Cities and region­al author­i­ties play a cru­cial role in dri­ving cli­mate action to lim­it glob­al warm­ing to 1.5°C. Despite their crit­i­cal impor­tance, sig­nif­i­cant obsta­cles in data col­lec­tion and vari­abil­i­ty in imple­men­ta­tion com­pli­cate the assess­ment of their con­tri­bu­tions. This study pro­vides the largest analy­sis of cli­mate efforts across more than 3,000 cities and 170 regions with­in the G20 nations, reveal­ing a notice­able uptick in the adop­tion of medi­um- to long-term emis­sions reduc­tion and net-zero tar­gets post-2020. How­ev­er, over 60% of these sub­na­tion­al enti­ties are fail­ing to meet their cli­mate ambi­tions, with a larg­er per­cent­age not achiev­ing the reduc­tion rates nec­es­sary to align with the 1.5°C goal. These find­ings under­score the press­ing need for enhanced account­abil­i­ty mech­a­nisms for sub­na­tion­al cli­mate actions. Imple­ment­ing stan­dard­ized report­ing and boost­ing trans­paren­cy are piv­otal steps to ensure that local and region­al efforts sub­stan­tive­ly con­tribute to achiev­ing both nation­al and glob­al cli­mate objectives.