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1 NOAA State of the Science Fact Sheet on Ocean Acidification http://nrc.noaa.gov/plans_docs/2008/Ocean_AcidificationFINAL.pdf  

Climate Engineering 

State of the Science FACT SHEET 

Climate engineering, also called geoengineering,refers to deliberate, large-scale manipulation of

Earth’s climate intended to counteract human-caused climate change.

 As a world leader in climate science, NOAA has expertiseto assess the state of the science and the potentialefficacy and consequences of climate engineeringproposals. This Fact Sheet explains the basic science of,but does not endorse, climate engineering.

Why discuss ‘engineering’ the climate?

Some well-established facts and serious global trendsmotivate climate engineering discussions:

•  Increases in atmospheric greenhouse gases(particularly CO2) at rates and to levels notexperienced over at least the past half-million years

•  Very slow (thousands of years) natural removal ofindustrial CO2 from the atmosphere and oceans

•  Ineffective efforts to slow greenhouse gas emissions

•  Observed and projected climate warming andassociated environmental and societal impacts

•  Acidification of ocean surface waters1 by CO2 

Growing interest in potential climate engineering optionsnecessitates a more complete understanding of theproposed actions and their possible impacts. However,scientific research on climate engineering is in its infancy,

with most relevant research published only in the past fewyears. Studies have just begun to explore the potentialenvironmental and societal consequences of any climateengineering proposals.

Two different climate engineering approaches are mostcommonly considered:

•  Removing some CO2  from the atmosphere to reduceits greenhouse effect

•  Increasing the reflection of sunlight away from Earthback to space, thus cooling the planet

This Fact Sheet describes these approaches. It does not

treat the full spectrum of proposals, including capture andstorage of industrially emitted CO2 before it mixes with air.

How might CO2 be deliberately removed from theatmosphere to reduce climate change?

The main greenhouse gas contributing to climate changeover the past century is CO2. Studies have trackedsources of atmospheric CO2  and its accumulation in theatmosphere, ocean and biosphere (as illustrated). CO2 emissions and the rate of atmospheric accumulation havegrown by about a factor of three over the past half century.

Because fossil fuel use dominates other CO2  sourcesreducing those emissions is the most direct way t

influence future atmospheric increases. One class oclimate engineering proposals seeks instead tconcentrate and remove some CO2  from the atmospherand store it on land or in the ocean. Proposals arnumerous, but the main categories are:

•  Adding nutrients, such as iron, to the ocean tenhance the growth of phytoplankton that remove COfrom surface waters (ocean fertilization)

•  Capturing atmospheric CO2  via chemical processeinvolving specially designed solids or liquids

•  Mining and processing silicate or carbonate rocks taccelerate natural chemical weathering processethat involve reaction with CO2 

•  Modifying land ecosystems to store more carbon bincreasing forested areas

•  Turning agricultural wastes that would otherwisdecompose and release CO2  into solid carbo(biochar) or changing farm practices to avoid COrelease from soils (no-till)

Basic challenges involve the scale of potential carboremoval activity. To be effective, the amount of COremoved must be enormous, comparable to the emissionof the global energy industry. Removing dilute CO2  fromthe global atmosphere requires energy, which may bcostly and create additional pollution. Other scientifconcerns include:

•  Effects of fertilizing ocean surface waters on oceaecosystems are poorly understood.

•  “Permanent” storage options may prove unstable anso undermine long-term removal of atmospheric CO2

•  Storage in temporary reservoirs (such as plants thareturn CO2  to the atmosphere when they die) wourequire ongoing management.

•  Depending on the vegetation they replace, foresplanted to absorb CO2 might reflect less sunlight anso undermine the intended climate cooling effects.

Illustrations show sources of CO2 (upward arrows) and its accumulatioin the atmosphere, oceans, and biosphere (downward arrows), gigatons of carbon per year, and large increases from 1960 (at left) t2010 (at right).

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June 2012

How might deliberately reflecting sunlight awayfrom Earth reduce climate change?

Our climate’s energy source is the Sun, but not all sunlightwarms the Earth. About one third is reflected back tospace by the atmosphere (clouds and particles), land(deserts and snow), and ice-covered ocean. A class ofproposals seeks to counter some global warming byincreasing reflection of sunlight (as illustrated). These

include:

•  Placing mirrors between Earth and Sun, either in theatmosphere or in space

•  Injecting reflective particles into the stratosphere, tomimic the process leading to global surface coolingfollowing explosive volcanic eruptions

•  Brightening low-level clouds over oceans by injectingparticles to increase concentrations of smaller, morereflective cloud droplets

Illustration of the main ways sunlight is reflected away from Earth

Scientific understanding of these reflection processes andtheir effects on climate varies. The effect of mirrors can bemore readily estimated, because interactions with otheraspects of the environment are limited. Explosive volcaniceruptions have provided some opportunity to study short-term effects of stratospheric particles on atmospherictemperature (stratospheric warming and surface cooling)and ozone (depletion of the protective stratospheric ozonelayer). Cloud research has revealed complex interactionsbetween particles and clouds, so net effects of injectedparticles on global or local climate are difficult to predict.2 

Other scientific concerns are:

•  Increasing reflection of sunlight does not addressatmospheric CO2  increase and related environmentalimpacts, such as ocean acidification and changes inland and ocean food chains and ecosystems.

•  Atmospheric particles are relatively short-lived (lastinga few days in the lower atmosphere and a few yearsin the stratosphere), so maintaining their brighteningeffect would require ongoing injections.

2 NOAA State of the Science Fact Sheet on Aerosols & Climate

http://nrc.noaa.gov/plans_docs/SOSFactSheet_AerosolsandClimate_October2011.pdf  

•  Once initiated, ceasing actions to increase reflectio

of sunlight could lead to more rapid climate change

than would otherwise have occurred. 

Legal, Ethical and Societal Concerns

In addition to scientific challenges, climate engineerinproposals have serious and complex ethical and legadimensions and raise social, political and economquestions, including:

•  What standards should constrain climate engineerinresearch or dissemination of results that could bused to do harm?

•  If climate engineering would benefit some people anharm others, how could gains and losses be weighed

•  Would it be fair to adopt technologies that involvcommitments by future generations to maintain them?

•  Pursuing climate engineering may undermine efforto reduce emissions or be more resilient to climatchange. Are the resulting avoidable risks justifiable?

•  How can societies and political institutions organiz

themselves to best address such questions?

Currently, no regulatory, legal or ethical framework (sucas those required for the biological and medical sciencesprovides oversight of climate engineering research oimplementation. Internationally, no legal framework existto comprehensively govern climate engineering. Howevecertain international agreements, such as the LondoConvention/Protocol (covering dumping wastes at seahave addressed specific activities, such as oceafertilization and storage of CO2 below the ocean floor.

Because fully controlled experiments (with and without a

intervention) cannot be undertaken in the real world, it difficult to verify that a modification achieves its goal anto gauge risks of unintended, possibly harmfuconsequences. Experience with weather modification, somewhat analogous issue, has demonstrated theschallenges, which are especially relevant to climatengineering.

NOAA Resources and Capabili ties 

NOAA science investigates and informs many compleand controversial environmental issues, such as ozondepletion and ocean acidification. Its research programand scientific integrity policies provide a foundation fo

sound scientific input to decision-making. NOAA scientifexpertise relevant to climate engineering includeatmospheric physics and chemistry, climatologyoceanography, biology, ecology, economics and sociasciences. NOAA participates in international and domestocean fertilization policy discussions.