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Last week the Intergovernmental panel on climate change (IPCC) issued their latest high profile report on the current understanding of climate change.

Their main conclusion is that there can be little doubt that man is responsible for at least half of the rise in global temperatures since the 1950s, due to man-made greenhouse gases.

As a geophysicist myself, I cannot argue with the science behind the greenhouse effect, which is based on sound physical principles.

To that end, the science behind how greenhouse gases such as carbon dioxide would cause warming of the atmosphere, in my mind, is settled.

But there are areas of the science which cannot be described as anywhere near settled, where there are uncertainties that cannot be easily dismissed.

These uncertainties have been an area that I have focused on over the last few years on this climate blog.

The one area which is perhaps as crucial as any is that of climate model performance, because governments around the world are using climate projections to make long term planning decisions, in particular on future energy generation.

Judge for yourself if this part of the science is settled, from the IPCC report, Section D1:

‘The observed reduction in surface warming over period 1998-2012 is due roughly in equal measure to a reduced trend in radiative forcing and cooling from internal variability, which includes a possible redistribution of heat within the ocean (medium confidence).’

‘There is low confidence in quantifying the role of changes in radiative forcing in causing the reduced warming trend.'

‘There may also be a contribution from forcing inadequacies and, in some models, an overestimate of the response to increase greenhouse gas and other anthropogenic forcing.’

To highlight this area of uncertainty further, in late 2009, I wrote an article which you can read HERE in which I look at the then apparent slowdown in global warming.

In it, I discuss research from the Met Office Hadley Centre.

In the research the authors discuss why they believe a levelling off of temperatures can be expected at times.

The research shows that near zero temperature trends for intervals of a decade or less can be expected due to the model’s internal climate variability.

But crucially, the research rules out zero (temperature) trends for intervals of 15 years or more.

We are now 15 years into the so called ‘pause’ in global temperatures and the research further illustrates that this crucial part of climate science is far from settled, and it’s disappointing that more time wasn’t given to this issue across the media in the days since the report was published.

That said the authors of this report are in little doubt that over the longer term, man is altering our climate by adding greenhouse gases to the atmosphere.

Follow me on twitter @Hudsonweather

Comments

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  • Comment number 65. Posted by ukpahonta

    on 10 Oct 2013 19:04

    #64 newdwr54

    'I'm struggling to find how he reaches this conclusion.'

    Try harder.

    'So the claim that the CMIP5 models "predicted" warming at a rate of about +2C/century between 2000 and mid 2013 appears to be unfounded,'

    We both know that is not his statement but yours.

    'especially considering that the vast majority of that period is actually hind-cast by those models.'

    It would be interesting to see how you bend reality to fit that statement.

    'between 1951-2010 the net climate impact of all the internal variability of the climate system summed to zero degrees change. All the observed warming in that period (0.6 to 0.7C) was the result of human greenhouse gas emissions,'

    How many times have you accused people of cherry picking dates, tsk tsk.

    'the combined influence of natural variability and forcing, while they can exert strong short term and regional influences, are not projected by the IPCC to compete with the positive forcing of greenhouse gases over the longer term.'

    Just like the strong short term warming of the tail end of the last century, hhmm.

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  • Comment number 64. Posted by newdwr54

    on 10 Oct 2013 15:06

    61. ukpahonta

    From the abstract:

    "In particular, from 2000 to 2013.5 a GST plateau is observed while the GCMs predicted a warming rate of about 2°C/ century."

    I'm struggling to find how he reaches this conclusion. The IPCC stated in 2007 that "For the next two decades, a warming of about 0.2°C per decade is projected..." http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-projections-of.html

    The IPCC AR4 *multi-model mean* projection between 2000 and 2013 was close to +0.2C/decade, whereas observed temperatures have been around +0.05C/decade. But the multi-model mean is not itself a projection (much less a prediction). The only reference I can find in the AR5 SPM to the near term CMIP5 model projections is warming of between 0.3 to 0.7C between 2016 and 2035.

    It looks to me as though Scafetta is conflating the AR4 multi-model mean between 2000-2013 with the IPCC AR4 2007 statement regarding "the next two decades" (2007 to 2027) and coming up with a "prediction" of +2C/Century warming between 2000 and mid 2013 in the CMIP5 models. Observed temperatures remained within the range of the IPCC AR4 modelled projections 2000-2013, albeit at the lower end; and the period 2007 to 2027 has obviously not yet been sufficiently observed.

