Complex sentence: Kista Science Tower was completed in 2003 and was then the tallest building in Scandinavia, but was surpassed by Turning Torso, built in Malmö in 2004.
Split into simpler sentences: Kista Science Tower was completed in 2003. It was the tallest building in Scandinavia at the time but was soon surpassed by Turning Torso, built in Malmö in 2004.