xkcd is "A webcomic of romance, sarcasm, math, and language" (xkcd doesn't stand for anything). Sometimes it is very funny. Other times it can be quite informative. This one, from today (June 9, 2014) is in the latter category.
What it is showing is that the difference between the last ice age and our modern average is about the same as the temperature increase that is expected by the year 2100. In other words, we will experience the same amount of warming in a period of 100 years as we have already experienced in the last 20,000 years. Also note, we are already beyond the modern average, so global warming is here and affecting us right now.
Note the last position. That represents as much warming as would have already occurred since the days of a snowball Earth. I wonder how long it will take us to get there and if there will still be people denying anything is going on.