Re: [asa] Bacterial Gene May Affect Climate And Weather

On Feb 21, 2007, at 8:54 PM, Bill Hamilton wrote:

> Rich is right, Janice. In addition to the points Rich makes below,
> a good model developer will constantly test his model against real
> data to find where its predictions deviate from actual data. Once
> the reasons for the deviation are understood, the model can be
> improved to reduce discrepancies from actual data. Thus the model
> does not serve as a backup for the data, but its development cycle
> is intimately connected with the real data. One question a
> policymaker can ask to ascertain whether due diligence is being
> given to model development, is "Has the model's performance
> improved over time?" The answer for climate models appears to be
> yes, although obviously improvements can still be made.
>

Here's an example of the interaction between theory, data, and models
from tomorrow's Nature:

> So how exactly does water underneath an ice sheet affect ice
> dynamics? As ice flows over a lake, the friction at its base
> vanishes and its speed increases (see Fig. 1). Furthermore, the
> freezing of lake water on the underside of the ice sheet adds
> thermal energy to the basal ice. This prevents the ice from
> freezing onto the bedrock when it hits the ground again, and also
> allows faster flow, as warm ice is much softer than cold ice.
> Nevertheless, for most of the subglacial lakes discovered so far,
> the surrounding ice apparently buttresses the ice over the lake and
> prevents faster flow. Bell et al. suggest that the location of the
> Recovery lakes at the onset of a fast-flowing ice stream provides
> the first evidence that subglacial hydrology could be responsible
> for the initiation of an ice stream, either by changing the ice
> sheet's basal thermal regime or by introducing water into the path
> of the ice stream through periodic drainage events.
>
> If this proves to be the case, it would substantially change our
> understanding of the effect of subglacial lakes on ice-sheet
> stability. It indicates that basal hydrology needs to be accounted
> for in numerical models of ice-sheet motion because it has the
> potential to rapidly induce fast flow. The recent sudden
> acceleration of ice streams in Greenland6, 7, and its resultant
> effect on the mass balance of the Greenland ice sheet8, underscores
> the importance of understanding the dynamics of ice-sheet response
> to climatic change.
and

> The Recovery subglacial lakes capture water from a large area,
> effectively concentrating the energy from basal melting and re-
> releasing it where it can have a significant impact on ice flow
> through either basal accretion or catastrophic drainage.
> Contributing 35 gigatons per year of ice to the global oceans11,
> the Recovery subglacial lakes and the associated Recovery ice
> stream tributaries have the potential greatly to affect the
> drainage of the East Antarctic ice sheet and its influence on sea
> level rise in the near future. Subglacial lakes and the associated
> hydrologic systems are crucial components in the dynamic evolution
> of ice sheets and need to be incorporated into ice-sheet models
> that are used for climate predictions.

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Received on Wed Feb 21 23:52:32 2007