Context: Scientists are experimenting with an idea to fight global warming — brightening up marine clouds by aerosol sprays so that they reflect more sunlight back into the atmosphere.
About Marine Cloud Brightening
- Marine Cloud Brightening Program involves atmospheric scientists and experts collaborating to study how aerosols affect clouds.
- It is a programme of the Department of Atmospheric Sciences, University of Washington, USA
Objective: To understand these interactions and explore the feasibility of reducing climate warming by enhancing sunlight reflection from marine clouds.
Technique: In clean oceanic air, clouds mostly form from sulfates and sea salt crystals, which are not abundant. This results in larger droplets that reflect less light.
- Marine cloud brightening (MCB) aims to increase the brightness of marine clouds by enhancing their reflectivity. It achieves this by releasing tiny sea water droplets into the atmosphere using water cannons or special ships.
- When these droplets evaporate, they leave behind salt particles. These particles act as nuclei for cloud formation, leading to denser and brighter clouds.
Significance of Aerosol-Cloud Interactions:
- Clouds reflect sunlight, cooling temperatures locally and globally.
- Aerosol particles, from natural and human sources, can brighten clouds, enhancing sunlight reflection and cooling the Earth's climate.
- Changes in cloud cover or sunlight reflection can influence climate dynamics significantly.
Role of Aerosol
- Aerosols from both natural sources (like biological emissions and sea spray) and human activities (such as burning fossil fuels) mix with low clouds, especially over the ocean, brightening them and thereby increase albedo. This in turn leads to cooling of climate.
- Uncertainty remains about the overall cooling effect of aerosols on the climate.
- Aerosol air pollution has made the planet about 0.7° F (0.4 °C) cooler than it otherwise would be, according to the 2021 report by the Intergovernmental Panel on Climate Change (IPCC). For comparison, greenhouse gas emissions have added 2.7°F (1.5°C) of warming.
Aerosol and Precipitation
- Aerosols serve as cloud condensation nuclei (CCN), providing surfaces on which water vapor can condense to form cloud droplets.
- The presence of aerosols affects cloud properties such as droplet size, number, and distribution, which in turn influence precipitation formation.
- Effects on Cloud Dynamics:
- Increased aerosol concentrations can lead to the formation of a larger number of smaller cloud droplets, altering cloud dynamics.
- Smaller droplets may reduce the efficiency of raindrop formation and growth, potentially delaying or suppressing precipitation.
- Precipitation Enhancement or Suppression:
- In some cases, aerosols can enhance precipitation by increasing the number of cloud droplets and promoting coalescence and raindrop formation.
- However, in polluted conditions with high aerosol concentrations, clouds may exhibit reduced precipitation efficiency, leading to suppressed rainfall.
Potential Acceleration of Climate Warming:
- Reductions in atmospheric aerosols since 2010 may have accelerated global warming.
- Recent declines in particulate pollution emissions from ships, coinciding with rising ocean surface and global temperatures, emphasize the need to understand these effects.
Understanding Marine Cloud Brightening (MCB):
- MCB proposes using sea salt particles to brighten clouds over the ocean, reducing climate warming.
- Scientific studies suggest that specific aerosols can significantly increase cloud reflectivity.
- Sea salt particles would be sprayed from ships into low-lying clouds, remaining in the atmosphere for a few days within localized areas.
Uncertainties and Considerations:
- Specific regions of the ocean may be more suitable for MCB, but the extent of brightening and its effectiveness in different regions are uncertain.
- Implementation decisions, such as which areas to brighten and to what extent, will determine the climate cooling achieved and its broader impacts.
- Changes in clouds induced by MCB and pollution aerosols can affect atmospheric circulation, weather patterns, and precipitation in both local and distant regions.
Critical Aspects and Research Needs:
- Improving understanding of MCB and aerosol effects is crucial for projecting long-distance effects and associated risks.
- Further research is needed to assess the feasibility, potential consequences, and optimal implementation strategies of MCB in addressing climate change.