Driving cars releases tons of CO2 into the atmosphere (per car). There are 300 million cars on the road in the States. CO2 is a greenhouse gas that contributes to climate change.
75% of U.S. adults are considered overweight, I would think that walking would first help this problem, as well as be a catalyst to other beneficial habits, including eating less meat and more vegetables, which would further reduce the amount of CO2 released from agriculture, as well as slim people's waistlines.
Ok, but this isn't climate change driven problem. Climate change will keep making this problem harder to manage, but the problem is excessive diversions of water feeding the Great Salt Lake. If climate change were solved tomorrow, this would still be a problem.
I'm not saying we shouldn't be working on climate change, but the solution for this problem must be much sooner and more local than a giant worldwide effort.