The UNs IPCC starts with the unproven assumption that CO2 in the atmosphere controls the climate, with no evidence that has ever been true in the past 4.5 billion years.
But water vapor is 95% of total greenhouse gases -- and much more important than carbon dioxide, which is under 4%.
In 1980 very rough measurements showed a slight 100-year warming trend of the average temperature.
Some scientists insisted that 100-year trend had to be caused by a greenhouse effect from CO2 -- and, believe it or not, the global warming itself was said to be proof of the greenhouse effect.
That was not science -- it was pure speculation.
A thirty-year period of warming from 1910 to 1940 can't be blamed on CO2, because almost no CO2 was added to the atmosphere during the period, as required to create greenhouse warming.
The large increase of CO2 from 1940 to 1975 did not cause any warming at all.
1900 to 2015 consisted of these trends:
(1) A flat average temperature trend to 1910,
(2) Rising trend from 1910 to 1940,
(3) Declining from 1940 to 1975,
(4) Rising from 1975 to 2003 (mainly rising from 1993 to 2003), and
(5) Flat from 2003 to 2015
Within these trends are periodic El Nino peaks and La Nina troughs that affect the Pacific Ocean.
El Niño Southern Oscillation = irregular wind and sea surface temperature variation over the tropical eastern Pacific Ocean.
An El Nino brings high temperatures and drought to eastern Australia and Indonesia -- the opposite effect, La Niña, brings heavy rainfall and storms.
No one claims local El Ninos have anything to do with the greenhouse effect.
The spacing between El Nino peaks is about five years.
El Nino peaks, separated by La Nina valleys, are usually considered to be statistical noise, and are often smoothed on a chart by a running mean.
No one thinks about them if they are smoothed by a moving average ... but they are local weather cycles large enough to affect the global average temperature, at least temporarily.
A common assumption is that El Nino and La Nina are a mirror-image cycle -- their effects on the average temperature cancel each other over a full five year cycle.
But ... the global warming effect of several El Ninos in the 1990s was not completely reversed by the La Ninas that followed them.
Perhaps that fact explains the warming in the 1990s better than carbon dioxide greenhouse warming?