I feel the remark was inappropriate for such a serious issue.

我觉得对如此严肃的问题来说，这评论是不恰当的。

There is one serious issue, however.

然而，这里有一个严重问题。

It is a serious issue.

这是一个严重的问题。

Global warming is a serious issue.

全球变暖是很严重的问题。

Obviously, this is a far more serious issue.

而显然，这次的问题更为严重。