How do you respond to skeptics that say "It's been warmer in the past"?

There are many people who are skeptical about global warming. They believe that, in the past, it has been warm and so it is not getting warmer as time goes on. They believe that just because one day in the past was warmer than it currently is, global warming does not exist.

For example, they may remember a winter season where the days or the average date was warmer than the current winter season. However, this does not mean that global warming does not take place. You would need to tell the skeptics that data needs to be taken over long periods of time.