In 2020, fuel regulations abruptly reduced the emission of sulfur dioxide from international shipping by about 80% and created an inadvertent geoengineering termination shock with global impact. On January 1, 2020, new international regulations on the sulfur content of shipping fuel reduced the maximum sulfur content from 3.5% to 0.5%. Ship-emitted aerosols and sulfur dioxide, which creates atmospheric aerosols, caused linear trails of brighter oceanic clouds. The reduction of marine aerosols reduces the cloud cover, allowing more sunlight in to warm the ocean surface.This paper estimates the regulation leads to a radiative forcing of 0.2 Wm−2 averaged over the global ocean. The amount of radiative forcing could lead to a doubling (or more) of the warming rate in the 2020 s compared with the rate since 1980. The regulation change will make the 2020 s anomalously warm.

This paper that shows the patterns of clouds and temperature indicate that the cloud cover decrease since 1987 could not have been caused by the increased surface temperature. The latest versions of most climate models show increased climate sensitivity to CO2 by assuming that the recent decrease of cloud cover was due to increasing temperatures which amplifies the direct CO2 warming effect. Cloud and temperature patterns over short time scales (a few months) indicate that warmer temperatures cause more cloud, not less. The climate models, which have zero or negative cloud impact independently from CO2, need to take this into account in order to avoid over-estimating the influence of CO2.

Two new experiments at CERN using the CLOUD chamber (Cosmics Leaving OUtdoor Droplets) near Geneva, Switzerland show that the pre-industrial earth was cloudier than previously assumed. Most climate scientists assumed the skies were sunnier before the use of coal and other fossil fuels because sulfur dioxide released by burning the fuels oxidizes to sulfuric acid which creates aerosol particles that seed cloud formation. One experiment shows that organic vapours emitted by trees produce abundant aerosol particle in the atmosphere in the absence of sulfuric acid.It was previously thought that sulfuric acid is the key player in cloud formation. Since clouds reflect sunlight back into space, any extra clouds could have offset a portion of greenhouse gas warming. A second CLOUD experiment showed that the small aerosol particle could rapidly grow to sizes big enough to seed cloud droplets. Another group of researcher measured the concentrations of sulfuric acid and organic molecules in the Swiss Alps. They observed that aerosols formed from organic molecules without sulfuric acid. The new results show that modelers can 't offset as much CO2 forcing with aerosol cooling so climate sensitivity to CO2 emissions is lower than modelers assumed and future temperature increase will be much less than currently projected by climate models.

Global average ocean temperature variations to 2,000 m depth during 1955 - 2011 are simulated with a 40 layer 1D forcing-feedback-mixing model. The model included ENSO-related changes in cloud cover preceding the temperature change. The time lag and amount of cloud changes were adjusted to make the best match to the ocean temperature and the CERES satellite observations. When the cloud effects of ENSO are included, the equilibrium climate sensitivity falls from 2.2 to 1.3 Celsius for double CO2, or a 41% reduction. The ENSO process causes clouds to change, causing a temperature change. Part of the 20th century warming was caused by ENSO activity. ENSO is the El Niño-Southern Oscillation, a recurring climate pattern involving changes in the temperature of waters in the tropical Pacific Ocean, or El Niño (warming) and La Niña (cooling).

Stereo measurements from a NASA satellite show the global cloud height has dropped about 1% from 2000 to 2010, allowing them to radiate more heat to space which cools the planet. The drop in average cloud height is largely due to fewer high clouds. Low clouds radiate more energy to space than high clouds.

This paper by Dr. Roy Spencer examines radiative feedbacks and presents a way to separate the feedback signals from radiative forcing signals in satellite data. It shows that the radiative forcings from cloud changes give the illusion of a positive cloud feedback. The true feedback signal found in the satellite data shows a strong negative cloud feedback to temperature changes of 6 W/m2, equating to a climate sensitivity of 0.6 Celsius. This makes CO2 emissions a non-issue.