二者的用法都是正确的，但是侧重点不同：

environment，指的是你生活中环绕你周边的人、事、物或者某个地方的大自然属性（气候、土壤、植物种类等等）。所以environment change 往往是指用某种environment去替代（to replace）另外一种environment，也就是乐乐老师说的“环境本身的变化”；

environmental，意思是与environment相关，所以environmental change 往往是指这种改变只是与environment相关（related）而已；

回到网友问题，当我们说“环境问题”的时候，往往是泛指一切与环境相关的问题，所以用environmental problems用得比较多（比如上例提到的various types...different kinds）。用environment problems的也有，不过这时候，往往是指某类/某种具体的环境问题。

一家之言，仅供参考；勤查英英，必有所获！

我更认同凡哥老师的解答：网友的这两个例子的两种用都对，只能说其中一种用法更普遍，如environmental problems 更普遍。但有些又是不能替换的，属于习惯用法，如：car rental service, 一般不说car rent service. 又如： doctor's degree,或doctoral degree, doctorate, 但没见过doctor degree. 其实学语言，比较稳妥的办法是用你见过的，没把握尽量不去替换。很多网友喜欢“公式化”思维来学英语，这的确是聪明的表现，但有时这种“聪明”反被聪明误，因为对学外语的人来说，语言中有很多你看不出的陷阱。我再提供几个外媒例句供参考：

environment problem

The client was assisted with identifying several ways in which living environment problems have had a negative impact on his/her recovery.

This study should not create the misunderstanding that we would advocate solvt ing all our environment problems through international cooperation.

The demand for information and involvement in social, economic and environment problems was rapidly growing.

environmental change:

The study of environmental change is a major growth area of interdisciplinary science.

Global climate and environmental change is one of the key scientific and societal issues worldwide.