The global recession that followed the financial crisis was the most severe in half a century, an unusually synchronized shock that paralyzed trade and left 23 million more people out of work.

Yet the response by policy makers hasn’t been up to the task, with central banks bearing too much of the burden. And the world may be on the edge of another recession, even though it hasn’t recovered from the last one.

Those are the conclusions of a new book on business cycles released Tuesday by the International Monetary Fund.

“The 2009 episode was the most severe of the four global recessions of the past half century and the only one during which world output contracted outright -- truly deserving of the ‘Great Recession’ label,” write Ayhan Kose, director of the World Bank’s Development Prospects Group, and Marco Terrones, deputy division chief at the IMF’s research department.

“The possibility of another global recession lingers in light of the persistently weak recovery, even though damage from the previous one has yet to be fully repaired.”

The 272-page book, “Collapse and Revival: Understanding Global Recessions and Recoveries,” underscores the challenges policy makers face as they try to jumpstart a sputtering recovery more than six years after the global financial crisis.

A slowdown in emerging markets driven by weak commodity prices forced the IMF this month to cut its outlook for global growth in 2015 to 3.1 percent, which would be the weakest rate since 2009, from a July forecast of 3.3 percent.

Kose and Terrones try to answer a question that has become more pressing as nations become more integrated: How do you define a global recession? For individual countries, the rule of thumb is two consecutive quarters of falling output. That convention is difficult to apply to the world economy, which rarely contracts. 

Citigroup Forecast

In predicting a global recession next year, Citigroup Inc. Chief Economist Willem Buiter recently forecast that world growth would slow to “well below” 2 percent in 2016.