Frequency dependent climate sensitivity

Nicola Scafetta published another paper today, confirming the period dependency of climate sensitivity. (I would have loved to write this, but he attributes the original idea to a book chapter by Wigley in 1988, so its not original anyway.)

In his words, climate sensitivity is frequency dependent:

However, the multiple linear regression analysis is not optimal because the parameters ki and τi might be time-dependent and, in such a case, keeping them constant would yield serious systematic errors in the evaluation of the parameters ki . Moreover, climate models predict that the climate sensitivity to cyclical forcing increases at lower frequencies because of the strong frequency-dependent damping effect of ocean thermal inertia [Wigley, 1988; Foukal et al., 2004].

When the signal is properly decomposed, solar forcing is significantly stronger at longer periods of oscillation:

In fact, the actual climate response to cyclical forcing is stronger at lower frequencies because the damping effect of the ocean inertia is weaker at lower frequencies [Wigley 1988, table 1]. This frequency dependence arises because the system is typically not in thermodynamic equilibrium. The ratio Z8 /Z7 = 1.55 ±0.55 is consistent with that between the damping factors for 20 and 10 year periodicities η20 /η10 ≈ 1.45 indicated by the Wigley’s model [1988, table 1]. Wigley’s model also predicts a response-lag of 2.5-2.8 years for a 20 year periodicity.

He concludes with the omitted factors in climate models, without which it is not possible to determine the magnitude of natural variation, above which the AGW signal could rise.

As Lean [2005] noted, the models might be inadequate: (1) in their parameterizations of climate feedbacks and atmosphere-ocean coupling; (2) in their neglect of indirect response by the stratosphere and of possible additional climate effects linked to solar magnetic field, UV radiation, solar flares and cosmic ray intensity modulations; (3) there might be other possible natural amplification mechanisms deriving from internal modes of climate variability which are not included in the models. All the above mechanisms would be automatically considered and indirectly included in our phenomenological approach.

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0 thoughts on “Frequency dependent climate sensitivity

  1. This actually seems to be a rather old paper, from 2005, however it is certainly the case that Scafetta continues to draw attention to this point, which is often overlooked. This relates intimately to the difference between “equilibrium sensitivity” and the “transient sensitivity”. Basically it manifests with periodic forcings as essentially a low pass filter, with a step change in forcing as a change in temperature which asymptotes to the final change at some indefinite point in the future, starting relatively rapidly and then slowing down, and with sudden and temporary forcings as a way of prolonging the effect.

    I recently wrote that, at t=infinity, the “sensitivity” should be about 3 degrees C for doubling CO2:

    http://devoidofnulls.wordpress.com/2010/05/26/timescales-special-cases-limitations-etc/

    At least with a comparison involving a shut off sun.

    Interestingly, the sensitivity on more realistic timescales is clearly much lower. If you look at the response to volcanic eruptions, a high sensitivity on short timescales would mean that, if two large eruptions happened in rapid succession, the effects of one on climate would not fully dissipate before the next eruption, which would produce a longer term dip in temperature, rather than the sudden drops an slow recoveries associated with any sensitivity to one eruption (albeit larger sensitivities demand slower recoveries, and ever so slightly sharper drops). It turns out that Krakatoa and Katmai (1883 and 1912) offer such a case, but the temperature record does not show any compounding, indeed the temperature spikes are barely visible at all.

    • I see what you mean. Clearly he is allowing more complex frequency dependent filtering, ie frequency dependent amplification, but that’s not shown here, and probably over-reaching on the data.

    • I should note that in the shut off sun case, shortwave feedback from ice, clouds, etc, is irrelevant for the obvious reason that there is no sunlight to reflect, and the long wave feedback must be positive because the water vapor and clouds and even CO2 when it gets cold enough, don’t stay in the air when it gets too cold, since the maximum amount of WV (or any gas) the atmosphere can hold is bounded by the temperature and approaches zero at sufficiently cold temperatures. They don’t have to go up with increases in temp but they do have to go down with sufficient decreases.

  2. This actually seems to be a rather old paper, from 2005, however it is certainly the case that Scafetta continues to draw attention to this point, which is often overlooked. This relates intimately to the difference between “equilibrium sensitivity” and the “transient sensitivity”. Basically it manifests with periodic forcings as essentially a low pass filter, with a step change in forcing as a change in temperature which asymptotes to the final change at some indefinite point in the future, starting relatively rapidly and then slowing down, and with sudden and temporary forcings as a way of prolonging the effect.I recently wrote that, at t=infinity, the “sensitivity” should be about 3 degrees C for doubling CO2:http://devoidofnulls.wordpress.com/2010/05/26/t…At least with a comparison involving a shut off sun.Interestingly, the sensitivity on more realistic timescales is clearly much lower. If you look at the response to volcanic eruptions, a high sensitivity on short timescales would mean that, if two large eruptions happened in rapid succession, the effects of one on climate would not fully dissipate before the next eruption, which would produce a longer term dip in temperature, rather than the sudden drops an slow recoveries associated with any sensitivity to one eruption (albeit larger sensitivities demand slower recoveries, and ever so slightly sharper drops). It turns out that Krakatoa and Katmai (1883 and 1912) offer such a case, but the temperature record does not show any compounding, indeed the temperature spikes are barely visible at all.

  3. This actually seems to be a rather old paper, from 2005, however it is certainly the case that Scafetta continues to draw attention to this point, which is often overlooked. This relates intimately to the difference between “equilibrium sensitivity” and the “transient sensitivity”. Basically it manifests with periodic forcings as essentially a low pass filter, with a step change in forcing as a change in temperature which asymptotes to the final change at some indefinite point in the future, starting relatively rapidly and then slowing down, and with sudden and temporary forcings as a way of prolonging the effect.I recently wrote that, at t=infinity, the “sensitivity” should be about 3 degrees C for doubling CO2:http://devoidofnulls.wordpress.com/2010/05/26/t…At least with a comparison involving a shut off sun.Interestingly, the sensitivity on more realistic timescales is clearly much lower. If you look at the response to volcanic eruptions, a high sensitivity on short timescales would mean that, if two large eruptions happened in rapid succession, the effects of one on climate would not fully dissipate before the next eruption, which would produce a longer term dip in temperature, rather than the sudden drops an slow recoveries associated with any sensitivity to one eruption (albeit larger sensitivities demand slower recoveries, and ever so slightly sharper drops). It turns out that Krakatoa and Katmai (1883 and 1912) offer such a case, but the temperature record does not show any compounding, indeed the temperature spikes are barely visible at all.

  4. I see what you mean. Clearly he is allowing more complex frequency dependent filtering, ie frequency dependent amplification, but that's not shown here, and probably over-reaching on the data.

  5. I should note that in the shut off sun case, shortwave feedback from ice, clouds, etc, is irrelevant for the obvious reason that there is no sunlight to reflect, and the long wave feedback must be positive because the water vapor and clouds and even CO2 when it gets cold enough, don't stay in the air when it gets too cold, since the maximum amount of WV (or any gas) the atmosphere can hold is bounded by the temperature and approaches zero at sufficiently cold temperatures. They don't have to go up with increases in temp but they do have to go down with sufficient decreases.

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