A new study indicates nearly all the Northern Hemisphere and Tropical warming in the last 40 years occurred by the late 1990s.
CO2 has risen by about 50 ppm since 1998 (367 to 418 ppm).
Interestingly, upper-air measurements of temperature from balloon-borne sensor radiosonde data, shown below in the image from a new study (Madonna et al., 2022), suggest there was more warming from the early 1980s to late 1990s – when CO2 only rose about 25 ppm (341 to 367 ppm) – than there has been this century.
Radiosonde measurements appear to depict mostly flat temperature trends since 1998 in both the Northern Hemisphere (25°N to 70°N) and tropics (25°S to 25°N).
Image Source: Madonna et al., 2022
About those CO2-Temperature mismatches…
From 1905-1945 annual human CO2 emissions hovered around one gigaton of carbon, or 1 GtC/yr.
But according to the graphical depiction of global sea surface temperatures (SSTs) shown in Kennedy et al., 2019, SSTs rose about 0.6°C to 0.7°C during these 40 years.
Emissions grew from 1 to 5 GtC/yr from 1945 to 1975 and then from 5 to 9 GtC/yr from 1975 to 2012. But during these 30- and 37-year periods SSTs cooled -0.1°C and warmed 0.3°C, respectively.
So in the 67 years from 1945 to 2012, net global SST warming was only about 0.2°C (0.03°C per decade) even though human CO2 emissions exploded from 1 to 9 GtC/yr during these decades, whereas the global SST warming was about ~0.65°C (0.16°C per decade) in the 40 years from 1905 to 1945 when CO2 emissions were a relatively flat 1 GtC/yr.
If human CO2 emissions were driving Earth’s surface temperature trends, why is there such a mismatch between the trajectory of the emissions versus the surface temperatures?