In an open letter to the German leader published online by the US magazine The Nation, they said that Greece had already complied with its creditors' push for austerity, with the result only a deep economic depression.
"The medicine prescribed by the German Finance Ministry and Brussels has bled the patient, not cured the disease," they said.
With Merkel seen now as the key to whether official creditors will bend to Athens's call for easier bailout terms, the writers called on them "to consider a course correction, to avoid further disaster and enable Greece to remain in the eurozone."
Specifically they said the country needs "a major reduction" of its debt, to accompany reforms being asked of Athens.
With only reform demands and no debt relief being offered Greece, they said: "Right now, the Greek government is being asked to put a gun to its head and pull the trigger."
"Sadly, the bullet will not only kill off Greece's future in Europe. The collateral damage will kill the eurozone as a beacon of hope, democracy and prosperity."
"To Chancellor Merkel our message is clear; we urge you to take this vital action of leadership for Greece and Germany, and also for the world. History will remember you for your actions this week."
The letter was signed by Piketty, the French economist known for his work on income disparity; Columbia University development economist Sachs; Harvard political economist Dani Rodrik; Simon Wren-Lewis, an Oxford University
economist; and Heiner Flassbeck, former state secretary in the German finance ministry.
German Red Cross ready to provide aid
The German Red Cross said Wednesday it was willing to rush medical and other humanitarian aid to Greece as the country's economy teetered on the brink of collapse.
"We are ready in every respect," German Red Cross spokesman Dieter Schutz said in an interview with the Leipziger Volkszeitung newspaper.
"Pensioners, the poor, the sick and refugees" have been hit hardest, he said.
"There are already problems with medical care," he added, in an apparent reference to stocks of drugs.
The German government is seen as Greece's most stubborn opponent in negotiations over how to tackle the financial crisis, refusing to allow a restructuring of Greek debt without reforms.
German Economy Minister Sigmar Gabriel said Monday that an emergency eurozone meeting Tuesday should discuss humanitarian aid for Greece, where banks have been closed since June 28 amid fears of an imminent collapse of the