expressing opinion

Asking someone for their opinion about an environmental problem
What do you think we should do about ...?
What do you think the government ought to do about ...?

Expressing your opinion politely
Personally, I think that...
Personally, I feel that....
Personally, I believe that...
In my opinion, ...

Politely disagreeing
I can your point, but ...
I see what you mean, but ...
I understand what you're saying, but on the other hand ...

example dialogue

A: What do you think we should do about global warming?
B: In my opinion, the government should pass a law to limit car travel. If they did that, the level of carbon dioxide in the air would decrease.
A: I can see your point, but if we limit car travel, it'll take people longer to get from A to B. That will reduce productivity, because people will spend less time working and more time traveling. And if productivity goes down, there'll be less money available for the government to combat global warming.
B: I don't think that's a very good argument, because money is not the real problem in this case. It's political will-power. We know what we need to do, but we're too lazy to do it.
A: I don't think it's that simple. There's no easy solution to the problem.

by : http://www.angelfire.com/planet/atsuginishihs/F47.html