## IPCC AR5 Attribution Statement is wrong

The headline statement on anthropogenic in the Summary for Policy Makers taken from chapter 10 of WG1 reads as follows.

It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period. -

This statement is false because 1951-2010 includes some natural warming from the 60y AMO heat cycle reported by  Tung and Zhou. Fig 10.5 in AR5 shows the  natural internal component as being 0.0±0.05 C. This is wrong because the natural temperature cycle does not average to zero over this period. This is discussed in Natural versus Anthropogenic . My corrected Fig 10.5 is shown below.

The updated Fig 10.5 showing the attribution of warming from 1950 to 2010 where natural internal variation has been  measured by comparing to the 1940 to 2010 period. This represents the net measure of  observed warming because both 1940 and 2010 are peaks of the natural variation which subtracts out when taking the difference. For details see Natural versus Anthropogenic

The residual natural warming present in the 1950-2010 period is 0.2±0.05 C while the observed anthropogenic component is 0.45±0.05 as measured between 1940 to 2010. Both 1940 and 2010 are peaks of the AMO signal which subtract out when taking the difference.  This is why the ‘observed’ global warming trend should be measured from 1940 to 2010 and not from 1950 to 2010.

CMIP5 values for both GHG and the net Anthropogenic signal are now about 50% higher then the observed warming. The correct attribution for the observed warming from 1951 to 2010 is  therefore 75% anthropogenic and 25% natural variability.  CMIP5  sensitivity to CO2 is very likely  50% too strong and overestimates the observed warming once the natural variation is properly included.

A more impartial version of the attribution statement would be

It is very likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together, while about one third was due to natural variation. The best estimate of the human-induced contribution to warming is about 50% greater than the observed warming over this period.

The IPCC will live to regret their selective bias by analysing only the period 1950-2010 .

## Natural versus Anthropogenic

The  natural 60 year heat cycle recently observed in the Atlantic implies that the underlying trend of anthropogenic warming since 1942 has been only ~0.45C. This value results in a derived transient climate response (TCR)  of ~1.5C. The conclusions of the AR5 attribution study now look questionable because they ignore any natural warming component post 1970.

Figure 1. A Fit to HADCRUT4 temperature anomaly data

A new paper Varying planetary heat sink led to global-warming slowdown and acceleration  challenges the AR5 attribution statement that all observed warming can be explained by anthropogenic forcing alone because it shows clear evidence of a natural 60 year ocean heat cycle. This cycle is also evident in the global temperature data – see A 60 year oscillation. A long discussion on this paper can also be seen at Judith Curry’s blog.

Figure 10.5 in the AR5 attribution chapter is based on model comparisons from 1951 to 2010 is now looking rather unlikely because this result leaves no room for any natural component to warming, as shown below.

Fig 10.5 from AR5. ANT is the net anthropogenic forcing. I do not understand how the ANT errors get smaller after adding GHG and OA together !

The new evidence of a significant oceanic warming and cooling cycle means that between 1950 and 2010 anything up to 50% of the rise in observed temperature was actually due to the warming phase of the 60y cycle. The error bars on the ‘ANT’ component in figure 10.5 are just too small to allow for this. If this is the case how can we best estimate the underlying anthropogenic component?

The fit to the H4 data in Figure 1 is based on the assumption of a logarithmic dependence on CO2 forcing and temperature response. The (transient) temperature response includes climate feedbacks and is to be measured. The CO2 forcing is given by $\Delta{S} = 5.3\ln{\frac{C}{C_0}}$ which is derived in Radiative Forcing of CO2 and includes a 60y harmonic cycle which was previously identified  as described in the post “A 60 year oscillation in Global Temperature data and possible explanations” .

The true anthropogenic component of warming can be identified by subtracting off the natural warming/cooling cycle. The peaks of the oscillation occur both in 1942 and 2008 so the rise in temperature between these two dates should measure the underlying human induced CO2 warming.

 Date Anomaly (degC) CO2 level (ppm) 1942 -0.01 ± 0.01 308 2008 0.44 ± 0.01 378

Now assuming that this now represents  the underlying anthropogenic warming between 1942 and 2008, we can measure a value for TCR as follows

$0.45 = const \times \ln{\frac{378}{308}} \implies const = 2.2$

Therefore

$TCR = 2.2\ln{2} = 1.5 C$

with an error of about 0.1 C

Conclusion:  The new paper by Chen and Tung provides independent evidence for a global 60 year warming and cooling cycle due to natural variations in AMOC. The IPCC attribution statement is based on model fingerprint evidence that all warming since 1950 can be explained by AGW. However this measured warming must contain a component from the AMOC warming cycle from 1970 to 2000. Only by comparing dates at similar positions in the cycle can the true anthropogenic component be identified.  We choose 1942 and 2008 as the peaks in this cycle to show a net warming of 0.45±0.2 C. CO2 levels rose by 70 ppm between those two dates. This is then used to derive from observations a value for  TCR = 1.5 ± 0.1 C.

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## Jet Stream Blues – the movie.

These are the two animations I made of the UK winter storms based on charts from meteociel.fr and then synchronised with my calculations of the tidal forces.

First the Jet Stream.

This animation is of Jet Stream data over Europe and North Atlantic originating from meteociel.fr. It is overlaid with calculations of the tractional tidal forces updated every 2 hours. This animation covers the period 1 December 2013 until 13th February 2014. Do strong atmospheric tidal forces influence Jet stream flows ?

Now the storms themselves tracking across the Atlantic.

This animations shows the development and progression of a series of storms to hit the UK over winter 2013/14. The weather maps are curtesy of meteociel.fr and show pressure isobars coloured effectively by air temperature. Overlaid with arrows are the vector “tractional” forces acting on the atmosphere/oceans due to lunar/solar tides. The tides are updated every 2 hours with the rotation of the  earth rotates. The weather maps update every 12 hours. You can stop the animation to step through each storm.  The storms December 5/6 and January 3/6 in particular show evidence of being influenced by atmospheric tides.

Apologies in advance for the sound tracks!   You can always mute them !

Posted in AGW, Meteorology, Physics, Science | Tagged , | 2 Comments