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: http://zebu.uoregon.edu/1998/es202/l12.html
Дата изменения: Thu Feb 12 21:12:21 1998 Дата индексирования: Tue Oct 2 00:27:31 2012 Кодировка: Поисковые слова: п п п п п п п п |
First a return to the Salmon
issue:
This is likely a reflection of where the Salmon are and this is strongly coupled to decadel climate changes in the Alaska-BC-PNW region.
This implies, that at any particular point in this region, over timescales of 50 years, salmon counts/catches will be cyclical in nature.
So, be careful what you are told without being allowed to see the larger picture:
|
Graph shows total salmon catch off the coast of North America (including Alaska). |
Decline of In-River catches which is
frequently used as the "best" indicator for overall salmon decline
in the Columbia River System: ![]() |
Implication is that increases in ocean catch are directly responsible for decreases of in-river catches also shown. |
Looking at more data to find significance or not:
Another Case: US Tornado Frequency:
This is the distribution of verified tornadoes in the American
Midwest from the period of 1953--1993:
Is the apparent recent increase significant?
Again the means are similar so we get
Another Case: Urbanization and the Weather
Does Urbanization produce a microclimate in the sense that urban areas are getting warmer.
Here are some results for Washington DC average Tempearture:
Note that the dispersions are all very similar in these periods. The square root of 120 (number of data samples) = 11.
Let's look at the case for Berkeley CA:
So for Berkeley we have: 14.32-13.67/1.5(.27) = .65/.40 = 1.65 --> still not significant but a lot more significant than the case for Washington DC.
This indicates that Berkeley is a better site for this study than Washington DC since the natural climate variations in DC are more severe and hence the signature of a small effect will be much more difficult to get out of the data.