bank of America Merrill Lynch highlighted one such opportunity for businesses and economic growth: the explosion of the global middle class.

"In a world starved for growth, we believe that the answer lies in uplifting the 4.5 billion people at the base of the economic pyramid," wrote BAML's thematic investing team.

They continued: "These 'Bottom Billions' earn only $1-10/day, but have $5 trillion in purchasing power and $7.4 trillion in wealth."

The note mentions that many of these "Bottom Billions" are young, mainly in urban areas, and technologically connected. Additionally, trends that support consumption and income growth such as education and access to stable housing are on the rise, which should logically lead to an increase in consumer spending for the group.

Add up all of these trends, and you have a shift into the middle class like never before.

"The Bottom Billions will drive the growth of the global middle class, which will expand at rates seen only during the 19th century Industrial Revolution and post-WW2 booms. Every minute, 30 EM households join the global middle class," wrote the BAML team.

They added: "By 2030, the global middle class — households with a daily expenditure of US$10-100 per capita (in purchasing power parity terms) — is expected to grow to 4.9 billion people (+3 billion people)."

This will increase the consumption of the global middle class by leaps and bounds. Based on their estimates, the BAML team estimates that spending by this cohort will leap from $21 trillion in 2009 to $56 trillion in 2030 and $84 trillion by 2050.

Much of the growth will come from emerging markets, according to the note, which should increase their importance in the global business community.

"By 2030, the top 12 [emerging markets] alone will account for 33% of global consumer spending. Annual growth in the average income of poorer groups has outpaced the middle class from the early 1990s," said the BAML team.

They said:

As EM consumers benefit from increasing purchasing power, consumption patterns are expected to move away from basic products and services (i.e. food and clothing). This should drive growth in discretionary industries such as branded apparel, culture, education, healthcare, among many others.

This increase is not only good news for those people moving into the global middle class, but it also presents an opportunity for businesses that make serving these people part of their core strategy.

The note from BAML read:

Such companies provide goods, services and livelihoods on a commercially viable basis, either at scale or scalable, to the Bottom Billions by making them part of the value chain of their core business as suppliers, distributors, retailers or customers.

This spurs innovation, strengthens value chains, builds more effective operations, uncovers new sources of profitability, and enhances long-term competitiveness.

Not only is there good news for the consumers moving into the middle class, but businesses can take advantage and build off of the historic opportunity, too.

All in all, it appears that the growth of the middle class from the rise of the "Bottom Billions" will be among the greatest economic trends of the future.