Berlin's recent sovereign green bond issue is a gauge of strong investor interest in climate-friendly debt. Berlin knocked it out of the ballpark with its latest sovereign green bond issue, which sparked strong demand for climate-friendly debt even as the bond market as a whole was experiencing a selloff and demonstrated a clear greenium — ie. cheaper financing for green projects. The latest green Bund issue of €6 billion ($7.25 billion) in the last week of April — Germany’s first 30-year green sovereign bond — was oversubscribed by more than…