Eight drastic policy measures necessary to prevent global economic collapse. None of them will be popular.

Because these options cannot work, the sole alternative is an exit from the Eurozone by Greece and some other current members. Only a return to a national currency—and a sharp depreciation of that currency—can restore competitiveness and growth.

Leaving the common currency would, of course, threaten collateral damage for the exiting country and raise the risk of contagion for other weak Eurozone members. The balance-sheet effects on euro debts caused by the depreciation of the new national currency would thus have to be handled through an orderly and negotiated conversion of euro liabilities into the new national currencies. Appropriate use of official resources, including for recapitalization of Eurozone banks, would be needed to limit collateral damage and contagion.

Seventh, the reasons for advanced economies' high unemployment and anemic growth are structural, including the rise of competitive emerging markets. The appropriate response to such massive changes is not protectionism. Instead, the advanced economies need a medium-term plan to restore competitiveness and jobs via massive new investments in high-quality education, job training and human-capital improvements, infrastructure, and alternative/renewable energy. Only such a program can provide workers in advanced economies with the tools needed to compete globally.

Eighth, emerging-market economies have more policy tools left than advanced economies do, and they should ease monetary and fiscal policy. The International Monetary Fund and the World Bank can serve as lender of last resort to emerging markets at risk of losing market access, conditional on appropriate policy reforms. And countries like China that rely excessively on net exports for growth should accelerate reforms, including more rapid currency appreciation, in order to boost domestic demand and consumption.

The risks ahead are not just of a mild double-dip recession, but of a severe contraction that could turn into the Great Depression II, especially if the Eurozone crisis becomes disorderly and leads to a global financial meltdown. Wrong-headed policies during the first Great Depression led to trade and currency wars, disorderly debt defaults, deflation, rising income and wealth inequality, poverty, desperation, and social and political instability that eventually led to the rise of authoritarian regimes and World War II. The best way to avoid the risk of repeating such a sequence is bold and aggressive global policy action now.

Read this story at Project Syndicate.