Over the past 20 years, vast swaths of the world's oceans have changed color, turning a soft green toward the tropics, researchers say, highlighting the impact of climate change on life in the world's oceans. In new research published Wednesday, scientists said they have recorded color shifts across more than half of the world's oceans — an area larger than the entire land area of Earth. The authors of the study in the journal Nature believe that changes in ecosystems, and in particular tiny plankton, which are central to the marine food web and play a key role in stabilizing our atmosphere, are to blame.