I was going to say "It's an endless fight", but it isn't true. The fight will end when we all die. The horrors that are coming are unspeakable. During the famines in Russia during the civil-war starving mothers ate their children. Famine is our future. In the USA, we are already locking up climate refugees, many children, in cages.
Things are already starting to get bad and we aren't at 1.5C, or 2C, or the 3-4C we are projected to hit by end of the century.
Funnily enough, I think this would actually be justified if climate change was going to cause imminent famine as you're suggesting. Given the choice between having the population of the US undergo a mild famine while to the south there's a famine beyond living memory (thanks to preventing climate-motivated migration) or having a famine beyond living memory here (thanks to the extra few hundred million mouths to feed), I know which one I would want the US government to choose. Helping refugees is a good thing, but the US government has an obligation to US citizens first and foremost. That's why we call it the United States government, and not the Mexican government, or Guatemalan government, or Honduran...
If you let too many people get into the lifeboat, you all drown.
I don't think that this is currently the case, though. Famine, when it comes, will affect the rest of the world far more than it will the US, Canada, and Russia. Food will become more expensive, but that will be due to exports rather than having more people than the land can feed - unlike almost every other country on the planet. Also barring further improvements in agriculture, of course.
USA has had the biggest impact on climate in the last 100 years and is responsible for the bulk of climate emissions. In other words, the rest of the world will starve because of us and somehow we can justify building walls to protect ourselves. If there is a thing as "evil" it most certainly is that.
I think that when it comes to total impact on the ability of the rest of the world to feed itself, the US is probably pretty far in the black. Yes the contribution to climate change is negative, but the Green Revolution  is almost certainly very, very positive. Improved agricultural tech, including GMO crops, have fed a lot of people around the world.