Low-Altitude Cloud Cover Decline Linked to Rise in Temperature

A recent study has highlighted that declining low-altitude cloud cover has contributed about 0.2°C of the nearly 1.5 degrees Celsius rise seen in global mean temperatures in 2023.

Key Highlights of the Study

• Published In: The study was published in the journal Science.
• Data Analysis: Satellite data from radiation readings from NASA’s Clouds and the Earth’s Radiant Energy System and European Centre for Medium-Range Weather Forecasts (ECMWF) were used. 
  • A complex weather model was generated to get a detailed understanding of the evolution of the global energy budget and cloud cover at different altitudes.
• Objective: To find the source of the missing 0.2 degrees Celsius of warming in the year 2023.
• Findings:
  • Decline in Low- Altitude cloud cover: It fell globally by 1.5 per cent in 2023 compared to average levels continuing a decade-long decline of 1.27 per cent.
    • The sharpest decline in Low- Altitude cloud cover was seen over northern mid-latitude and tropical oceans like the Atlantic likely accounting for the 0.2C of warming.
    • A slight decline in moderate- and high-altitude clouds (which typically trap heat emitted from the surface in the atmosphere) was also observed.
  • Reason for the Decline: The decline is attributed to many causes, that is
    • Global Reduction in Aerosol Pollution: Lower concentrations of anthropogenic aerosols in the atmosphere, especially due to stricter regulations on marine fuel.
    • Natural regional variability, which are variations in the climate system outside of human influence.
    • Climate change induced ocean feedbacks leading to global warming could have also reduced the number of low clouds
  • Consequence of the Decline: 
    • The reduction of cloud cover led to a drop in planetary albedo 
      • 2023 appeared to have the lowest level of albedo since 1940 with approximately 15 per cent of the albedo decline linked to the loss of Arctic snow and sea ice, which are vital for reflecting sunlight.
    • Climate Feedback Loop: The loss of reflective clouds will lead to a positive climate feedback loop whereby it would lead an increased pace of global warming 
    • Warming Effect: Low Altitude clouds reflect more incoming solar radiation then they absorb, thus having a cooling effect on the planet. Its loss will result in more warming.
    • Reduced Rainfall: Tropospheric Clouds hold water that leads to rainfall. The loss of these clouds will also affect the precipitation pattern globally.

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About Low Altitude Clouds

• These are clouds that form below 6,500 feet (2,000 meters)  and are made up of liquid water droplets or supercooled droplets. 
• Reflective: They are highly reflective of the sun’s radiation, which cools the Earth’s surface.
• Characteristics:
• • Composition: Low clouds are made up of more water than high clouds. During cold winter storms, low clouds can contain ice crystals and snow. 
  • Cloud Albedo Forcing: Low Altitude clouds cloud albedo forcing is large and are much thicker than high cirrus clouds and therefore not as transparent which leads to reflection of  much of the solar energy back to space
  • Effect on climate: Low clouds cool the Earth’s surface more than they warm it. However, climate change can affect clouds, and scientists predict that as the Earth warms, there will be fewer clouds to cool it down.