Passage: Cole released his debut studio album, Cole World: The Sideline Story, in 2011. It debuted at number one on the U.S. Billboard 200, and was soon certified platinum by the Recording Industry Association of America (RIAA). His next two releases, 2013's Born Sinner and 2014's 2014 Forest Hills Drive, received mostly positive reviews from critics, and both were certified platinum in the United States. The latter earned him his first Grammy Award nomination for Best Rap Album. In December 2016, Cole released his fourth studio album 4 Your Eyez Only. The album debuted at number one on the Billboard 200 chart and was certified platinum in April 2017. His fifth album, KOD, was released in April 2018. The album debuted atop the Billboard 200, making it his fifth album to reach number one on the chart.

Question: Cole's debut album was released in what year?
2011