More observational evidence emerges showing CO2’s effects are too small to drive climate.
The oft-cited Feldman et al. (2015) paper proposes to isolate the CO2 impact by only considering a “clear-sky” atmosphere at two sites: the North Slope of Alaska and the Southern Great Plains (USA). In other words, that study can only claim to assess what occurs in an imaginary atmosphere where clouds do not exist – even though clouds are present about 60-70% of the time in the real-world atmosphere.
Results indicated that CO2 enhances the downwelling longwave radiative forcing (DLRF) trend, the greenhouse effect, by just 0.2 W/m² per decade (accompanying a 22 ppm CO2 increase from 2000 to 2010).
Image Source: Feldman et al., 2015
But a 2025 paper quietly published in Nature also assessed the contributors to the DLRF trend from 1996-2018 at the Southern Great Plains, even extending their measurements to all land surfaces across the globe from 60°S to 60°N.
But instead of employing only a simulated atmosphere where clouds do not exist, Liu and colleagues provided the all-sky values. So, unlike the Feldman paper, they employed the real-world atmosphere which have clouds contributing to (and dominating) the DLRF trend.
They found observed trends in downwelling longwave show the cloud DLRF contribution actually serves to reduce the greenhouse effect impact by -0.77 to -1.77 W/m² per decade.
Since the CO2 contribution enhances the trend by only 0.2 W/m² per decade, clouds therefore have been observed to easily outclass and even nullify (net) the effect of CO2 increases.
The tiny “finger printed” (FP) decadal effect of CO2 in a real-world, all-sky atmosphere is illustrated (red bar) in the DLRF trend (W/m² per decade) graph. Notice how insignificant the CO2 contribution is compared to the effect of clouds (gray bar).
Perhaps this is why Feldman and colleagues chose to use an imaginary-world, clear-sky-only atmosphere instead of a real-world, all-sky atmosphere.
[…] Related: 2025 Study: Cloud Effects Reduce Downwelling Longwave Radiation, Overriding The CO2 Impact […]
It’s important to deconstruct Feldman et al. 2015 because it was touted in the press as silencing “Climate Deniers” and as giving scientific proof of the greenhouse gas effect, once and for all.
This paper claims to prove rising CO2 in the atmosphere increases down-welling infra-red radiation (DWIR), thereby warming the earth’s surface. The claim is based on observations from 2 sites, in Alaska and Oklahoma. Let’s examine the case made.
Observation: In Alaska and Oklahoma CO2 and DWIR are both increasing.
Claim: Additional CO2 is due to fossil fuel emissions.
Claim: Higher DWIR is due to higher CO2 levels.
Claim: Global DWIR is rising.
Claim: Global surface temperatures are rising.
LL Conclusion: Fossil fuel emissions are causing Global surface temperatures to rise
There are several issues that undermine the report’s conclusion.
Issue: What is the source of rising CO2?
Response: Natural sources of CO2 overwhelm human sources.
The sawtooth pattern of seasonal CO2 concentrations is consistent with release of CO2 from the oceans. Peaks are in March when SH oceans are warmest (60% of world oceans), and valleys are in September when NH oceans are warmest. In contrast biosphere activities peak in January in SH and July in NH.
CO2 content of the oceans is 50 times that of the atmosphere, resulting in the sawtooth extremes. Human emissions are ~5 to 7 Gigatons compared to ~150 Gigatons from natural sources.
Issue: What is the effect of H2O and CO2 on DWIR?
Response: H2O provides 90% of IR activity in the atmosphere.
The long term increase in DWIR can be explained by increasing cloudiness, deriving from evaporation when the sunlight heats the oceans. A slight change in H2O vapor overwhelms the effect of CO2 activity, and H2O varies greatly from place to place, while the global average is fairly constant.
Issue: What is the global trend of DWIR?
Response: According CERES satellites, DWIR has decreased globally since 2000, resulting in an increasing net IR loss upward from the surface.
Globally, Earth’s surface has strongly strengthened its ability to cool radiatively from 2000 to 2014 (by about 1.5 W/m2 or ~1 W/m2 per decade) according to CERES. The increased upward heat loss from the surface is matched by decreasing trend of DWIR globally. And this is in spite of significantly increasing atmospheric content of both CO2 and H2O (WV & clouds) + allegedly rising temps since 2000.
Conclusion:
The rise in CO2 is almost all from natural sources, not fossil fuel emissions.
IR activity is almost all from H2O, not from CO2.
Global DWIR is lower this century, and the surface heat loss is less impeded than before.
Global surface temperatures are not rising with rising fossil fuel emissions.
In fact, you need only apply a little critical intelligence to this paper, and it falls like a house of cards.
Amazing post! I am essentially satisfied with your great work. You put truly supportive data.
[…] From NoTrickTonet […]