    So the claim that the CMIP5 models "predicted" warming at a rate of about +2C/century between 2000 and mid 2013 appears to be unfounded, especially considering that the vast majority of that period is actually hind-cast by those models.

    Re internal cycles of variability: as the IPCC AR5 report makes clear, the reason why the cycles Scafetta is referring to are not reconstructed in the model projections is because natural internal variability is projected to have much less influence over the mid to long term than the effect of the observed increase in atmospheric greenhouse gas concentrations.

    The AR5 report says (with 66%+ probability) that between 1951-2010 the net climate impact of all the internal variability of the climate system summed to zero degrees change. All the observed warming in that period (0.6 to 0.7C) was the result of human greenhouse gas emissions, and the change would have been considerably higher had it not been for the concurrent release of human aerosol emissions (again, with 66%+ probability).

    Barring a large volcanic eruption, the combined influence of natural variability and forcing, while they can exert strong short term and regional influences, are not projected by the IPCC to compete with the positive forcing of greenhouse gases over the longer term.

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  • Comment number 63. Posted by ukpahonta

    on 8 Oct 2013 18:03

    #62 QV

    'No doubt all of the climate modellers will take note'

    Yeh right, they will just claim that it is a curve fitting exercise or hope that it never gets cited.

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  • Comment number 62. Posted by QuaesoVeritas

    on 8 Oct 2013 11:57

    #61. ukpahonta

    Scafetta validates the IPCC GCM's

    Shouldn't that be "invalidates" ;-)

    It seems very comprehensive, I only wish I had the time and IQ to read it.

    No doubt all of the climate modellers will take note.

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  • Comment number 61. Posted by ukpahonta

    on 8 Oct 2013 07:14

    Scafetta validates the IPCC GCM's

    'These results suggest missing mechanisms and a significant overestimation of the climate sensitivity to the adopted radiative forcings, which is particularly evident in the overestimation of the volcano signatures. On a 163-year period since 1850 only the 1970–2000 warming trend (about 20% of the total period) has been approximately recovered by using known forcings. Thus, the ability of the CMIP5 GCM ensemble mean simulations to project or predict climate change 30 years ahead with any reasonable accuracy is questionable. Indeed, it is possible that the 1970–2000 GCM-data matching could be coincidental and simply due to a fine-tuning calibration of the model parameters to reproduce this period.'
    http://people.duke.edu/~ns2002/pdf/EARTH_1890.pdf

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  • Comment number 60. Posted by ukpahonta

    on 7 Oct 2013 21:05

    Stephen Wilde

    Add this one to your list of resources:

    'Consequently, we have shown that a relatively localized and small-amplitude solar influence on the upper polar atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics on critical processes such as European climate and the breakup of Arctic sea ice [23].
    In particular, it affects the structure of the Rossby wavefield, which is key in determining the trajectory of storm tracks [24]. The configuration of the North Atlantic jet stream is particularly susceptible to changes in forcing.'
    http://iopscience.iop.org/1748-9326/8/4/045001/pdf/1748-9326_8_4_045001.pdf

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  • Comment number 59. Posted by ukpahonta

    on 7 Oct 2013 12:26

    #58 JaimeJ

    Horse to water....

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  • Comment number 58. Posted by JaimeJ

    on 7 Oct 2013 11:33

    #56 ukpahonta

    Did you mean 'You can take the data to the warmist . . . . '?

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  • Comment number 57. Posted by quake

    on 7 Oct 2013 11:32

    newdwr54 has a good point. Over the last 30 years the PDO trend has been negative, PDO has become less positive over this period. I would expect PDO to have had a cooling influence since the 80s then.

    This is just how ENSO works. When an El Nino fades, from peak ENSO back to weakly positive, that has a cooling impact. It doesn't matter that ENSO is still positive over such a period, what matters is that it's falling. The influence on global temperature is directly proportional to the index.

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  • Comment number 56. Posted by ukpahonta

    on 6 Oct 2013 13:02

    You can take a warmist to data but............

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