Reliable estimates of uncertainty are arguably more important than the actual value being quoted. I recently came across a classic example in astronomy.
From the late 1920s, estimates have been published for the ‘Hubble Constant’ – a measure of how fast the Universe is expanding. It is named after Edwin Hubble who first made the measurements required. Simply, Hubble’s Constant relates the distance to a distant galaxy to how fast it is moving away from us:
v = H0 d
where the velocity (
v) is measured relatively easily using the ‘redshift‘. The distance (
d) is much harder to measure, producing uncertainty in the estimate of Hubble’s Constant (
When Robert Kirschner examined how the estimated value of
H0 had changed with the date of the scientific publication, he found that the early estimates tended to be far too large, but more importantly that the uncertainties were vastly underestimated (see Figure). A modern estimate of
H0 is around 70 km/s/Mpc.
In climate we try and measure the climate sensitivity – a similar constant relating the equilibrium global temperature increase to a change in radiative forcing, and its associated uncertainty. We should continue to remember that estimating the uncertainty can be more important than the central value we obtain.
It may also be interesting to examine how the estimates (and uncertainty) in climate sensitivity have changed over time, since it was first measured in 1896 by Arrhenius.