fredag 21 augusti 2009

Feedback, Sensitivity, Cancellation and Duality

The sensitivity of a mathematical model is a measure of the effect on a certain model output from variation of certain model input data. The sensitivity to errors in data, modeling and computation directly connects to the accuracy of a model. 

Climate sensitivity is primarily concerned with the effect on the global mean temperature from increasing the CO2 concentration in the atmosphere. 

Concerning the climate sensitivity of current climate models, IPCC states:
  • Spread in model climate  sensitivity is a major factor contributing to the range in  projections of future climate changes. 
  • Consequently, differences in climate  sensitivity between models have received close scrutiny in all  four IPCC reports.
  • Climate sensitivity is largely determined  by internal feedback processes that amplify or dampen  the influence of radiative forcing on climate. 
  • (A) To assess the  reliability of model estimates of climate sensitivity, the ability  of climate models to reproduce different climate changes  induced by specific forcings may be evaluated. 
  • (B) An alternative approach, which is followed here,  is to assess the reliability of key climate feedback processes  known to play a critical role in the models’ estimate of climate  sensitivity. 
Here (A) is a reasonable way of testing climate sensitivity, and gives a large spread shown in Fig 10.2, while (B) boils down to 
  • To assess the reliability of model estimates of climate sensitivity, we assess the reliability of key climate feedback processes  known to play a critical role in the models’ estimate of climate sensitivity. 
In other words, assessment of climate model sensitivities, is replaced by assessment of the feedback processes built into the model. But this is an internal check which appears to be circular: You build in a certain feedback process into the model and you then test model sensitivity by testing the validity of the feedback process you have put in. But in most cases you cannot isolate and experimentally test the validity of the feedback process you have put in: If you could directly observe climate sensitivity experimentally, then climate models would serve no purpose. 

But some sensitivities can be observed experimentally, and thus can serve as reliability tests of climate models. This is done in a recent article by Richard Lindzen showing that the radiation sensitivity of current climate models with respect to surface temperature, does not fit with observations, as shown in the above figure with ERBE radiation measurements: Climate models show too small radiation. Something is apparently wrong with the climate models, and there are many things that could be wrong...

In our exploration of the secret of turbulence by computation, we have studied output sensitivity by duality techniques based on solving associated dual linearized problems, and we have found that local exponential turbulent perturbation growth is controled by effects of cancellation. 

In turbulent flow, an important charcteristic of climate atmosphere/ocean circulation,  cancellation means that the worst combination of effects does not occur: Increase in space-time is balanced by decrease in space-time so that the net effect is smaller than worst case. Duality techniques should be able to offer important information on sensitivity also in climate models, but current models lack this capability and there seems to be room for improvement...will cancellation and duality help save humanity?

1 kommentar:

  1. The land based data is manipulated by incorrect "homogenization" based on weather stations affected by urban crawl. There is also selective elimination of weather stations that don't show enough warming. Raw data from some Australian stations in Northern Victoria for example shows no warming in over 100 years. Only satellite measurements are reliable and, as is to be expected, they show no warming since 1998. There is, however, long-term warming of about half a degree per century since the "Little Ice Age" but it can be expected to become about 500 years of long-term cooling before the end of this century if past natural cycles continue.

    However, regardless of any warming, carbon dioxide cannot be the cause as there is no valid physics that can give any reason for such. The infant science of climatology (in which there are few with qualifications in physics) has abused the laws of physics and ignored the prerequisites for such laws to apply.

    Their first fundamental error was to assume that, in the absence of so-called "greenhouse gases" (1% water vapor, 0.04% carbon dioxide and some others) the Earth's surface temperature would have been the same as that about 5Km up into the troposphere. This ignores the effect of gravity which (as has been discussed since the 19th century) forms a stable equilibrium non-zero temperature gradient in every planet's troposphere. Now, in the 21st century, experiments with centrifuges and vortex cooling tubes demonstrate centrifugal force also creating a radial temperature gradient for the same reason that gravity does. Furthermore, a correct understanding of the process of entropy maximization in physics enables us to explain why this happens as gravity acts on molecules between collisions. So there is no need to explain the warmer surface temperature with radiation, and radiation is not the cause thereof.

    The second fundamental error is that, in their unnecessary attempts to explain the fact that the surface temperature is warmer than that 5Km above, climatologists have incorrectly assumed that they can just add together the flux of radiation from the Sun and about double that flux from the colder atmosphere. The latter can have no warming effect what-so-ever on the warmer surface, whilst even the solar radiation does not always raise the existing surface temperature, especially in winter and in the early morning and late afternoon. Once again, we can confirm that radiation can not be compounded like that with a simple experiment. We can measure the temperature to which a single electric bar radiator will raise an object and then see if several such radiators achieve the results that climatologists would like to see. They don't come anywhere near doing so.