One proposed solution the solve the climate crisis is solar geoengineering or reflecting the Sun's energy back into space for Earth to cool. However, new research suggests that solar geoengineering may be ineffective if greenhouse house gas emissions continue to increase.
The study published in the journal Proceedings of the National Academy of Sciences describes the results of climate simulations. According to Professor Tapio Schneider from Caltech and NASA's Jet Propulsion Laboratory, solar geoengineering received attention because of available technology.
There are also governance and ethical questions about controlling the Earth's thermostat, said Schneider. Moreover, the simulations revealed that the method is not a long-term solution to global warming if greenhouse gas (GHG) emissions continually increase in the next 100 years.
Earth's climate primarily depends on radiation levels at the top of the atmosphere (TOA). Increased GHG levels make the TOA weaker due to solar radiative energy and make the planet warmer. "Solar geoengineering attempts to short-circuit this process by artificially reducing the amount of solar radiation absorbed in the climate system," the authors wrote.
Alongside Colleen Kaul and Kyle Pressel from the Pacific Northwest National Laboratories, they developed high-resolution simulations of stratocumulus clouds. Due to greenhouse gases, clouds have become thinner. If solar geoengineering is sustained for more than a century, wrote the researchers, the stratocumulus clouds would eventually break up and trigger "triggering strong, and possibly difficult to reverse," warming of up to 10 degrees Fahrenheit.
While solar geoengineering seems like an efficient solution, it may only be effective in the short term because it "ignores the bigger picture of how clouds work," said the team. Subtropical marine stratocumulus clouds lower the planet's surface temperature not only by reflecting sunlight to space. They also radiate infrared radiation upward the down to the surface in a process called longwave cooling. The cooling process also explains why areas near tropical oceans have cooler temperatures.
GHGs like carbon dioxide blocks the radiation from moving upward and could eventually cause stratocumulus clouds to break apart. The simulations also paint a picture of what happened on Earth when the Sun was less powerful yet the planet remained warm.
The Need to Reduce GHG Emissions
Current efforts of solar geoengineering include the Safe Climate Research Initiative headed by the non-profit organization SilverLining and in partnership with other organizations and universities for research. The Australian government also has its decarbonization program using marine cloud brightening or helping clouds become more reflective with salt particles from sprayed ocean water.
More importantly, current GHG emissions trends will continue to damage the climate with our without solar engineering methods. "Even with solar geoengineering," the team wrote, "strong global warming can occur if CO2 continues to accumulate in the atmosphere to reach concentrations more than four times today's." What researchers have yet to determine is at what level of carbon dioxide concentrations will lead to the breakup of the stratocumulus cloud.
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