To meet an Emergency, as that term is defined in this Charter, the Council may make emergency appropriations from the sources provided in Section 510 of this Charter. To the extent unappropriated revenues are unavailable to meet the Emergency, the Council by law may authorize the issuance of emergency notes, which may be renewed from time to time. Emergency notes and renewals issued pursuant to this section may not be paid later than the last day of the next fiscal year succeeding that in which the emergency appropriation was made.