Electricity from solar photovoltaic generation has life cycle emissions 90-95% lower than fossil-derived electricity, per median figures in the IPCC's 2014 tabulation of global warming potential of selected electricity sources. Geothermal, concentrated solar power, nuclear power, and wind power have even lower life cycle emissions.
https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...
Displacing fossil-derived electricity with enough low-carbon electricity to supply an air conditioner is more effective than raising the AC temperature one degree or planting a tree.
The key issue is to reduce emissions. Sometimes that necessitates reduced consumption of energy services [1]. But reducing consumption is not sufficient and often not necessary to deeply cut emissions.
If 3 tons of CO2 per capita per year is a sustainable emissions rate, then the US emits at about 550% of the sustainable rate. Even Cuba emits at 107% of the sustainable rate. No polity is going to voluntarily reduce their material standard of living below that of Cuba. And even a super-emitter like the US could reach the sustainable rate with a combination of more efficient energy use and non-fossil (renewable and nuclear) primary energy production substituting for fossils. So I think that "stop burning fossils for air conditioning" is a prescription closer to solving the root problem than "endure a little more discomfort in the air conditioning season."
[1] For example, there is no foreseeable technology that will enable trans-Atlantic passenger flights without burning chemical fuels. Long distance flights could burn synthetic fuels made using non-fossil electricity, but that would raise fuel prices. Whether by fiat or by pricing, long distance air travel will necessarily become less common if/when aviation faces pressure to reduce CO2 emissions.