Some people raise concerns about global warming and others cite cycles as an explanation for changes but the historical record offers support for both points of view. It does not appear to be purely global warming or necessarily a cycle. To get an accurate reading on any long term warming we have to allow for the possibility of cycles or fluctuations and eliminate their effect on a fit to the data. The results are shown for Jul, the warmest month on average, for Mean Land Temperatures in the northern hemisphere. The only explanation for the data is that both long term effects and short term effects are present.
These fits are just empirical and not based on any particular theory as to what is happening. The fits can be extrapolated to give an estimate of future temperatures. Note that for this plot the temperatures are given in °F while in previous blogs °C was used.
Supplemental: If σ is the standard deviation for the fit one would expect the temperatures to be within 3σ (approximately 0.5 °F) of the solid curve. These are mean values for the month so one would also have to add an additional correction to estimate bounds for the daily highs and lows for a particular location.
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