Let's walk through the steps once more. The combination image below shows that the February 2019 temperature was 0.93°C above a 1951-1980 baseline (left) and 1.21°C above a 1885-1915 baseline (right), a difference of 0.28°C.
In other words, when using a baseline that is centered around 1900, the data should be adjusted by 0.28°C. In the image below, the gold graph uses 1951-1980 as baseline and two linear trend are added, one using data starting in 1880 (gold) and one using data starting in 1900 (blue).
Both linear trends are out of line with the recent temperature rise, the gold trend even more so than the blue trend, illustrating that starting a linear trend from an earlier year can make an analysis worse.
As said, if we want to use a baseline that is centered around 1900, the data should be adjusted by 0.28°C, and this is what the green graph does. A 4th-order polynomial trend is added that lines up perfectly with zero at the year 1900.
Further adjustment is needed for a 1750 baseline, which better reflects preindustrial as in the Paris Agreement. As discussed in an earlier post, this could result in an additional adjustment of 0.3°C.
Furthermore, have another look at above maps. Much of the extreme anomalies are in line with changes to the Jet Stream, as also illustrated by the insert. More cold air escaping the Arctic and more warm air entering the Arctic are both speeding up Arctic warming. In the map on the right, much of the Arctic is left grey, since no data are available for the Arctic around 1900, but the Arctic should not be left out of the picture and adding a further 0.1°C adjustment seems appropriate to better include the Arctic.
Finally, the NASA temperatures for oceans are the surface temperatures of the water, but it makes more sense to use air temperatures close to the water, which likely adds a further 0.1°C. This adds up a total adjustment of 0.78°C as applied in the red graph, which also has an 8th-order polynomial trend added.
Trend analysis that uses data going back many years can only be part of the picture; it's also important to anticipate changes that could occur in the near future. When taking the many feedbacks, tipping points and further warming elements more fully into account, the temperature could rise even more strongly than is pictured in the red trend in the image at the top and there could be an 18°C rise by the year 2026. In the graph at the top, the vertical axis is cut off at 5°C, since life on Earth will already have disappeared by then (see box on the right).
|[ from an earlier post ]|
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• Climate Plan