No one thing is going to save Earth. Humans have to stop using fossil fuels completely and use farming methods that return massive amounts of carbon to the soil. Non till farming and adding biochar to the soil in huge amounts will help. We will also have to reduce the population drastically. All of this might do it, but we will pass a point of no return soon and nothing will stop the Venus syndrome.

Many plants contain protein.
As peas are a sustainable crop, have protein and taste good, I will eat them.

I have been growing and eating field peas for most of my life. They are delicious. They are easy to grow -- given heat and moisture, they grow like weeds. They add nitrogen to the soil, like all legumes. I grew up with acre peas and brown crowder peas in Florida and Georgia. I had acre pea seeds sent to me when I lived in Kansas, and in the Kansas summer heat they produced like crazy. I am sure that they would do well anywhere in the South or Midwest.