from: Sarah Raper <sraperatXYZxyz-bremerhaven.de>

subject: Re: tanx

to: Tom Wigley <wigleyatXYZxyz.ucar.edu>

Dear Tom, find the **'s look also a end.

I do this because my emails have a habit of disappearing as I write

them so I use an

editor.

Sarah,

Thanx for the comments. I will revise accordingly. Re 1880, you can

fill me in on this. In the TAR there is a gs(1990) term, I presume is

is the area-corrected melt from 1880 to 1990.

There is also a gu(1990).

In Table 11.17 there are model by model values of g(1990), which the

text on p. 682 implies is gu(1990). The gu/gs difference in 1990 based

on the TAR formula is very small. Both of these are about 2cm.

Just what period this covers is not clear. The p. 682 text doesn't say,

but it does say that T(1990) is from 'the late 19th century'.

Elsewhere, Table 11.10 says that the average GSIC rate of increase over

1910-1990 is 0.3 +/- 0.1 mm/yr. This gives a GSIC sea level rise of 2.4

+/- 0.8 cm over 1910-1990. For the same rate over 1880-1990 the rise

would be 3.3 +/- 1.1 cm. So a good and consistent guess for 1880-1990

is 3 +/- 1 cm. This is probably inconsistent with Table 11.17.

I have never worried about this because the pre 1990 changes that can

be computed from the formulae are incomplete and uncertain.

I will have to be careful about this. Anyhow, I am certainly not

extending

the TAR formula back before 1990. Everything begins at 1990, where I

take t=0. In addition, there is a g(1990) term that I simply add in

order to

get the full melt from (nominally) 1880. The gs/gu thing complicates the

algebra a bit, but what I do is very simple.Bahr, 1996; Bahr, 1997).

** p650 last para 11.2.2 Using these methods,Van de Wal and Wild (2001)

found that contraction of area

reduces the estimated glacier net mass loss over the next 70 years by

15 to 20%

(see also Section 11.5.1.1).

** This is all I can find. It implies to me that for AOGCM glacier melt

predictions

the correction was applied. It simply does not mention (that I can

find) what he

did pre 1990. So best just avoid the issue as you seem to suggest.

Your V0 of around 30cm is good. However, I would like to stick to the

TAR estimate, which is 40cm as explained in the text, for this paper.

**We can go with 40cm if you want, but think about the following. From

the

figure I sent you icecaps account for 30% of the area (12/40*100).

However, they

account for 125% of the volume (.15/.12*100). That's because many many

glaciers are

very small and shallow whereas the icecaps are much larger and

therefore deeper (see

histograms). For around Antarctica and Greenland there is a larger

proportion of

icecaps to glaciers relative to the globe. It doesn't bother me too

much at least 30cm

is just within the range but I'm pretty sure it will turn out to be a

better estimate.

Tom.

****PS Thinking about it in general: I think we should go ahead but I

have still a slight

reservation because it does in fact make the compliment of using his

method which

I dislike very much. Physically it is all wrong. Never mind, though

what I did do at

some point and we could do it is tune our original model to give

similar results, I

found the shape was a bit different. I wonder how it would compare for

the longer times.

Its rather easy to do espically as we know the Vo to use (the same).

*** I think we need to include the Gregory and Oerlemans ref:

Gregory, J.M. and J. Oerlemans, 1998: Simulated future sea level rise

due to glacier melt

based on regionally and seasonally resolved temperature changes.

Nature, 391, 474-6.

This is the official ref for the 'method', prior to the area

correction.

also should include:

Van de Wal, R.S.W. and M. Wild, 2001: Modelling the response of

glaciers to climate

change, applying volume area scaling in combination with a

high-resolution GCM.

IMAUReport R-01-06, Utrecht University, Netherlands.

there must be a better reference than this now....

On 14 Jul 2004, at 17:30, Tom Wigley wrote:

> Sarah,

>

> Thanx for the comments. I will revise accordingly. Re 1880, you can

> fill me in on this. In the TAR there is a gs(1990) term, I presume is

> is the area-corrected melt from 1880 to 1990. There is also a gu(1990).

> In Table 11.17 there are model by model values of g(1990), which the

> text on p. 682 implies is gu(1990). The gu/gs difference in 1990 based

> on the TAR formula is very small. Both of these are about 2cm.

>

> Just what period this covers is not clear. The p. 682 text doesn't say,

> but it does say that T(1990) is from 'the late 19th century'.

>

> Elsewhere, Table 11.10 says that the average GSIC rate of increase over

> 1910-1990 is 0.3 +/- 0.1 mm/yr. This gives a GSIC sea level rise of 2.4

> +/- 0.8 cm over 1910-1990. For the same rate over 1880-1990 the rise

> would be 3.3 +/- 1.1 cm. So a good and consistent guess for 1880-1990

> is 3 +/- 1 cm. This is probably inconsistent with Table 11.17.

>

> I have never worried about this because the pre 1990 changes that can

> be computed from the formulae are incomplete and uncertain.

>

> I will have to be careful about this. Anyhow, I am certainly not

> extending

> the TAR formula back before 1990. Everything begins at 1990, where I

> take t=0. In addition, there is a g(1990) term that I simply add in

> order to

> get the full melt from (nominally) 1880. The gs/gu thing complicates

> the

> algebra a bit, but what I do is very simple.

>

> Your V0 of around 30cm is good. However, I would like to stick to the

> TAR estimate, which is 40cm as explained in the text, for this paper.

>

> Tom.

>

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