Observational uncertainty, errors, biases, and estimation discrepancies in longwave radiation may be 100 times larger than the entire accumulated influence of CO2 increases over 10 years. This effectively rules out clear detection of a potential human influence on climate.
The anthropogenic global warming (AGW) hypothesis rides on the fundamental assumption that perturbations in the Earth’s energy budget – driven by changes in downward longwave radiation from CO2 — are what cause climate change.
According to one of the most frequently referenced papers advancing the position that CO2 concentration changes (and downward longwave radiation perturbations) drive surface temperature changes, Feldman et al. (2015) concluded there was a modest 0.2 W/m² forcing associated with CO2 rising by 22 ppm per decade.
Again, that’s a total CO2 influence of 0.2 W/m² over ten years.
In contrast, analyses from several new papers indicate the uncertainty and error values in downwelling (and outgoing) longwave radiation in cloudless environments are more than 100 times larger than 0.2 W/m².
In other words, it is effectively impossible to clearly discern a human influence on climate.
1. Kim and Lee, 2019 Measurement errors of outgoing longwave radiation (OLR) reach 11 W/m², more than 50 times larger than total CO2 forcing over 10 years. Cloud optical thickness (COT) and water vapor have “the greatest effect” on OLR – an influence of 2.7 W/m². CO2 must rise to 800 ppm to impute an influence of 1 W/m².
Image Source: Kim and Lee, 2019
2. Kato et al., 2018 Downward longwave radiation (DLR) responds to variability in water vapor and cloud. (CO2 isn’t mentioned in the paper as a factor influencing DLR.) CO2 rose by 20 ppm during 2005-2014, but total DLR was negative (-0.2 W/m²) during this decade, insinuating rising CO2 had no net warming climate impact. Uncertainty in DLR is 6 W/m² per year, whereas CO2 forcing is just 0.02 W/m² per year – 300 times smaller.
Image Source: Kato et al., 2018
3. Wild et al., 2019 Observations vs. model bias/discrepancy ranges in downward longwave radiation span between 22 W/m² to 26 W/m², which is 120 times larger than CO2’s total influence over 10 years.