1. 1.Ammann, C. M., Washington, W. M., Buja, L., & Teng, H. (2010). Climate engineering through artificial enhancement of matural forcings: Magnitudes and implied consequences. Journal of Geophysical Research. 2.McCusker, K. E., Battisti, D. S., & Bitz, C. M. (2012). The Climate Responce to Stratospheric Sulfate Injections and Implications for Adressing Climate Emergencies. Journal of Climate. 3.Trenberth, K. E., & Dai, A. (2007). Effects of Mount Pinatubo volanic eruption on the hydrologic cycle as an analog og geoengineering. Geophysical Research Letters. 4.Clement, A. C., Seager, R., Cane, M. A., & Zebiak, S. E. (1996). An Ocean Dynamical Thermostat. Journal of Climate.  We looked at six different volcanic events, occurring during 1850-2005 that had a discernable climate change associated with them. In historical record.  To examine the simulated climate change, we are using various global climate modeling systems including the CCSM4 model and a compilation of 18 models from the CIMP5 archive. o Climate data used is available through the Earth System Grid (ESG: pcmdi3.llnl.gov).  We are examining the response of observations and models to only the anomalies associated with a volcanic eruption by removing the influences caused by El Nino Southern Oscillation (ENSO), a phenomena that imparts substantial variance on both types of data at interannual timescales, which may mask volcanic responses to individual events.  In order to remove ENSO influences, sea surface temperature (SST) variability was estimated from observational and model data for the time series from the NINO3.4 region. We then regressed these time series against each of the five variables to estimate the influence of ENSO globally and removed this influence by subtracting the NINO3.4-based estimated to find the SST residual. As global climate continues to change it will become more critical to explore possibilities for climate intervention and remediation to counteract anthropogenic influences. One geoengineering possibility proposes to inject reflective aerosol particles into the atmosphere much like a volcanic eruption would. By emulating a volcanic eruption, there would be a decrease in solar radiation and outgoing longwave radiation, lessening the greenhouse effect [1,2,3]. If this is to become a viable option, it is important to recognize first some of the unintended consequences that might arise from adding large amounts of aerosols into the atmosphere. Our main focus throughout this project is to investigate if there is a consistent response of models to major volcanic eruptions during the 20th century. The result of this research will allow us to compare the outputs of models with observations to gain a better understanding of how the climate has reacted to past volcanic eruption and be able to better understand how a geoengineering solution to climate change may interact with our dynamic climate. Climate change has become inevitable. If we were to construct a cooler climate by implementing a geoengineering solution, such as adding aerosols into the atmosphere, it is important that all of the potential consequences are accounted for. If large amounts of atmospheric aerosols can generate El Nino-like conditions, it will be necessary to know this in advance so we do not change the climate in ways that we are unprepared for. We plan to continue this research by completing the following activities: 1.Single forcing experiments 2.Comparison with CMIP3 models 3.Expanding the time series to encompass a larger population of volcanic eruptions 4.Accounting for other phenomena It is imperative to first, and foremost thank my research mentor, Toby Ault. The guidance he has provided has been greatly helpful in sparking my interest in climate science. Justin Wettstein, David Schneider, Clara Deser, and Lorenzo Polvani also provided helpful comments. This work was performed under the auspices of the Spark Pre-college Internship Program. Dr. Rebecca Batchelor provided writing coaching and guidance through the program that is very much appreciated. I would also like to attribute Nancy Wade, Scott Landolt, Rebecca Haacker- Santos, and the rest of the Spark Pre-college Internship Program staff for providing me with this opportunity to explore the field of climate science and work at NCAR as a high school student. *The maps represent the composites (i.e., average anomalies) in the climate fields indicated. These fields were surface temperature, precipitation rate, surface pressure, wind. After a large aerosol injection to the atmosphere (from volcanic or anthropogenic sources), cooling occurs in observations and models, particularly over land in the later. Our findings also suggest that there is a potential for a weak El Nino “mean state” to emerge in the tropical Pacific from anthropogenic aerosol forcing. The models show above average surface temperature anomalies and increased precipitation in the tropical Pacific, conditions that are often associated with El Nino’s impacts. If the mechanism for El Nino generation from aerosol forcing is realistic, it may lead credibility to the “dynamic thermostat” hypothesis [4] for radiatively forced SST anomalies. This hypothesis proposed that zonally symmetric cooling would weaken the east-west gradient of SSTs by cooling the west relatively more than the east, thus triggering El Nino. Fig. 1: El Nino (top) and La Nina (bottom) observational composites* from 1901-2005. Fig. 2: Observational data for the 1991-1992 Mt. Pinatubo eruption. Fig. 3: Observational data for all volcanic eruptions from 1901- 2005. Pinatubo All Events La Nina El Nino Fig. 4: CMIP5 response to the Mt. Pinatubo eruption. Fig. 7: CMIP5 response to all large eruptions. Fig. 6: CMIP5 non-ENSO response to the Mt. Pinatubo eruption. Fig. 5: CMIP5 ENSO response to the Mt. Pinatubo eruption. Fig. 8: CMIP5 ENSO response to all large eruptions. Fig. 9: CMIP5 non-ENSO response to all large eruptions. Pinatubo in CIMP5 (raw) Pinatubo in CIMP5 (ENSO) Pinatubo in CIMP5 (non-ENSO) All Eruptions in CIMP5 (non_ENSO) All Eruptions in CIMP5 (raw) All Eruptions in CIMP5 (ENSO) Surface Pres. Fig. 10: CCSM4 response to the Mt. Pinatubo eruption. Fig. 13: CCSM4 response to all large volcanic eruptions. Fig. 12: CCSM4 non-ENSO response to the Mt. Pinatubo eruption. Fig. 11: CCSM4 ENSO response to the Mt. Pinatubo eruption. Fig. 14: CCSM4 ENSO response to all large volcanic eruptions. Fig. 15: CCSM4 non-ENSO response to all large volcanic eruptions. Pinatubo in CCSM4 (non-ENSO) Pinatubo in CCSM4 (raw) Pinatubo in CCSM4 (ENSO) All Eruptions in CCSM4 (raw) All Eruptions in CCSM4 (non-ENSO) All Eruptions in CCSM4 (ENSO) Surface Pres.