A very quick overview of the global temperature evolution.
According to climate science researchers, there have been several surges in global temperatures to higher levels since 1850.
By plotting the 1850 to July 2023 monthly NOAA global anomalies, visually it becomes clear when the temperature surges upward took place.
There do exist different numeric and statistical manners in which to identify temperature shifts, but the temperature level shifts on this chart were identified simply by the self-evident grouping of the majority of anomalies for a given time period. (See anomalies grouped within black dashed lines.)
A summary of the five temperature periods from the chart:
Period1: From January 1850 through April 1937, this was an extended time span for both cooling and warming bursts but overall this 87+ year period experienced a small cooling trend of -0.01°C/decade. Notice that over the period’s last 20 years, the global anomalies were rising.
Period2: Global temperatures were shifted up to a new base level from May 1937 through October 1976 (39.5 years). Despite the prominent shift up at the beginning of the period, there was a small cooling trend of -0.02°C/decade for the entire period.
Period3: From November 1976 through December 1996 (20.2 years), the first extended modern warming trend was established. There were two brief cooling spans during this period but overall the warming trend was +0.10°C/decade.
Period4: From January 1997 through August 2014 (17.7 years), the warming trend increased to +0.17°C/decade level, again with two cooling spans intermixed during the 17+ years.
Period5: From September 2014 through the end of July 2023 (8.9 years), the warming trend has been significantly reduced – almost being flat – when compared to the two prior warming periods.
While there are those who suggest that CO2 emissions from fossil fuel combustion are to blame for the significant shifts in global temperatures over the five different periods, the empirical science does not support the hypothesis that a trace atmospheric gas can cause abrupt changes.
A more likely explanation for the shifts is the natural oscillations and weather variations that are part and parcel of the world’s climate.
For example, the well-known climate warming oscillation called ‘El Niño‘ has taken place during all the periods at an average frequency of every five years. Climate researchers have noticed that climate temperature step-upward shifts seem to follow significant El Niño episodes.
Finally, it is possible to reduce the five periods to two very long-term periods: one cooling/flat and one warming. This can be accomplished if one strictly uses the change of the slope of the linear trend from negative to positive at a specific point over the entire length of time since 1850.
For the first long-term period – from1850 to December 1940 – there was a very slight negative slope (i.e., cooling). That amounts to 90.9 years with a trend that was practically flat, thus indicating that there had not been any significant warming over the 90+ years since the Little Ice Age (LIA), which is thought to have ended around 1850.
Using NOAA data, the very long-term positive warming trend starts in January 1941 and continues for 82.5 years, until the end of July 2023.
And if NOAA records are accepted as a trustworthy history of world temperatures, it would then be logical to conclude that a robust, significant temperature recovery from the extended LIA cold really did not begin until the early 1940s.
Notes: Excel used for all calculations and plotting. Source of NOAA monthly global temperature anomalies.