What effect will these changes in population have on the environment and economy of Brazil?

I think the population change will surely have an impact on the environment as well as the economy.

As the population increases, there would be more demand for resources which will directly affect the environment such as more land would be required for housing. And that land will come from the existing vegetated area, thus decreasing the vegetation cover. The urban areas might increase as well with more urbanization. 

On the economic front, the standard of living might improve with the government investing more as the population increases. The government might have to spend more for the older population such as for retirement funds, considering that in the long term their size will increase. I think the working force will be the same, more or less.