Which natural phenomenon can cause global temperatures to rise or fall on shorter timescales?

• A. Milankovitch cycles
• B. Industrial emissions
• C. ENSO years
• D. Volcanic eruptions

Answer: (C)

Short-term natural fluctuations in global temperatures are driven by the ENSO cycle. El Niño events warm the central and eastern Pacific, which releases heat to the atmosphere and shifts global weather patterns, raising average surface temperatures for a year or two. La Niña events, with cooler Pacific waters and stronger trade winds, do the opposite and lower global temperatures for a similar period. This interannual variability happens on much shorter timescales than other options: Milankovitch cycles are tens of thousands of years, industrial emissions create a long-term trend, and volcanic eruptions typically cause temporary cooling due to atmospheric aerosols. So ENSO years are the natural phenomenon that can cause global temperatures to rise or fall on shorter timescales.