You asked.

What is meant by the term "The Browning of America"? Is it a global warming thing?

A quick scan confirmed what I thought. The Browning of America refers to the population statistics of the USA in relation to people with brown skin no longer being a minority while people of white skin no longer being a majority.

Personally, I think this is a great thing. A lot of the increase in darker skin tones is due to intermarriage between white and brown skinned people. The children tend to be beautiful. There is also a general trend for fewer white children to be born while brown skinned children being born have not declined in numbers.

There are of course implications in politics...