A time-series analysis of the 20th century climate simulations produced for the IPCC’s AR4

For more than two decades a debate regarding the time-series properties of global and hemispheric temperatures has taken place on the climate change literature and it has hardly been settled at the present time. This paper analyzes the IPCC's AR4 20c3m simulations using modern econometric techniques and provides new evidence to support that global temperatures can be better described as a trend-stationarity process with one-time structural change. As a consequence, the cointegration techniques that have been commonly used in the literature are not adequate and results produced using such techniques should be revised. Furthermore, the analysis of these simulations indicates that the increase in the rate of warming shown by observed and simulated global temperature series since the mid 1970's is produced by external forcing factors that cannot be interpreted as being part of natural variability. As stated in Gay et al. (2009), it can be argued that in terms of Article 2 of the Framework Convention on Climate Change, significant anthropogenic interference with the climate system has already occurred and that current climate models are capable of accurately simulating the response of the climate system, even if it consists in a rapid or abrupt change, to changes in external forcing factors.