A new study in the journal Science says the planet is becoming the hottest it has ever been in the last 11,000 years.
Researchers used fossils and other pieces of data from around the world to reconstruct global temperatures since the end of the last Ice Age.
They conclude that the Earth was cooling significantly before a spike in global temperatures after 1910. And they say the last decade was one of the hottest on record.
Some scientists say human activity and pollution from cars and factories is causing the Earth to warm up. Others say natural forces are causing global warming.