The Paris Agreement talks about staying under 1.5°C and 2°C of global warming above the “Pre-Industrial” baseline. As per Baseline Adjustment Examples, people often show graphs with a different baseline (E.g. 1991-2020). This page provides conversion tables, so you can quickly add an adjustment to convert the Y-Axis to get pre-industrial values were calculated and verified. See Baseline Adjustment Evidence to see how the adjustment values. As per About, these are “best efforts”, and I will update them (see Errata) if necessary.
Quick and Dirty Baseline Adjustments
The table above, is intended to give a very rough number, so you can take a graph of global temperature anomalies, which is baselined to something other than pre-industrial (as per Paris Agreement I’m using 1850-1900 to be “Pre-Industrial”), and lookup the adjustment needed. E.g. if the graph you are looking at is using the 1951-1980 baseline, then add “0.3°C” to the Y-axis numbers to get the pre-industrial equivalent.
Baseline Conversions – Specific to a given dataset
The table above, is a slightly more detailed table, compared to the “Quick and Dirty Adjustment Table”.
This table:
- Uses 2 decimal places (More accurate)
- Also takes into account the dataset which the table is using.
E.g. if the baseline is 1981-2010, and the dataset used is “Copernicus ERA5” (See GMST Data Sets), then add 0.88°C to the Y-Axis numbers to get the anomalies relative to Pre-Industrial.
E.g. if the baseline is 1981-2010, and the dataset used is “HadCRUT5” (See GMST Data Sets), then add 0.71°C to the Y-Axis numbers to get the anomalies relative to Pre-Industrial.
Convert Copernicus 1991-2020 baseline to Copernicus 1850-1900
The table below is specific to Copernicus ERA-5 Data, who ofter prefer the 1991-2020 baseline for their graphics. The previous adjustment tables (sections above), are useful when comparing complete years. With ERA-5 Data, you need to watch out for plots which are for individual months. Look at Examples for Baseline Adjustment (search for “Ref-Cop-1991-2020-Jan”), and you will see the “year to date” graph has a slight difference from the “Monthly Anomalies” graph. Notice the difference in how low the curve goes in June/July. See also Copernicus 1850-1900 Baseline – Daily GMST Anomaly for why things are different if you compare whole years, vs individual months.
Convert Copernicus 1981-2010 baseline to Copernicus 1850-1900
This is the same as the previous graph, and is specific to Copernicus ERA-5 data, but uses the 1981-2010 baseline
Evidence:
See Baseline Adjustment Evidence (and search for the “Evidence Reference” E.g. “Ref-Cop-1991-2020-Sep”), to for links to published articles, which confirm that the Baseline adjustment values in the table above are correct. Let me know if you dispute any of the values, by posting a comment in the one of the blog posts, or by posting on BlueSky (See About page)
Examples
See Baseline Adjustment Examples (and search for the “Evidence Reference” E.g. “Ref-Cop-1991-2020-Sep”). I don’t have examples for every variant, but enough to get the idea.
The examples below show how to get “Paris Agreement” global warming values.
For example, take a graph which has a baseline (such as 1991-2020), and adding a value to get “Paris Agreement” global warming anomalies. E.g. adjustments, to give you the values for a “Pre-Industrial” baseline. (E.g. 1850-1900).