More than two dozen of the world’s largest cities are no longer increasing their planet-warming greenhouse gas emissions, they announced at a global climate summit in San Francisco.

S More than two dozen どんな→[of] the world’s largest cities
V [are no longer increasing] 増やしていない
O their planet-warming greenhouse gas emissions 温室効果ガス
,

S they
V [announced]

補足
[at] a global climate summit サミット
[in] San Francisco.