Friday, 30 August 2013

A Pacific Reason why Global Warming has Stopped.

An interesting week in climate change science and climate change politics - sometimes a little difficult to distinguish between them!

We have a new paper published in Nature which ties the current hiatus in global-warming to cooling in the eastern equatorial pacific, a sample area covering just 8.2% of the ocean surface. I quote: "Our results show that the current hiatus is part of natural climate variability, tied specifically to a La-NiƱa-like decadal cooling."

We also have another paper, published the same day in Nature Climate Change, seeking to explain the mismatch between observed and estimated warming over the last twenty years, specifically with reference to "some combination of errors in external forcing, model response and internal climate variability".

Judith Curry has examined both of these papers in her blog and I shall be making reference to her important comments on them.

We are also approaching crunch time in the Arctic, with predictions of continuing catastrophic melt by alarmists looking to be increasingly untenable. In fact, 2013 is shaping up to be the year when Arctic ice started to recover at record rates when compared to the all time (well, since 1978 anyway) low recorded in Sept 2012. No doubt, as with the global warming pause, we will soon be hearing from the Arctic alarmists that the 'death spiral' of sea-ice decline was never predicted to be a continuous one and therefore we should expect interruptions (albeit, massive, record breaking ones) in the downward trend.

It looks to me like we are now seeing the beginnings of an acknowledgement by the wider climate science community that natural processes (in particular those mediated by ENSO and PDO cycles - El Nino Southern Oscillation and Pacific Decadal Oscillation, respectively) can have a significant effect on our climate in that they can interrupt rapid predicted CO2 mediated warming to create a 15 year pause and even set the planet off cooling again. However, there seems to be a lack of an accompanying acknowledgement, inherent in this argument, that therefore natural climate forcings have a far more significant role to play in climate change, comparable to, or greater even, than hypothesised anthropogenic influences. Which leads us to the obvious, and the ultimate in climate change heresy, i.e. that 20th/21st Century warming trends have been contributed significantly to by natural influences at play in our ocean/atmosphere coupled climate system, even - perish the thought - that natural forcings have dominated that recent warming trend. We see this reluctance to take the next logical steps very clearly in the following comment taken from the Nature paper referenced above: "Although similar decadal hiatus events may occur in the future, the multi-decadal warming trend is very likely to continue with greenhouse gas increase".

What we basically have at the moment is a PDO in negative phase which is tending to put a lid on world temperatures and even drag them down. ENSO at the present time is fairly neutral, i.e. neither La Nina or El Nino. ENSO is, to a large measure, constrained within the longer period PDO and moderated by this longer period cycle, but ENSO can, and does, flip polarity whilst PDO remains either positive or negative, thereby reinforcing warming/cooling, or tending to act against the prevailing PDO trend. So if we get a strong La Nina soon, this will tend to exacerbate global cooling, and vice versa if ENSO goes into El Nino phase.

Hence, the anthropogenic global warming predicted by climate scientists is, for a variety of reasons, not showing itself and this is placing global warming policy advocates and scientists in a tough position. They may argue that this is a temporary glitch, a minor interruption in an otherwise continual late 20th century/21st century 'catastrophic' warming trend. The problem is, it is neither minor, nor particularly temporary, lasting anywhere between 12 and 20 years, depending on how you look at the figures and which dataset you choose to use. Nor also was it widely predicted, as claimed, by the climate models used by the IPCC, particularly those developed in the 1990s. Even now, a 15 year hiatus in global warming is a very rare occurrence in model runs and let us not forget, it is the climate models, not observations, which still drive current thinking on the threat posed by a hypothetical anthropogenic global warming. Natural variability was, and still is, regarded as minor compared to the effects of man-made CO2 on climate change according to IPCC scientists - though we wait with baited breath for the soon to be published finally completed AR5.

Judith Curry quotes excerpts from the Nature Climate Change paper here. On the subject of the 15 year hiatus starting in 1998, the authors say:

"The inconsistency between observed and simulated global warming is even more striking for temperature trends computed over the past fifteen years (1998–2012). For this period, the observed trend of 0.05 ± 0.08 °C per decade is more than four times smaller than the average simulated trend of 0.21 ± 0.03 °C per decade. The divergence between observed and CMIP5- simulated global warming begins in the early 1990s, as can be seen when comparing observed and simulated running trends from 1970–2012.
The evidence, therefore, indicates that the current generation of climate models (when run as a group, with the CMIP5 prescribed forcings) do not reproduce the observed global warming over the past 20 years, or the slowdown in global warming over the past fifteen years. [S]uch an inconsistency is only expected to occur by chance once in 500 years, if 20-year periods are considered statistically independent."

The authors conclude that some "combination of errors in external forcing, model response and internal climate variability" is to blame for these large discrepancies. They tentatively identify ENSO, volcanic activity and the AMO (Atlantic Multi-Decadal Oscillation) as playing their part, though admit that the amplitude of these natural influences is probably not sufficient to account for the gap between observation and model prediction, inviting the reader to perhaps conclude that the models themselves may be somewhat lacking.

The real eye-opener is the Nature paper which Judith talks about here. By looking at the two separate graphs of simulated 'natural plus anthropogenic' and 'natural internal variability only', in comparison with observations (which the former graph matches closely), she states the following:

"What is mind blowing is Figure 1b, which gives the POGA C simulations (natural internal variability only).   The main  ’fingerprint’ of AGW has been the detection of a separation between climate model runs with natural plus anthropogenic forcing, versus natural variability only.  The detection of AGW has emerged sometime in the late 1970′s , early 1980′s. Compare the temperature increase between 1975-1998 (main warming period in the latter part of the 20th century) for both POGA H and POGA C:
  • POGA H: 0.68C (natural plus anthropogenic)
  • POGA C:  0.4C (natural internal variability only)
I’m not sure how good my eyeball estimates are, and you can pick other start/end dates.  But no matter what, I am coming up with natural internal variability associated accounting for significantly MORE than half of the observed warming."

So, we have an anthropogenic effect, but it is outpaced by natural changes. As a rough calculation, we are looking at natural exceeding AGW by 40%, which is most definitely not the message that has been consistently drilled into us by the IPCC, who have always maintained that natural forcings are not significant and/or are surpassed by man-made climate change.

So it would appear that, as sceptics have maintained all along, climate changes naturally and these natural changes outweigh any man-made influences upon our climate. In particular, ocean currents seem to be driving these changes over multi-decadal periods. Take another step then and ask the question: what is driving the ocean currents? The Sun, our very own star, that superheated ball of plasma 330,000 times as heavy as Earth, 109 times Earth's diameter, just 93 million miles away, is the most likely candidate. Theodor Landscheidt theorised that solar activity and PDO/ENSO were connected. He also predicted what has become known as the Landscheidt Minimum, the current decrease in solar activity, which is calculated to impact upon our climate in the coming decades by sending world temperatures down. Tallbloke's blog gives further info on Lanscheidt's theories here and here and is well worth taking the time to read. In my opinion, climate science is about to move away from the current obsession with CO2 to a more balanced approach involving a holistic assessment of factors affecting climate variability, with the Sun sitting squarely at the top of a pyramid of spreading influences and AGW, at best, relegated to a role on the sidelines, enviously watching the main players.

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