State of the Climate in 2019: Global cloud trends

September 8, 2020 | Leanne Avila

Research on clouds is vital to our understanding of the hydrological cycle–for predicting and monitoring droughts and flooding–and the global energy budget and the effect of clouds on Earth’s climate.

Scientists from the Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin–Madison and National Oceanic and Atmospheric Administration (NOAA) Advanced Satellite Products Branch (ASPB) stationed at CIMSS recently contributed an update on global cloudiness trends to the State of the Climate in 2019 report published by the American Meteorological Society (AMS).

“The average global cloudiness doesn’t tend to change too much year-to-year, but the global distribution of cloudiness can vary quite a bit,” noted Mike Foster, CIMSS researcher and the lead author on the global cloudiness section of the report.

That distribution can lead to unique and severe impacts across the globe, as it did in Australia in 2019.

In general, the distribution of clouds across the globe are often impacted by changes in circulation patterns such as the El Niño–Southern Oscillation (ENSO), which affects winds and sea surface temperatures in and near the tropics through El Niño and La Niña. Foster explained that in 2019 ENSO was less of a factor than another similar pattern known as the Indian Ocean Dipole (IOD), which alters sea surface temperatures in the Indian Ocean.

“When the IOD is in a positive phase, eastern Africa tends to be more cloudy and Australia is less cloudy, compared to average. The positive IOD in 2019 was one of the strongest events seen in decades, and it led to some very dry conditions in Australia that contributed to the massively destructive wildfires,” stated Foster.

Annual global cloudiness anomalies for 1981-2019. The anomaly is defined as the annual value minus the mean, derived for a period common to the satellite records. Credit: Mike Foster, CIMSS

Long-term studies of clouds with highly accurate measurements are critical to monitoring their trends and impacts on the climate. Foster mentioned how small changes in any number of cloud parameters–coverage, thickness, cloud height–can have a dramatic effect. Understanding these impacts remains key in their research.

“In fact, the treatment of clouds, and specifically cloud feedbacks, is the largest source of deviation among climate models for future climate scenarios,” stated Foster.

State of the Climate is published by the AMS as a special supplement to the Bulletin of the American Meteorological Society (BAMS). This year marks the 30th such report. Assisted by CIMSS, ASPB, and other colleagues, Foster has been contributing updates on global cloudiness to the report since 2008.

Find the State of the Climate in 2019, as well as past years’ reports online at: