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Subject: Re: Climate change and fish
From: [log in to unmask]
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Wed, 17 Jan 2018 12:11:38 -0500
Content-Type:text/plain
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Chris,

The problem with your suggestion is that measurements of temperature  
(unlike precipitation) are necessarily related to an arbitrary zero.  
Thus, a "1%" change in the numerical value is meaningless.

For example, if the Atlantic Water entering the Barents Sea was to  
warm from 3 to 4 Celsius, it might look like a 33% increase but it  
could just as well be a 5% increase (in Fahrenheit) or even 0.4% (in  
Kelvin). Even if we just used a "modified Celsius" for oceanographic  
purposes, with zero at the freezing point of seawater, rather than  
fresh, the change would be a "mere" 19%. With such a spread of  
numerical values, none of them can convey any understanding.

You could try defining a "biological zero", at which all biological  
activity would shut down, but that is likely to vary from one  
ecosystem to another, which would further complicate interpreting  
percentage changes.

Better to stick to a straightforward, understandable measure (e.g.  
increases in Celsius units) for the simple stuff and then get busy  
with understanding and explaining projections in ecological and  
ecosystem terms. For the Arctic Ocean, that won't be a matter of  
temperature increases so much as the degree of penetration of various  
water masses and the ecosystems found within them, the dominant effect  
of salinity on seawater density once temperatures are around the  
freezing point, the implications of surface mixing and sunlight  
penetration in the absence of ice cover, etc. etc. Temperature change  
is a very crude proxy for all of that and hence one that is best kept  
as simple as possible.


Trevor Kenchington



Quoting Chris Harrod <[log in to unmask]>:

>> <>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>
>            REPLIES WILL BE SENT TO THE FISH-SCI LIST
> <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><
>
> Folks
>
> A quick question. In many climate change projections, temperature  
> changes are reported in C shift from baseline, while precipitation  
> (or discharge) is provided in % terms.
>
> What are peoples' thoughts regarding presenting temperature change  
> as a % - as a means of highlighting those areas where changes are  
> going to be large (e.g. Arctic). I appreciate that giving a C value  
> allows estimated of effects on vital rates  etc.
>
> Cheers
> Chris
>
>
>> <> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><> ><>
> Professor Chris Harrod
> (Fish & Aquatic Ecology)
>
> Email: [log in to unmask]<mailto:[log in to unmask]>
> Twitter: @chris_harrod
> www.harrodlab.net<http://www.harrodlab.net>
> HarrodLab: Fish and Stable Isotope Ecology Laboratory
> Instituto de Ciencias Naturales Alexander von Humboldt,
> Universidad de Antofagasta,
> Avenida Angamos 601, Antofagasta, Chile
> Chile Mobile: +56 9 7399 7792
> Chile Office: +56 55 2637400
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>
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