Paris

IT has been three years since the collapse of Lehman Brothers and the start of a financial crisis that still casts a dark cloud over the global economy.

Governments, both rich and poor, urgently need a way to calm speculation in the financial markets and to raise revenue. On Wednesday, the European Commission president, José Manuel Barroso, proposed a tax on financial transactions. Such a measure, already supported by the German chancellor, Angela Merkel, and the French president, Nicolas Sarkozy, is long overdue.

Indeed, a tax of just 0.05 percent levied on each stock, bond, derivative or currency transaction would be aimed at financial institutions’ casino-style trading, which helped precipitate the economic crisis. Because these markets are so vast, the tax could raise hundreds of billions of dollars a year globally for cash-strapped governments and could increase development aid.

The global economic storm may have sprung from the high-pressure trading rooms and overheating economies of developed countries, but its effects have also been felt far away. Any additional revenue raised by a financial transaction tax should therefore be devoted not only to shoring up slumping economies in rich nations but also to helping the world’s poorest countries.