Evidence of Causality Between the Atmospheric Concentration Level of Carbon Dioxide and Temperature

Climate change skeptics remain unconvinced that increases in the atmospheric concentration of carbon dioxide (CO₂) has any climate or meteorological implications. In contrast, many climate scientists believe that increases in CO₂ concentration levels do indeed have climate and meteorological consequences but that it is impossible to disentangle these effects from those of other factors. This paper contends that it is possible to assess the effects of CO₂ and other greenhouse gases on weather. This paper explores the relationship between the atmospheric concentration of CO₂ and the dry-bulb temperature using hourly CO₂atmospheric concentration and solar irradiance data from the Mauna Loa Observatory (MLO) in Hawaii.

The starting point of this paper is the recognition that meteorologists do not explicitly take CO₂–induced temperature changes into account when making weather forecasts. The analysis makes use of day-ahead hourly weather forecast data to control for expected weather conditions exclusive of CO₂ considerations. The analysis employs a two-step procedure. In the first step, the issue of functional form is addressed. Using the results of the first step as a base, an autoregressive moving average (ARMA) process is then modeled. The estimation results are consistent with the hypothesis that the hourly CO₂ concentration level has implications for temperature. An out-of-sample forecast is then performed using six months of hourly data. Consistent with the existence of a causal relationship, the inclusion of the CO₂ level as an explanatory variable improves the accuracy of the forecast. The improved forecast is also more accurate than conventional temperature forecasts for the same location.