There has been widespread investigation of the drivers of changes in global temperatures. However, there has been remarkably little consideration of the magnitude of the changes to be expected over a period of a few decades or even a century. To address this question, the Holocene records up to 8000 years before present, from several ice cores were examined. The differences in temperatures between all records which are approximately a century apart were determined, after any trends in the data had been removed. The differences were close to normally distributed. The average standard deviation of temperature was 0.98 ± 0.27 °C. This suggests that while some portion of the temperature change observed in the 20th century was probably caused by greenhouse gases, there is a strong likelihood that the major portion was due to natural variations.