With all due respect, I don't think so. Program lifetime cost of the F-35 Lightning is projected at a whopping 1.5 trillion US$. For the same amount of money, you could bring the renewable energy level to 50% of US electricity consumption (~1 US$/W). Scale effects not even included. Nobody wouldn't even miss the fighter (well, nobody missed it for all the years it was late).

It would be a concentrated effort of just 5 years going all the way at the scale of the Manhattan or Apollo projects, just a question of somebody really wanting to do it. It's just that it's way less sexy.

Uh, citation needed.

Isn't the 1.5 trillion number the total cost projected out to 2070 or so? (with maintenance included)

You can't take the cost of the whole program to 2070 and then state that nobody would miss the program. Not saying that defense budgets aren't up for debate, but your line of reasoning is not convincing.

Would spending $1.5 trillion from now until 2070 (the time horizon for the F-35 expenditures) avert climate change? Or will climate change happen anyway, and the only consequence will have been a reduction in our abilities to fight other countries for dwindling fresh water resources?

Everything is not fine, however. We are currently experiencing the effects of global warming. In the first world we are largely insulated from this but we've seen more frequent severe weather (of the 15 busiest hurricane seasons on record -- with records dating back to the 19th century or so -- 10 have been since 2000). Severe drought and heat have also become more common. We've seen migration patterns of wildlife change and that has lead to impacts on communities that rely on those for their livlihood (native communities for example). We've seen the sea level rise 88mm since 1993. There have been real impacts. Just because we don't feel it in the first world, doesn't mean people haven't been impacted.