Global climate models are accurate enough to be relied upon

Models can accurately reproduce past climate changes: Climate models have successfully simulated many aspects of the climate changes observed during the instrumental period. Most notably, models have reporduced the increase in surface air temperatures remarkably well (1-2). Scientists have also found a high degree of similarity between the simulated and observed evolution of global lower stratospheric temperatures during the past 25 years (3). Good agreement between model projections and observations has likewise been reported for decreases in Arctic Ocean ice cover. As one researcher concluded, “The simulated decreasing trend in average sea ice extent for 1970–1999 (–2.5% per decade) is very similar to observations" (4). In addition, model projections are consistent with observations of changes in ocean heat content since 1960 (5). Models have predicted changes in atmospheric temperatures nearly perfectly: In 1988, Dr. James Hansen predicted future atmospheric temperature changes using several different emissions scenarios. His second scenario most closely resembled the observed pattern of carbon dioxide emissions. Models which employed this scenario predicted that we should have seen .33 degrees Celsius of warming between 1988 and 2005. In actuality, we observed .32 degrees of warming, almost exactly what the models predicted (6). Climate models can accurately simulate important feedbacks: Climate models predict that atmospheric water vapor will increase as the surface warms. Observations have independently confirmed these predictions. Satellite measurements indicate that the total atmospheric water content, which is dominated by water vapor in the lower troposphere, has increased at a rate consistent with model predictions (7-8). Interestingly, upper tropospheric water vapor has also increased during the past two decades (9). Climate model simulations indicate that cloud cover changes will most likely amplify greenhouse gas warming. Observations have confirmed that these predictions are also correct. As Dr. Andrew Dessler noted, “The short-term cloud feedback has a magnitude of 0.54 ± 0.74 watts per square meter per kelvin, meaning that it is likely positive...Calculations of short-term cloud feedback in climate models yield a similar feedback” (10). In a few instances, models have been even more accurate than data: Observations themselves are not without error. In a few cases, model simulations have been even more accurate than data. For example, climate models in the 1990s could not reproduce the full extent of the Northern Hemispheric cooling in the 1950s as indicated by observational data. However, a careful analysis later revealed that the data had been distorted by a change in the way ocean temperatures were measured after World War II (11). In another example, satellite measurements in the early 2000s showed essentially no warming in the middle levels of the atmosphere. More direct measurements by balloons and radiosondes likewise showed no warming there. However, a "tropospheric hot spot" had been predicted by all models clear back to the 1970s. This alleged discrepancy was resolved to the satisfaction of most modelers in 2005, when several researchers documented errors in the sets of observations. For example, the observers had not taken proper account of how instruments in the weather balloons heated up when struck by sunlight. Once these errors were accounted for, it was evident that the middle levels of the atmosphere had indeed been warming up (12). Conclusion: As Dr. Michael Mann remarked, “Current climate models do a remarkably good job of reproducing key features of the actual climate...They also closely reproduce past climate changes. We therefore have good reason to take their predictions of possible future changes in climate seriously” (13). References: http://ipcc.ch... http://150.229.66.66/staff/jma/meehl_additivity.pdf http://atmosdyn.yonsei.ac.kr... http://www.cpom.org... http://www.sciencemag.org... http://pubs.giss.nasa.gov... http://geotest.tamu.edu... http://www.cgd.ucar.edu... http://www.dca.iag.usp.br... http://geotest.tamu.edu... http://www.atmos.colostate.edu... http://www.geo.utexas.edu... Mann, Michael E., and Lee R. Kump. Dire Predictions. New York: Pearson Education, 2008. Print.