IB ESS HL 2.4.10 ENSO Cycle Question Bank
Explain El Niño–Southern Oscillation and its effects on climate and ecosystems.
- Syllabus
- First assessment 2026
- Course
- ESS HL
- Level
- HL
Exam points
- identify the climate mechanism or pattern
- trace the atmospheric or oceanic process
- evaluate impacts and uncertainty using evidence
2.4.10 (HL)—ENSO cycle question 1
Question (a)
(a)
Figure:Eastern Pacific subsurface sea temperature deviations, 1950-2011
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Question (i)
(i)
Using Figure: Eastern Pacific subsurface sea temperature deviations, 1950-2011, calculate the average frequency of El Niño events between 1990 and 2010.
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Question (ii)
(ii)
Figure:El Nino and La Nina events
- Figure: El Nino and La Nina events: El Nino and La Nina are changes to normal wind patterns in the southern Pacific that affect climate worldwide.
- In El Nino years winds do not blow east to west across the Pacific, causing excess rainfall on the South American coast and droughts in Australia and Indonesia.
- La Nina events follow strong El Nino events; eastern Pacific ocean temperature is unusually cold after being unusually hot.
Figure:Effects of the 2010-2011 La Nina event
Figure: Effects of the 2010-2011 La Nina event: the 2010-2011 La Nina was one of the strongest ever recorded.
Linked impacts included flooding in Queensland and Sri Lanka, winter storms in North America, and deadly mudslides near Rio de Janeiro.
Suggest two reasons why both El Niño and La Niña events may be having a greater impact on human populations today than in the past.
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