Short-term Predictions - Climate Change: Identification and Projections - page 123

11.4. Decadal time scale predictions by EBM

Figure 11.3 shows predictions which we made during 2014. The 2013
global temperature was already known for 2013, but not yet for 2014.

HadCRUT4
Predictions
Trend (2000-2013)

1.5

1

0.5

0

1980 1990 2000 2010 2020 2030 2040 2050

Figure 11.4. Short-term predictions

From these predictions, we can distinguish an oscillatory component
resulting from the extrapolation of the effect of the Schwabe cycles. In the
short-term (2020), we predict on average a small drop in temperature, which
may be hidden by internal variability. In the medium-term, there appears to
be no clear upwards trend like that of the decades 1970-2000. In the even
longer term, the projections reach those in Figure 10.3, with their
uncertainties, linked as much to the estimation of climate sensitivities as to
predictions of solar activity.

The projections in Figure 11.4 are based on a collection of models whose
coefficients of climate sensitivity are in the range [0, 2.48] °C , and the total
sensitivity to irradiance in the range [1.9, 29.0] °C/Wm -2 . Since future
temperatures will remain subject to natural and varied fluctuations, it will be
necessary to wait for one or two decades more in order to start seeing the
true figures. And even if one of the above models was “correct”, there is
nothing to guarantee that the causal inputs (solar activity and volcanic
activity) will adhere to their predictions.

At this level, short-term predictions present nothing spectacular: one may
even believe in a simple linear extrapolation using temperatures from the
start of this century. This is not at all the case: if it were, the predictions