This month’s open thread. Try to stick to climate topics.
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298 Responses to "Unforced variations: July 2025"
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And when truth is that rare, even a feather can feel like thunder.
Interesting analysis (courtesy of Media Matters) of coverage surrounding the horrific death and destruction a week past from a sudden catastrophic flood in Texas and implications involving climate change and preparedness:
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“National TV news covered the catastrophic Central Texas floods with depth and urgency, but connections to climate, preparedness, and policy were uneven”
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https://www.mediamatters.org/broadcast-networks/national-tv-news-covered-catastrophic-central-texas-floods-depth-and-urgency
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Idealized model experiment using Amazon deforestation as a proxy for biogeophysical destruction (preprint):
https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3221/
Arim Yoon, Cathy Hohenegger, Jiawei Bao, and Lukas Brunner
Max Planck Institute for Meteorology
This experiment contrasts “Control” (intact biosystem) and “Destroyed” (desertified) cases to examine how biogeophysical changes affect regional climate.
Control vs Destroyed cases
Energy budget and Temperature:
– Reduced evapotranspiration results in more surface energy being redistributed as sensible heat flux
– Surface SW down increases 30.93 W/m2 (less cloud), Surface SW up increases 16.48 W/m2 (greater surface albedo)
– Surface LW radiative cooling increases 32.59 W/m2 (hotter temps, longer duration of clear sky).
– Surface net radiation decreases 18.14 W/m2 (sensible heat + 38.21 W/m2, latent heat flux – 59.37 W/m2)
On average, the near-surface temperature rises significantly by about 3.84C, and the daily minimum temperature after destruction becomes similar to the daily maximum temperature before biogeophysical annihilation.
And so we see again the critical role of energy budget partitioning (not just net radiation) on temperature – radiation budget down 18 W/m2, Temperature up 4 degrees C.
Precipitation & Dynamics: Control vs Destroyed Cases & Hypotheses
Hourly precipitation becomes more extreme in the destroyed case than in control, with an increased occurrence of both no rain and intense rainfall. These changes are driven by enhanced moisture convergence that strengthens vertical velocity.
No rain almost triples, and violent rain increases by a factor of 1.5.
The changes in the tails of the precipitation distribution can be attributed to the fact that it is more difficult to trigger convection in the destroyed case, leading to more violent outbursts when convection does happen.
The increase in violent rain is primarily driven by stronger updrafts and not by enhanced total column water vapor.
Convective available potential energy (CAPE) vs Moisture Convergence
CAPE ranges from 1500 to 3000 J kg-1 in Control
Mean CAPE values around 1000 J kg-1 in destroyed mode
The increase in drier near-surface conditions is a direct consequence of the decrease in evapotranspiration following deforestation, whereas the reduction in CAPE follows from the raised lifting condensation level and level of free convection.
Alongside the decrease in CAPE, Convective Inhibition (CIN) increases, with the mean value rising from 27 J kg−1 to 111 J kg−1. The environment is more inhibited for convection, and this explains why more no-rain events appear. After all, the environment, in general, becomes less favorable to convect thermodynamically, requiring a stronger dynamical driver to precipitate.
Updraft strength is attributed to the convergence that forces ascent (mechanical updraft). The tails of the convergence distribution are heavier after biogeophysical carnage, aligning with the simulated increase in violent precipitation. In other words, there are more extreme dynamic gradients building in atmosphere.
This reflects a shift from thermodynamic to dynamic triggers of convection: a more inhibited, unstable environment punctuated by violent outbreaks.
It all seems pretty common sense really – as land parcels are made more un-like ocean, thermal and moisture contrasts increase, perhaps influencing all the way to the scale of planetary waves and global circulation. This is opposite to the standard approach of large scale determinism, and the artificially narrow focus on radiative forcing and feedback to explain changing climates.
It is oft discussed in these RC comment threads that the CERES data shows an increase in the Earth’s Energy Imbalance (EEI) through the recorded period 2000-on. The data shows this reaching a value of EEI=+1.34m^-2 from a start value of EEI=+0.31Wm^-2 (these de-wobbled using 3-year averages of de-seasonalised data: NOTE this data shows a pretty good linear trend of ΔEEI=+0.44Wm^-2/decade+/-0.10[2sd], a linearity which is more evident with the monthly de-seasonalised CERES data than the more commonly used 12-month rolling averages). Thus the CERES record shows a +1.02Wm^02 EEI increase thro’ the period 2001-24, an increase which can be attributed to +0.14Wm^-2 solar flux, +1.87Wm^-2 decreased albedo (which includes a small surface component of perhaps +0.12Wm^-2 – this value scaled from Goessling et al (2024) FigS3 with their attenuation factor of 3) and -0.99Wm^-2 negative feedback from ΔT.
There has been some rather cursory** attributions for the increasing albedo component of the EEI with aerosol reductions featuring large. Perhaps a more nuanced view (that is Hansen’s “must be provided by some combination of the two” ) is that the albedo component includes both the aerosol effect and global warming feedback (cloud and ice) but, as both aerosol & feedbacks would point to a larger ECS, the proportion of each within the albedo decline is somewhat immaterial.
(** The 2023 “bananas” has seemingly prompted more detailed attribution work but this focusing on the latter period of the CERES record rather than the full period since 2000.)
I see no work trying very hard to disentangle the CERES numbers into the aerosol contribution and the albedo feedbacks contribution.
One approach to this disentanglement is to consider that the two hemispheres are reasonably separate from each other climatically. And with the NH & SH being very different in land mass, population, rate of ΔT under AGW, etc, their various aerosol loadings will be radically different and importantly for the disentanglement, the change in aerosol emissions through recent decades is also radically different (see world map of ΔAOD 2005-2021HERE). Yet despite the NH & SH differences, it has been noted that they have had very similar levels of albedo and additionally the NH & SH albedo decrease since 2000 is also very similar (see graphic showing NH & SH reflected sunlight HERE – Posted 13th July 2025) suggesting there is little of the change in albedo that can be attributed to changes in aerosol emissions through this period.
However, there are some increasing differences, certainly in the last few years and that does deserve some numbers.
The 5-year-averaged numbers for reflected sunlight in the CERES data 2000-25 decreases by 1.58Wm^-2(global), comprising NH 0.98Wm^-2(g) and SH 0.60Wm^-2(g), thus the NH value just 0.38Wm^-2(g) greater. And just 0.27Wm^-2(g) has appeared since the start of 2020.
The CERES data does allow for similar analysis for different zones/sectors and such analysis may yield a value attributable to those 2020 Shipping Regs. Up-thread, an earlier assessment of the reflected sunlight (OSR) CERES data attributed ΔF[global] +0.17Wm^-2 to the zones/sectors applicable to the Shipping Emissions Regs. An analysis of the comparisons as per this NH:SH comparison provides a further step towards identifying the true Shipping Regs forcing.
So how bigly/littlerer will it prove to be?