Recent warming in context: magnitude, pace and reliability of data

How large and how fast?

• Global surface temperature was 1.09 C (range 0.95 to 1.20 C) higher in 2011 to 2020 than in 1850 to 1900 (IPCC AR6, 2023).
• In 2019, atmospheric CO2 (410 ppm) was higher than at any time in at least 2 million years (IPCC).
• NOAA states that the late 20th and early 21st centuries are likely the warmest period in at least 1,200 years; the Medieval Warm Period was comparable only with early 20th century temperatures in the Northern Hemisphere.
• Pace: natural glacial-interglacial changes happened over thousands of years; the recent rise has taken place mostly since about 1960, over decades.

Reliability, coverage and accuracy

• Past data are reconstructed from proxies, which carry uncertainty and must be calibrated; they cover some places (polar ice, temperate forests) better than others.
• Early instrumental records (from about 1850) are sparse over oceans, the Southern Hemisphere, Africa and the poles; instruments and observing times changed; some stations were affected by growing cities (the urban heat island).
• Recent data are better: global networks of stations, ocean buoys and satellites.
• Predictions depend on models and on assumptions about future emissions, so they are given as ranges.

In the exam, questions often ask you to compare two periods on a graph: make an explicit comparison (for example below average before 1980, above average after) rather than describing the whole trend.

Worked example

Using IPCC AR6, estimate the average warming rate per century between the mid-points of 1850 to 1900 and 2011 to 2020.

1. Mid-points: 1875 and 2015.5, so about 140.5 years apart.
2. Rate = 1.09 C / 1.405 centuries

Answer: About 0.78 C per century on average, with most of it since 1960.

Check yourself

1. Warming of 1.09 C occurred between the mid-points of 1850 to 1900 (1875) and 2011 to 2020 (2015.5). Calculate the average rate in C per century, to 2 decimal places.
   Show answer

   0.78. 1.09 / 1.405 = 0.78 C per century.

2. What is the IPCC AR6 best estimate of warming in 2011 to 2020 compared with 1850 to 1900?
   • 0.2 C
   • 1.09 C
   • 4.4 C
   • 2.7 C
   Show answer

   1.09 C. 1.09 C with a range of 0.95 to 1.20 C.

3. Why are global temperature records from the 1850s less reliable than recent ones?
   • Thermometers did not exist
   • The climate did not change then
   • Satellites gave false readings
   • Few measurements were made over the oceans, Southern Hemisphere and poles
   Show answer

   Few measurements were made over the oceans, Southern Hemisphere and poles. Coverage was sparse before modern networks.

4. Why can a weather station in a growing city give misleading long-term trends?
   • The urban heat island warms the site as the city grows
   • Cities have no weather
   • Rainfall cools the instruments
   • Cities are always at high altitude
   Show answer

   The urban heat island warms the site as the city grows. Local urban warming can be mistaken for global warming unless corrected.

5. Which statement best compares recent warming with past natural change?
   • It is slower than glacial terminations
   • It is the same as the Medieval Warm Period
   • It is much faster, taking decades rather than thousands of years
   • It has the same cause as the Little Ice Age
   Show answer

   It is much faster, taking decades rather than thousands of years. The pace is unusual, as well as the CO2 level.

6. A graph shows global temperature anomalies from 1880 to 2020. Explain what a good answer to 'Compare temperatures before and after 1980' must include.
   Show answer

   It must make a direct comparison of the two periods, for example temperatures were mostly below average before 1980 but above average after 1980, rather than describing the whole trend.. Comparative statements about the two periods, with data.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• IPCC AR6 Synthesis Report: Summary for Policymakers (2023)
• NOAA Paleoclimatology (archived): The Medieval Warm Period
• Pearson principal examiner report, WGE01 Global Challenges, June 2025
• Pearson WGE01 mark scheme, June 2025 (copy hosted by Physics and Maths Tutor)

Last updated 8 November 2026. Spotted a mistake? Tell us.