The estimated warming of between 0.30C and 0.60C over the last 100 years is roughly consistent with increased concentrations of greenhouse gases, but it is also within the bounds of natural variability for weather and climate. It cannot be proven to a high degree of confidence that this warming is the result of the increased atmospheric concentrations of greenhouse gases only. There may be an underlying increase or decrease in average temperature from other, as yet undetected, causes also.