Global Warming Science -


Hirta’s Sheep are Shrinking


[last update: 2009/07/11]


Another absurd claim about global warming.




From the article: “Thanks to detailed monitoring that began on Hirta in 1986, Coulson and his colleagues could figure out why females in this population are shrinking.



Hirta is in a small archipelago off the northwest coast of Scotland at approximately 57 N, 8 W. The following figure shows the location of Hirta. The closest stations in the NOAA Global Historical Climate Network (GHCN) are indicated as orange dots. The graph to the right shows January – February average temperatures for the average of the two closest stations (Stornoway and Tiree). The graph below the map shows the average temperature anomaly for the 5x5 degree grid (55-65N x 5-10W – indicated by the green rectangle) from the Hadley CRUTEM3 data (used by the IPCC).


Have winters been warming since 1986? Yes. Are these winters exceeding the long-term winter temperature? Generally, no. The pink bands on the temperature graphs below show historical normal temperature range – only a few years in the last 25 years have been above this range.



From the article: “Over the past 25 years, spring has shifted two to three weeks earlier in Northern Europe. In years with shorter winters, more of the small, weak lambs survived. With more sheep competing for food in spring, growth rates slowed among the surviving youngsters.


The following figure shows the average March temperature for the average of Stornoway and Tiree. If the sheep have actually been shrinking due to warmer winters / earlier spring, they must have been expanding in size between the 1950s and 1980s.




From the article: “To parse out what governs body size in such a harsh climate, Coulson and his colleagues started with basic equations that population biologists use to describe how traits change over time. The researchers combined and refined these equations to create a type of bookkeeper’s ledger that mathematically describes all the factors that in theory could cause a trait to vary.


Oops – they forgot a factor in their computer model – insular dwarfism.


Insular dwarfism is the process and condition of the reduction in size of large animals – almost always mammals – when their gene pool is limited to a very small environment, primarily islands. Examples of insular dwarfism in ungulates include the Key Deer in the Florida Keys of the United States and goats in the Juan Fernandez Islands in Chile. []