Use carbon capture to generate fuel from the air. Yes it's expensive compared to regular diesel, but for use-cases with low consumption like emergency generators that really shouldn't be a huge issue.
Using fossil fuels is saving more lives, in fact it's making it possible for billions of people to live today. That wouldn't be possible without fossil fuels. In fact most of us wouldn't be here.
There's pretty clear scientific consensus that climate change will result in more hurricanes, wildfires, heat waves, cold spells, floods, droughts and especially that there will be shortages of clean water and land suitable for agriculture. All of those things kill humans.
And everyone, everything would be better off.
Besides, the cost could be born by others similar to how we have duty-free fuel here for farm equipment and similar.