Sun dimming dangers

Solar radiation modification: NOAA State of the Science factsheet

National Oceanic and Atmospheric Administration

Part of the United States Department of Commerce, headquartered in Silver Spring, Maryland.

SRM deployments large enough to temporarily offset climate change impacts could have substantial risks and unintended and unexpected consequences.

NOAA is one of the lead federal research agencies investigating the Earth system, including the planet’s radiative balance, the global carbon cycle, and the chemistry and composition of the atmosphere.

Side effects of SRM are driven by

Complex chemical, radiative, and dynamical interactions,

such as changes to the hydrologic cycle and clouds,

or effects on ecosystems,

agricultural production,

Impacts on the protective stratospheric ozone layer

Stratospheric aerosol injection, impacts stratospheric ozone

Either by direct injection or by injection of a precursor gas (such as sulfur dioxide, SO2) that would subsequently react in the stratosphere to form aerosols.

SO3 + H2O – H2SO4

More likely in the presence of O3 (ozone)

Proposed aerosol types include sulfate, calcium carbonate, and diamond dust.

The ozone layer is a region in the Earth's stratosphere that contains a high concentration of ozone (O₃) and plays a crucial role in absorbing most of the Sun's harmful ultraviolet (UV) radiation.

Marine cloud brightening, alterations to the El Niño Southern Oscillation

These changes in the seasonal climate of the world's biggest ocean have a cascade of global side effects.

Potential risks to human health and well-being,

and to ecosystems

Green House Gas induced warming and Solar Radiation Management induced cooling are different physical mechanisms;

therefore, SRM would not simply undo GHG-induced warming

and cannot reverse all climate changes everywhere.

Some regions could experience cooler or wetter conditions, and others warmer or drier conditions, compared to a climate without SRM.

In addition, ocean acidification will persist unabated if GHG emissions continue.

SRM deployments large enough to temporarily offset climate change impacts could have substantial risks and unintended and unexpected consequences.

Aerosols are removed from the atmosphere by natural processes on timescales of a few years in the stratosphere.

Legal and societal issues

SRM deployment could also add significant geopolitical risks.

This uneven distribution of benefits and negative consequences introduces potentially significant justice and geopolitical concerns.

Substantial knowledge gaps and uncertainties exist in many critical areas of SRM research, particularly related to the social sciences.

Many of the processes most important for understanding SRM approaches—such as those that control the formation of clouds and aerosols—are among the most uncertain components of the climate system.

These methods have the potential to lower surface temperatures more quickly than carbon dioxide removal (CDR) methods … while posing other risks still to be understood.