The last 40 years of global temperature changes can be radiatively explained by a natural reduction in cloud cover.
From 1979 to 2011, satellite data provide documentation of a reduction in cloud cover and aerosol depth that allowed an additional 2.3 W/m² of positive shortwave energy to be absorbed by the Earth’s surface rather than reflected to space.
This change in absorbed solar radiation can account for the energy imbalance and warming during this period far better than the much smaller 0.2 W/m² forcing associated with a +22 ppm CO2 change over 10 years (representing just 10% of the overall trend in downwelling longwave).
Image Source: Herman et al., 2013
Other satellite observations reveal a pronounced 6.8 W/m² positive solar forcing particularly concentrated during the 1984-2000 period due to a decrease in reflected shortwave energy (via clouds).
Image Source: Goode and Palle, 2007
From 2014 to 2017, the reduction in cloud cover resulted in an additional 0.83 W/m² shortwave forcing, which explains the imbalance and the stark warming during this post-“pause” period.
Image Source: Loeb et al., 2018
The reduction in cloud cover and positive shortwave forcing trend can also explain the post-1995 ice melt pattern for the Greenland ice sheet.
Image Source: Hofer et al., 2017
Image Source: Simpkins, 2017
A new paper underscores the salience of cloud cover reduction in explaining not only the modern warming but the temperature variation that occurred in recent decades.