Note: This post is superseded by the following post !
The transient climate sensitivity (TCR) is the observed average warming of the earth following a doubling of atmospheric CO2 concentration. Effectively this means the observed average temperature when CO2 levels reach 560 PPM. The current average level of CO2 is 415 PPM and we measure the effective temperature of the earth each month relative to a normalised 30 year average. These average temperature anomalies vary from month to month and year to year due to internal effects like El Nino or Volcanoes. This September was the highest recorded temperature anomaly, but this does not mean that temperatures are suddenly accelerating. Instead the trend regularly varies up or down due to internal cycles like El Nino and volcanic eruptions
The best way to measure the underlying sensitivity of the climate to CO2 therefore is to study long term decadal trends. I do this by using a fixed 3D Icosahedral grid, which has the advantage of both having no geometrical biases, and consistency. The method is described here (3) The decadal average simply integrates all recorded temperature anomalies (1961-1990 baseline) over successive 10 year periods. Hence we get the average global temperature anomaly for the 1960s, 1970s etc. These results are remarkably smooth and integrate over ENSO and other short term affects. Therefore I claim this method isolates the underlying enhanced CO2 greenhouse effect from the noise. Here are the results.
Assuming a continued linear response gives a result of a 2.5C rise in temperatures in 2100 under business as usual. However this is likely an upper limit because if we also consider the full CO2 range by including the NOAA estimates from before the industrial revolution then we see a lower temperature response to increasing CO2 levels. Note that here the CO2 axis scale has been changed slightly.
I conclude that TCR (Climate Sensitivity) is less than or equal to 2.5C. This means that there is no immediate “Climate Emergency” and we have enough time to solve our future energy needs sensibly.