2021 Global Mean Surface Temperatures

I keep a spreadsheet of the major Global Mean Surface Temperature (GMST) datasets. The numbers for December 2021 and the year of 2021. So I plotted the data from NASA, NOAA, JMA, Berkeley Earth (BEST), and HadCRUT5. The year ended up basically in a statistical tie with 2018 as the 6th warmest year on record and both 2018 and 2021 are the warmest La Nina years on record. It's amazing to me how much agreement there is between these datasets. To illustrate, I calculated the average of all of the above and plotted the average with the 95% confidence intervals from the HadCRUT5 dataset. The average seems to consistently fall within the 95% confidence interval for HadCRUT5.

I also decided to do a little calculation to update the when we can expect to hit 1.5 C if we continue at the same pace. To estimate this I used basically the same method used in the IPCC 1.5 C report. I took the HadCRUT5 dataset and calculated 30 year trends (centered) through 2005. Then I took the 30 year trend (0.225 C/decade) and projected that through the end of 2021. This puts Dec. 2021 at 1.25 C warmer than the 1850-1900 mean. If we project from that date forward at 0.225 C/decade, warm up to 1.5 C in 0.25/0.225 = 1.1 decades or 11 years, so 2032. If we continue warming at this rate, then we would hit 2 C warming in another 0.5/0.225 = 2.2 decades - 2032 + 22 = 2054.

I also decided to plot 30 year trends for each of these datasets, so you can track how they are changing. There has been a clear acceleration of warming in recent decades, and all datasets show the most recent 30-year trend to be above 0.2 C/decade. This seems like a pretty remarkable agreement.

All of these graphs were generated with a simple spreadsheet using data found freely online. The data is all available as either txt, csv or Excel files, but I actually just use Google Sheets because it's extremely easy to open up the data and have it show properly as a table. The calculations above are easy to do. The point is here that these organizations are making their data readily available, and you can also check up on everything I do and all the graphs I share. It turns out that the 8 warmest years on record all occurred in the last 8 years. At 0.2 C/decade, warming rates are not fast enough to exceed natural variability from ENSO - La Niña years are still likely to be less warm than the El Niño year that immediately preceded it, but the planet is still warming nonetheless. In fact, El Niño years and La Niña years are warming at about the same rates. One of these days, I'm going to have to tag these years by their ENSO classification to generate this graph on my own.





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