Copernicus Versus Berkeley Earth – Which Global Temperature is Correct?
Are scientists confused? Some global temperature reports tell us that 2024 is the first year above the 1.5 degrees C above normal dangerous threshold, some say 2023 was, and there are varying reports that say the numerous global temperature evaluations are different from one another.
Part of the challenge is reporting period. Copernicus (the European Weather Service), tells us the 2023 global temperature was 1.498 degrees C above normal, and Berkeley Earth (funded by Lawrence Berkeley National Laboratory and the US Department of Energy among others), tells us the 2023 global temperature was 1.54 degrees C above normal and both have a base period of 1850 to 1900. NASA’s Goddard Institute for Space Studies (NASA GISS) however, has a base period of 1951 to 1980 and a 2023 global temperature of 1.17 degrees C above normal.
Obviously, because considerable warming occurred before 1951, NASA GISS is biased low, relative to a longer base data period. But why is Copernicus at 1.498 C, different from Berkeley Earth at 1.54 C? Berkeley Earth uses more temperature records than the others, so plain and simple, they are quite likely to be more accurate. So why do all of the scientific evaluations of global temperatures not use the same base period and the same thermometer records?
The non-Berkeley Earth temperature evaluations consider some thermometer records to be less robust, say with only a 10 to 30 year record instead of a 100 or more-year record, so they discard this data. Berkeley Earth, for reasons that tell us that the shorter data records are important because most climate change has occurred recently, uses these shorter temperature records for good reason.
Not only are the shorter temperature records much more relative to climate change because most climate change has occurred recently, but they break with established scientific protocols because climate change has broken these protocols. These protocols are that it takes very long time periods to determine with strong statistical robustness what the true average temperature is, because there is so much natural variation in the global temperature from year to year.
So why is NASA GISS at 1.17 degrees C of global warming use a much later baseline of 1951 to 1980 when global warming had already begun? NASA says that this later time period is one that humans that are alive today can more readily relate to because, well they were alive then or much of common knowledge on our weather is based on periods that are more recent.
None of these evaluations are incorrect, but some of them are more meaningful than others. Berkeley Earth using more recent thermometer records even though they lack the robustness of very long time scales, helps us to establish new norms in climate evaluation that reflect where we are today, instead of where we are on average from the last 100 years more or less.
Climate change is new. We have warmed beyond the boundaries of our old climate so the scientific rationale for evaluating our old climate are now different. In the past, when our temperature naturally changed by a a fraction of a tenth of a degree C, higher robustness in statistical method was need to determine “exactly” what the temperature change was. But the maximum temperature of our old climate (with a base period from 1851 to 1900) was at the very most 0.85 degrees C above normal (Hansen 2018). Berkeley Earth says the 2024 global temperature is likely to be about 1.67 degrees C above normal. This is just about double the maximum range of our old climate and far beyond the fraction of a tenth of a degree C change from when our old global temperature evaluation normals were established.
The bottom line is, use Berkeley Earth. Recent changes are important, even if their statistical robustness is weaker than longer temperature records.
The following are summaries of Copernicus and Berkeley Earth’s latest temperature evaluations from October 2024 that contain some fascinating statistics not mentioned above.
Copernicus: 2024 virtually certain to be the warmest year and first year above 1.5°C (Link)
Global Temperatures
- October 2024 was the second-warmest October globally, after October 2023, with an average ERA5 surface air temperature of 15.25°C, 0.80°C above the 1991-2020 average for October.
- October 2024 was 1.65°C above the pre-industrial level and was the 15th month in a 16-month period for which the global-average surface air temperature exceeded 1.5°C above pre-industrial levels.
- The global-average temperature for the past 12 months (November 2023 – October 2024) was 0.74°C above the 1991-2020 average, and an estimated 1.62°C above the 1850-1900 pre-industrial average.
- (Much more at the link above.)
The average global temperature anomaly for the first 10 months of 2024 (January to October) is 0.71°C above the 1991-2020 average, which is the highest on record for this period and 0.16°C warmer than the same period in 2023. It is now virtually certain that 2024 will be the warmest year on record. The average temperature anomaly for the rest of 2024 would have to drop to almost zero for 2024 to not be the warmest year.
Given that 2023 was 1.48°C above the pre-industrial level according to ERA5, it is likewise virtually certain that the annual temperature for 2024 from ERA5 will be more than 1.5°C above the pre-industrial level, and likely that it will be more than 1.55°C above.
Berkeley Earth Temperature Update October 2024
Earth’s temperature in 2024 almost certain to be hottest ever (Link)
The following is a summary of global temperature conditions in Berkeley Earth’s analysis of October 2024.
- Globally, October 2024 was nominally the second warmest October since records began in 1850, though by so small a margin as to be effectively tied with October 2023 as the warmest.
- Both the land and ocean averages were also nominally the second warmest for October, though the land-average was less than the record by a not significant margin.
- Particularly warm conditions were present in parts of Asia, North Africa, North America, South America, the Arctic, the western North Atlantic, and North Pacific.
- We estimate that 24 countries set new national monthly-average records for October.
- A weak La Niña is considered likely to develop before the end of 2024, but is not certain.
- The 12-month moving-average continues to be near record warm at 1.64 ± 0.07 °C (2.95 ± 0.13 °F) above the 1850-1900 average.
2024 is almost certain to be the warmest year on record. - (Much more at the link above.)