El Niño, Sunspots or CO₂? Questions From the Weather Club

Use ocean-pattern and Sun-cycle data to ask sharper questions about global warming.

Answer Key

A record year and the Pacific Ocean

Read the passage and Table A, then answer the questions.

The Record That Started the Questions

1The weather club at Harrow Hill Middle School runs a rooftop weather station that measures air temperature, humidity, wind and rain. Its readings feed a forecast app that students and teachers check every morning. The station has been running since 2012. In January 2025, the app reported that 2024 had been the warmest year at the school since the station was set up. It also reported that 2024 was the warmest year on record for Earth as a whole. Club adviser Mr. Lorenzo Gatti asked members Sakura Endo and Darius Mensah to prepare questions for a video call with a climate scientist about what has caused Earth's temperature to rise over the past century.

2Darius learned that 2024 was also an El Niño year. El Niño is a pattern in which the surface water of the eastern tropical Pacific Ocean becomes warmer than usual for several months. During El Niño, the ocean gives off extra energy to the air, so the planet as a whole tends to be warmer than in the years around it. La Niña, the opposite pattern, brings cooler-than-usual water to the same area and tends to make a year a little cooler. The two patterns come and go every few years.

3Sakura looked into the Sun. The energy the Sun gives off rises and falls slightly in a cycle that lasts about 11 years. At solar maximum, the Sun has many sunspots and sends out a little more energy; at solar minimum, it sends out a little less. Satellites measure the energy arriving at the top of Earth's air.

4Mr. Gatti added that greenhouse gases, such as carbon dioxide (CO₂), absorb energy given off by Earth's surface and send some of it back down. Burning coal, oil and natural gas adds CO₂ to the air. He also explained one way scientists tell these factors apart. Extra energy from the Sun would warm the whole atmosphere, from the ground up to the thin, high layer called the stratosphere. Extra greenhouse gases trap energy in the lower air, and the stratosphere tends to cool.

5The global data in the tables are based on real measurements, rounded. Temp change means how much warmer the year was than the average for 1951–1980.

Table A. Global Temperature in El Niño and La Niña Years
Year	Pacific pattern	Temp change (°C)
1983	El Niño	0.3
1989	La Niña	0.3
1998	El Niño	0.6
2000	La Niña	0.4
2011	La Niña	0.6
2016	El Niño	1
2022	La Niña	0.9
2024	El Niño	1.3

Use Table A.

The 2016 El Niño year was 0.4 °C warmer than the 1998 El Niño year. The 2022 La Niña year was 0.3 °C warmer than the 1998 El Niño year.

Which statement best describes Table A?

A. Both kinds of years grew warmer over time, and recent La Niña years beat older El Niño years.
B. Earth warmed in El Niño years and cooled back to about 0.3 °C in La Niña years.
C. The El Niño years grew warmer over time, but the La Niña years stayed at about 0.3 °C.
D. La Niña years were warmer than the El Niño years that came just before them.

Darius wonders whether El Niño could be the cause of the long-term warming. Which question would best test his idea?

A. Was the water off South America warmer in 2024 than in 2023?
B. Which countries got the heaviest rain during the 2016 El Niño?
C. How many months did the 2024 El Niño last in the Pacific Ocean?
D. Have El Niño years become more common or stronger since 1950?

Use paragraph 1. Underline each question that the club's own rooftop station could help answer.

Was 2024 warmer at the school than 2023?Has Earth's average temperature risen since 1900?Did more rain fall on the school in 2024 than in 2022?Has the CO₂ in Earth's air increased since 1950?Did the Sun send out less energy in 2019 than in 2014?Is the roof usually windier in the afternoon than at dawn?

The Sun's cycle and CO₂

Use Table B and the passage.

Table B. The Sun's Cycle, CO₂ and Global Temperature
Year	Sun cycle	Sunlight (W/m²)	CO₂ in air (ppm)	Temp change (°C)
1990	Maximum	1361.4	354	0.5
1996	Minimum	1360.6	363	0.3
2001	Maximum	1361.4	371	0.5
2008	Minimum	1360.5	386	0.5
2014	Maximum	1361	398	0.8
2019	Minimum	1360.5	411	1

Sunlight = the average energy from the Sun arriving at the top of Earth's air that year, in watts per square meter (W/m²). ppm = parts per million (how many CO₂ molecules there are in every million molecules of air).

Compare the 1990 solar maximum with the 2014 solar maximum. Do not round.

Sunlight in 2014 was 0.4 W/m² lower than in 1990, but the temp change value was 0.3 °C higher.

Which conclusion about the Sun does Table B support best?

A. The temperature dropped at each solar minimum, so the Sun's cycle explains the long-term rise.
B. Sunlight fell by more than 1 W/m² in each cycle, so the planet has been slowly cooling.
C. Sunlight rose and fell with the cycle without climbing overall, while the temperature kept rising.
D. Each solar maximum was brighter than the one before, which explains the rise in temperature.

Use paragraph 4. Which question would best help scientists tell whether the Sun or greenhouse gases caused most of the warming?

A. Has the stratosphere warmed or cooled while the lower air warmed?
B. How many sunspots could be seen on the Sun during 2024?
C. How many years does each of the Sun's cycles usually last?
D. Is sunlight at noon stronger at the equator than at the poles?

Club members heard four claims at a school assembly. Match each claim to the question that would best test it.

"Cutting down forests adds to the warming."C
"The Sun is getting brighter."A
"Our station reads warm because of the new parking lot."B
"Burning fuel is warming Earth."D

A. Has sunlight at each solar maximum gone up since 1980?
B. Did the station's readings jump after the lot was paved?
C. How much CO₂ has clearing forests released each decade?
D. Has the CO₂ from burning fuel risen as temperatures rose?

The app says 2024 was the school's warmest year since 2012. Sakura wants to know whether her town has warmed along with the rest of the planet. Which question would help her most?

A. How warm does the forecast app say next summer will be?
B. How has the town's average temperature changed over 100 years of older records?
C. Was 2024 warmer than 2023 at the airport across town?
D. Which month of 2024 was the warmest one on the school roof?

10.

Darius's cousin says, "The 2024 record was just El Niño plus a strong Sun. Earth isn't really warming over the long term." Do you agree? Write a claim, use data from both tables, and explain your reasoning. Then write one new testable question you would ask the climate scientist, and name the data that would answer it.

Claim: I disagree. El Niño and the Sun cause small ups and downs, but Earth has also warmed over the long term, and rising CO₂ is a more likely cause. Evidence: In Table A, the 2022 La Niña year (0.9 °C) was warmer than the 1998 El Niño year (0.6 °C), so even the cooler kind of year is warmer now than the warm kind of year was before. In Table B, sunlight at the 2014 solar maximum (1361.0 W/m²) was lower than at the 1990 maximum (1361.4 W/m²), yet the temperature change rose from 0.5 °C to 0.8 °C. Over the same years, CO₂ rose from 354 ppm to 411 ppm. Reasoning: If El Niño and the Sun were the only causes, temperatures would go up and down with them and not keep climbing. The Sun's energy did not rise while Earth warmed, but CO₂, a greenhouse gas, rose along with the temperature. New question: Has the stratosphere cooled while the air near the ground warmed since 1980? Temperature measurements from weather balloons and satellites at different heights would answer it.