>>142 を少し変えた次のような構文だと僕は思う。変えた部分に「★　★」の印をつけておく。

S= tackling climate change
V= entails ★achieving★
O1= zero net carbon emissions by 2100
O2= an economy (that is taking carbon out of the atmosphere,
rather than adding to it, in the second half of this century.)