Has Global Warming Stopped?

Skeptical Science stated that Phil Jones was misquoted by an article in the Daily Mail which said that, “There has been no global warming since 1995.” In order to check this statement I have analysed the current temperature data from NASA GISS and HadCRUT3 as shown below.

NASA GISS Data Compared with Hansen (2006)

The NASA GISS Land-Ocean data up to December 2009 are shown in Figure 1. They are compared with the global warming models presented by Hansen (2006).

 

Figure 1: Scenarios A, B and C Compared with Measured NASA GISS Land-Ocean Temperature Data (after Hansen, 2006)

The blue line in Figure 1 denotes the NASA GISS Land-Ocean data and Scenarios A, B and C describe various CO₂ emission outcomes. Scenarios A and C are upper and lower bounds. Scenario A is “on the high side of reality” with an exponential increase in emissions. Scenario C has “a drastic curtailment of emissions”, with no increase in emissions after 2000. Scenario B is described as “most plausible” which is expected to be closest to reality. The original diagram can be found in Hansen (2006).

It is evident from Figure 1 that the best fit for actual temperature measurements is currently the emissions-held-at-year-2000-level Scenario C. This suggests that global warming has slowed down significantly when compared with the “most plausible” prediction Scenario B.

It is also worth noting that we are currently at the lower end of the range of estimated temperatures for the Holocene and the prior interglacial period. These occurred without human intervention.

HadCRUT3 Compared with IPCC AR4

The above comparison based on Hansen (2006) uses relatively old climate models. Therefore, I have compared current HadCRUT3 temperature data with the latest IPPC AR4 (2007) models in Figure 2.

Figure 2: IPCC Scenarios A1B, A2 & B1 Compared with Measured HadCRUT3 Temperature Data (after AR4, 2007)

Figure 2 is based on IPCC AR4 Figure TS.26, which is not easily assimilated. Nevertheless, I have added the HadCRUT3 data as blue dots. The black dots in the original diagram appear to be HadCRUT3 data but are slightly misaligned. Therefore, I offset the HadCRUT3 data by adding 0.018°C to achieve a reasonable fit with the individual data points shown in AR4. The blue line with white dots is my offset version of the smoothed HadCRUT3 data. The smoothing was achieved by using the 21-point binomial filter suggested by the Hadley Centre.

It is evident from Figure 2 that my smoothed curve gives an excellent fit with observed data presented as the solid black line in AR4.

The observed temperature trends in Figure 2 are significantly below the “likely” warming scenarios presented in AR4. Indeed, the current trend is similar to the emissions-held-at-year-2000-level scenario.

Conclusions

Two comparisons are presented that compare NASA GISS Land-Ocean data and HadCRUT3 data with their respective temperature simulation models. The following conclusions are offered from these comparisons:

1. Observed temperatures are significantly below the “most plausible” or “likely” high emissions scenarios. Instead, they are on a trajectory that is similar to the emissions-held-at-year-2000-level scenarios.
2. Current temperatures are at the lower end of the range of estimated temperatures for the Holocene and the prior interglacial period. These temperatures occurred without human intervention.

In summary, global warming may not have stopped but it is certainly following a trajectory that is much lower than that predicted by computer models.

Notwithstanding the above, it should be noted that time period for the comparison of actual temperature measurements with those predicted by computer models is still relatively short. Hansen (2006) suggests that we could expect reasonable results for distinction between the scenarios and useful comparison with the real world by 2015.