James Hansen and Pushker Kharecha - Large Cloud Feedback Confirms High Climate Sensitivity

[OKIsItJustMe]

https://www.columbia.edu/~jeh1/mailings/2025/CloudFeedback.13May2025.pdf

Fig. 1. Earth’s albedo (reflectivity, in percent), seasonality removed¹ ² ³ ⁴

Large Cloud Feedback Confirms High Climate Sensitivity

James Hansen and Pushker Kharecha 13 May 2025

Abstract. Earth’s albedo (reflectivity) declined over the 25 years of precise satellite data, with the decline so large that this change must be mainly reduced reflection of sunlight by clouds. Part of the cloud change is caused by reduction of human-made atmospheric aerosols, which act as condensation nuclei for cloud formation, but most of the cloud change is cloud feedback that occurs with global warming. The observed albedo change proves that clouds provide a large, amplifying, climate feedback. This large cloud feedback confirms high climate sensitivity, consistent with paleoclimate data and with the rate of global warming in the past century.

A strange phenomenon occurred in response to our recent paper, “Global warming has accelerated: are the public and the United Nations well informed?” ⁵ A few reports appeared in the media the next day, but, almost uniformly, these reports dismissed our conclusions as a fringe opinion, out of step with the larger scientific community, and thus there was no continuing discussion of the issues raised in our paper. How did the media arrive at that conclusion, and is that conclusion truly representative of the wider scientific community? Are there important repercussions for the public of the media’s approach for assessing a climate research paper, especially for today’s young people, indeed, for the future of all people? The answer to the latter question, we conclude, is “yes.”

Given this last conclusion, we must make special effort to clarify the situation. Perhaps the best way is to summarize our analysis, aiming for a wider community, beyond the handful of climate scientists that the media have come to rely on. Our analysis puts equal emphasis on information on climate change extracted from (1) observations of ongoing climate change, (2) global climate models (GCMs), and (3) Earth’s long-term climate history (paleoclimate data). We used all three of these methods in our paper to arrive at three independent analyses of climate sensitivity, with each method concluding that climate sensitivity is high, much higher than the best estimate (3°C for doubled atmospheric CO₂ ) of IPCC (Intergovernmental Panel on Climate Change).

This communication concerns one of the ongoing climate observations: Earth’s darkening (declining reflectivity) as seen from space. We then discuss the difficulty of communicating with the public.



Earth’s albedo (or reflectivity) is the portion (percent) of incoming solar radiation that is reflected back to space. As shown in Fig. 1, in the period of precise satellite data (since early 2000), Earth’s albedo has decreased about 0.5%. We described this change as a BFD ⁶ ⁷ because it has staggering implications. Solar radiation reaching Earth is about 340 W/m² , averaged over Earth’s surface, so the 0.5% albedo decrease is a 1.7 W/m increase of absorbed solar energy, much larger than the estimated potential drift² …

[WestMichRad]

1. K&R

Disheartening but not surprising.

Is this an actual quote from the article? “We described this change as a B F D because it has staggering implications.”

[OKIsItJustMe]

2. The entire post is straight from the article.

The BFD comment comes from this video (at about the 12 minute mark):