Caldeira Lab Research:Climate Intervention ('Geoengineering')

Transient climate-carbon simulations of planetary engineering

H. Damon Matthews & Ken Caldeira

A study of the effects of geoengineering, intentional human climate modification. A reduction in the amount of solar radiation (insolation) could rapidly mask the effects of global warming without a reduction in CO2 emissions, but the quick fix brings serious danger. An abrupt end to or failure of geoengineering could throw the climate into even greater turmoil, possibly leading to warming rates twenty times those seen today.

Matthews, H.D., and K. Caldeira, Transient climate-carbon simulations of planetary geoengineering, Proceedings of the National Academy of Sciences of the United States of America 104 (24): 9949-9954, 2007.

Changes in global temperature and precipitation: In each model, CO2 was increased from 280 to 880ppm. Geoengineering was implemented in one run of the model but not in the other. Diagrams A and B show the results of such an increase on a non-geoengineered world. B and C show the results when geoengineering is implemented to combat the effects of climate change.

Temperature response to geoengineering implemented at different times: The model also ran simulations where geoengineering was implemented immediately (blue), in 2025 (green), 2050 (orange), 2075 (purple), and not at all (red). Each time the model was run, geoengineering provoked a fast cooling response.

Climate response to an immediate cessation of geoengineering: In models where geoengineering was shut off in 2025 (green), 2050 (orange) and 2075 (purple), a very rapid increase in global temperature was observed, up to 4°C per year in the last model. These kinds of results could take place in the real world if geoengineering experienced an unexpected failure or was forced to be shut off due to unforeseen climate consequences.


Geoengineering (the intentional modification of Earth’s climate) has been proposed as a means of reducing CO2-induced climate warming while greenhouse gas emissions continue. Most proposals involve managing incoming solar radiation such that future greenhouse gas forcing is counteracted by reduced solar forcing. In this study, we assess the transient climate response to geoengineering under a business-as-usual CO2 emissions scenario by using an intermediate-complexity global climate model that includes an interactive carbon cycle. We find that the climate system responds quickly to artificially reduced insolation; hence, there may be little cost to delaying the deployment of geoengineering strategies until such a time as ‘‘dangerous’’ climate change is imminent. Spatial temperature patterns in the geoengineered simulation are comparable with pre industrial temperatures, although this is not true for precipitation. Carbon sinks in the model increase in response to geoengineering. Because geoengineering acts to mask climate warming, there is a direct CO2-driven increase in carbon uptake without an offsetting temperature-driven suppression of carbon sinks. However, this strengthening of carbon sinks, combined with the potential for rapid climate adjustment to changes in solar forcing, leads to serious consequences should geoengineering fail or be stopped abruptly. Such a scenario could lead to very rapid climate change, with warming rates up to 20 times greater than present-day rates. This warming rebound would be larger and more sustained should climate sensitivity prove to be higher than expected. Thus, employing geoengineering schemes with continued carbon emissions could lead to severe risks for the global climate system.