I don't know how software can be used to fix any of the "big" problems other than as an avenue for information and manipulation through social media.
Like for example we know that if we want to do anything about climate change we probably need to change our diets. I don't know how we can convince anyone to do that except through questionable means like social media campaigns.
Software is good at one thing processing information. Anything you can do to improve information about environmental damage of products helps.
For example CO2 emissions of vehicles are published. But not the CO2 cost of making the vehicle. People buying new cars don't know what the CO2 impact of a new car is, at the point of sale. If you can use software to get that information in front of consumers, it helps people make the right choices.
If people don't make the right choices with good information, use the information gathered to proportionally tax the products because even selfish consumers can read the price tag.
Software may not cause a change in diet, but machine learning and software stacks are being employed to help boast yields on agricultural output. It may not change peoples diets, but if it helps farmers who grow cops know when is best to water, fertilize or know the weather to plan their activities and results in better quality and quantity yields, it is going to have an impact.
Like for example we know that if we want to do anything about climate change we probably need to change our diets. I don't know how we can convince anyone to do that except through questionable means like social media campaigns.