I think you can argue this one either way. If you want to be optimistic and say we are heavily involved in "going green", you could argue the point that we have seen the error of our ways and are doing the things that reduce our damage to the environment we live in. On the other hand, if you have no faith in our promise to do better, that we will continue to do what we have done these past 100 to 150 years to promote levels of carbon dioxide, you could write a very persuasive argument to the negative that things will change, but for the worse.
I think you can also take an optimistic perspective on this. You could say that we are working to stop pollution, and we will reduce the use of fossil fuels and accompanying pollution. In that case, the air will get cleaner and there will be less pollution than now.
Your question is supposed to combine the scientific belief that our environment is changing dramatically and very quickly and put these ideas in essay form. That means that first, you must decide what your view is of this statement. Do YOU believe the environment is changing now and then think ahead for 50 years of change. If you believe this, your thesis statement should reflect your belief. An example might be, "In my opinion, our environment will change dramatically because of many environmental pressures which exist today." Then you can decide if you want to use atmospheric pollution CAUSED BY WHAT, water pollution CAUSED BY WHAT and the constant decrease in the ozone layer which is CAUSING WHAT TO HAPPEN. You have plenty of material available because pollution and global warming are hot topics. Be sure to be specific and use examples to prove what you say which prove your thesis. With your conclusion, you might want to suggest what people who read your essay might do to help the situation now.