How much has the global average temperature risen in the last century?
- (1)3.0° F
- (2)1.8° F
- (3)3.4° F
- (4)2.4° F
Answer
Why
Correct — option (2), 1.8° F.
A rise of 1.8° F is a rise of 1.0° C, because a temperature change of 1° C equals a change of 1.8° F.
The US Global Change Research Program's Climate Science Special Report (2017) states that global annually averaged surface air temperature "has increased by about 1.8°F (1.0°C) over the last 115 years (1901–2016)."
The IPCC reports the same size of warming against an earlier baseline. Its Special Report on Global Warming of 1.5°C (2018) puts human-caused warming at approximately 1.0°C above pre-industrial levels. Its August 2021 report puts 2001–2020 at 0.99 °C above 1850–1900, about 1.8° F.
US agencies give nearby figures on other baselines. NOAA's Climate.gov says 2020 was 1.76° F warmer than the twentieth-century average; NASA's Earth Observatory says the average global temperature has risen by a little more than 1° C (2° F) since 1880.
The idea to remember: roughly 1° C, or 1.8° F, of warming since about 1900.
Why the others are wrong
- (1)3.0° F — 3.0° F is about 1.7° C (our conversion), well above every figure quoted here.
It is even above 1.5° C (2.7° F), the level the IPCC's 2018 special report said global warming is likely to reach between 2030 and 2052 if it continues at the current rate.
- (3)3.4° F — 3.4° F is about 1.9° C (our conversion), nearly twice the warming the IPCC reported.
The IPCC's 2018 report put human-caused warming at approximately 1.0°C above pre-industrial levels, with a likely range of 0.8°C to 1.2°C; 3.4° F lies far beyond the top of that range.
- (4)2.4° F — 2.4° F is about 1.3° C (our conversion). That is above the top of the IPCC's August 2021 likely range for 2011–2020, 1.20 °C, or about 2.2° F.
NOAA's figure for a single year comes near it: 2020 was 2.14° F warmer than the pre-industrial period of 1880–1900. That is one year against an early baseline, and it is still below 2.4° F.
Concept
Global average temperature is the temperature averaged over the whole surface of the planet. Agencies report warming as an anomaly: the difference from a chosen baseline period.
Baselines differ. NASA's Earth Observatory counts from 1880, NOAA also compares with the twentieth-century average, and the IPCC compares with 1850–1900. The same warming therefore appears as slightly different numbers.
A change in temperature converts at 1° C = 1.8° F. Adding 32 applies to a thermometer reading, not to a rise.
RPSC's 2021 syllabus lists "Environmental Issues- Desertification, Deforestation, Climate Change & Global Warming, Ozone Layer Depletion" under Geography of World and India.
2020, the last full year before the exam, was among the warmest measured. NASA says it tied with 2016 as the hottest year since record-keeping began in 1880; NOAA ranks 2020 second-warmest, 0.04° F short of tying 2016.
Warming has sped up. NOAA gives 0.14° F per decade since 1880 but 0.32° F per decade since 1981, and the IPCC's 2018 report said warming is likely to reach 1.5°C between 2030 and 2052 at the current rate.
Key facts
- IPCC SR1.5 (2018): human activities have caused approximately 1.0°C of warming above pre-industrial levels (likely range 0.8°C to 1.2°C).
- IPCC AR6 Working Group I summary (approved August 2021): 2011–2020 global surface temperature was 1.09 °C above 1850–1900.
- NOAA Climate.gov: 2020 was 1.76° F warmer than the twentieth-century average and 2.14° F warmer than 1880–1900.
- NASA Earth Observatory: average global temperature has increased by a little more than 1° C (2° F) since 1880.
- USGCRP Climate Science Special Report (2017): global surface air temperature rose about 1.8°F (1.0°C) over 1901–2016; a change of 1° C equals 1.8° F.
Fahrenheit values for the IPCC figures are our conversions (× 1.8). Each source measures from a different baseline.
Study next
Common traps
- Converting a change: multiply by 1.8 only; adding 32 is for thermometer readings, so 1° C of warming is 1.8° F, not 33.8° F.
- Baselines differ: 'since 1880', 'above 1850–1900' and 'above the 20th-century average' give different numbers for the same warming.
- One year is not the trend: NOAA's 2.14° F compares the single year 2020 with 1880–1900, while the IPCC averages whole decades.
A question can ask for the size of observed global warming in °C or °F, or for the baseline period a figure is measured from.
A question can also convert a warming figure between Celsius and Fahrenheit, or ask which body published an assessment, such as the IPCC.
Related PYQs
Select the incorrect statement from the following :
- (1) El Nino and La Nina are a kind of storm.
- (2) During El Nino, there are fewer phytoplanktons off the coast.
- (3) During La Nina trade winds are stronger than usual.
- (4) El Nino & La Nina are the climate patterns.
Answer(1)
Related climate idea: El Niño and La Niña are climate patterns that NASA and NOAA mention when explaining single warm or cool years. That question asks for the incorrect statement about El Nino and La Nina (RPSC's key: option (1), that they are a kind of storm); this one asks how much the global average temperature has risen.
Practice
- practice — not a real PYQ
A rise of 1.5 °C in global average temperature is equal to a rise of –
- (a)1.5 °F
- (b)2.7 °F
- (c)34.7 °F
- (d)3.0 °F
Answer(2) — a change in temperature converts at × 1.8: 1.5 × 1.8 = 2.7 °F. Option (3) wrongly adds 32, which applies only to readings; option (1) skips the conversion; option (4) simply doubles the number. - practice — not a real PYQ
The IPCC's Special Report on Global Warming of 1.5°C (2018) said that, if warming continues at the current rate, it is likely to reach 1.5°C between –
- (a)2021 and 2025
- (b)2030 and 2052
- (c)2060 and 2080
- (d)2090 and 2100
Answer(2) — the report's Summary for Policymakers says global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate. Options (1), (3) and (4) are not the range the report gives.