A new World Bank report projects that tens to hundreds of millions of people fleeing the gradual effects of climate change will shift centers of population within many countries in Latin America, South Asia and sub-Saharan Africa. If emissions of greenhouse gases remain high, as many as 143 million “internal migrants” might move within their own countries, comprising as much as 3.5 percent of the total population of the studied regions by 2050, according to the report. It says such movements could accelerate after 2050.