The International Monetary Fund this week released its updated estimate of losses to the world's financial sector. The new figure, $4,050bn globally, does not come as a surprise. It is nonetheless shocking.

For more than a year, the IMF's loss estimate has swollen with each update. As late as October, it expected losses on US loans and securities of $1,400bn; it now foresees losses almost twice that size, at $2,700bn. In addition, it has now added forecast losses of $1,200bn in Europe and $150bn in Japan.

The ballooning numbers reflect two important facts. We have no certainty whatsoever as to what the real losses will eventually be – except that they get worse every time we look. Last year's gloomiest forecasts have proved far too optimistic.