El Niño and La Niña are natural climate phenomena that alter weather patterns around the world. El Niño occurs irregularly but shows up roughly every three to seven years and typically lasts between nine and 12 months with occasional exceptions that linger for multiple years.

El Niño’s effects are powerful. Its ocean warming is enough to drive average global temperatures higher, and to temporarily raise sea levels along the California coast via thermal expansion – offering humanity a glimpse of conditions that are projected to become the norm in coming decades as climate change accelerates.

To learn more, we asked experts from UC San Diego’s Scripps Institution of Oceanography to answer some common questions about El Niño and its impacts.