Excellent question. I think the biggest challenge in the near future will be related to how we adapt to the increasing world’s population (which will increase the demand in resources, transportation, energy, etc) in a sustainable way, with a negligible carbon footprint associated to that growth.
Not only engineers are aware and concerned of this, also politicians, scientists, economists, environmentalists, etc. This is why you have probably heard the word “sustainability” so much in the past few years.
I think the biggest challenge will be providing the basics necessities for our every increasing population ( food , clothing, shelter and energy etc). And similar to what Andres said the challenge will be to do this in a sustainable way.
So we need everyone to work together and develop new resources and technologies to make sure we have enough for the generations to come.
I think finding ways of dealing with the worlds increasing population and also climate change at the same time. This is going to pressures on us from two directions and require some ingenuity to get us out of the problems.