According to an article by Reuters Science, the Next Ice Age is not likely to occur for another 1500 years.
High levels of carbon dioxide in our atmosphere is why a probable ice age would be delayed. Gases were measured to study the effects of global warming from 2010 to the present that show that even if we stopped emitting these gases we would have enough in the air to affect us for decades to come. About 20 % of C02 may stay in the atmosphere for thousands of years. Some carbon dioxide is produced by humans and animals, but the prime concern is the high levels as a result of burning gas, oil and coal. I read a scary statistic showing that to bring the Earth's atmosphere to pre-industrial levels, we would need to remove 70% of the existing C02!
I also wish to credit wikipedia for some alarming data and background information.