Climate sceptics and denialists put forward many arguments to support their views that climate change is not a big issue. A core argument has been that warming has stopped over the past ten to fifteen years. Graph after graph that seems to support this position has been published. But the statistical basis of these graphs is very fragile.
This argument confuses the short term effects of weather cycles such as El Nino and La Nina and other factors such as volcanic activity with the long term effects of increasing concentrations of greenhouse gas emissions.
In this article I look at one example of this approach and show how very small changes in the selection of the period of temperature trends can give very different warming trend results. And the very variable temperature data means that presentation of relatively short term trends is simply not statistically valid. Longer time scales are needed to identify underlying trends.