Alibaba founder Jack Ma was world's top earner in 2014

The world's 400 richest people added some US$92 billion to their collective wealth in 2014, according to the Bloomberg Billionaires Index - as of December 29, they were worth a combined US$4.1 trillion.

The year's biggest climber was Jack Ma Yun, the co-founder of Alibaba, China's largest e-commerce company, who added US$25.1 billion to his fortune after Alibaba's initial public offering in September.

Microsoft's Bill Gates remains the world's richest man, adding about US$9 billion to his net worth, which is now valued at US$87.6 billion.

In a year of geopolitical instability, not all the mega rich were so lucky. A clutch of influential Russian billionaires suffered as a result of sliding oil prices and Western sanctions on Moscow. Alisher Usmanov, who entered 2014 as Russia's richest man, lost a third of his wealth.

In any event, these eye-popping figures should not be a surprise. Global inequality is deepening, with millions of poorer people around the world affected by rising rates of joblessness and decreasing incomes. At the same time, the world's population of billionaires is growing.

Concern about the yawning gap between the world's rich and poor fuelled the astonishing success of French economist Thomas Piketty's book Capital in the Twenty-First Century, whose English edition was published last year. He proposes, among other things, a global tax on capital to force the world's billionaires to pay a fairer share.