Whether or not you believe it's man made, there's no way to disagree that global warming is real. Temperatures are changing, storms are getting bigger, and the weather is generally becoming something of an enemy to humanity. The issue is that, in a lot of people's heads, global warming looks a bit like this picture.
If you just think that global warming means exactly that - everything gets warmer Summer will be fantastic and we won't be as cold in Winter - then it's easy to see why you can't see the issue. In reality, if temperatures get too high, ice caps melt, sea levels rise, and it all goes a bit disaster-movie. You may well one day be able to stand in your garden and cook a steak, so long as you don't mind your garden being on fire whilst you do it.