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A surprise in the data

A recent edition of The Economist featured an article on the current (albeit coming to an end) strong El Nino in the Pacific and the impact or otherwise that a warming climate system might be having on it. The article asks many questions and even delves into the recent controversy about the so-called pause in global warming. The author notes;

The sweltering temperatures in recent months may help settle debates over a supposed “pause” in global warming that occurred between 1998 and 2013. During that period the Earth’s surface temperature rose at a rate of 0.04°C a decade, rather than the 0.18°C increase of the 1990s.

Global temperature data can be challenging to analyse, but one very simple analysis I put together showed quite a surprising result. El Nino events can be categorised, with the events of 1997-98 and 2015-16 both listed as Very Strong. 1972-73 and 1982-83 were also Very Strong events, giving a total of four such events over the last 40 years. Each of these events led to a temperature spike in the global record as reported by the US National Oceanic and Atmospheric Administration (NOAA). The data is as follows;

A quick plot of this data shows an almost perfect linear trend over recent decades, with the Very Strong El Nino same year global temperature anomaly rising monotonically at 0.18°C per decade. There is no sign of a pause in warming or acceleration, at least over the last 40+ years. Extending the trend into the 2030s indicates that a future Very Strong El Nino event in that period would result in a 1.3°C temperature rise, which is about the equivalent to 1.5°C above pre-industrial levels in the NOAA time series (using late 19th century as a proxy for pre-industrial).

Casting back a bit further to a much earlier Very Strong El Nino, brings us to 1926. This was reportedly an extreme event for the period and corresponded with the most severe drought in tropical South America during the 20th century. Including it in the chart above as well as a further point in 1963, shows the current linear trend still holding back to 1960, but not into the 1920s. At this time atmospheric carbon dioxide was only just beginning to rise. But the fact that the 1920s El Nino is matched by a presumably elevated 1960s El Nino perhaps points to just how severe that event must have been.

The data for the last half century for comparable El Nino event years and coinciding with a rise in atmospheric carbon dioxide from 315 ppm to 400 ppm (vs. 275 ppm to 315 ppm over the century before that) indicates that the underlying surface temperature trend is rising consistently, despite the noise associated with year on year fluctuations of the Southern Oscillation (El Nino and La Nina) and other phenomena. This data noise has given rise to claims of both no global warming and accelerating global warming. The reality is sobering enough, even without the histrionics from some observers.

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