Ireland, the Atlantic, and Temperature

Today we are traveling to island of Ireland and how it is affected by the Atlantic Ocean that surrounds it. The Atlantic’s role in a discussion of Ireland will become evident.
Ireland is known to be warm, wet, and green. Ireland has a maritime climate, and is downwind of the ocean it is settled within. In this scenario, the temperature of an island is related to the temperature of the ocean. Warm air comes off the water during winter, so it keeps the mild temperatures it is known for.
Despite similarities, Dublin, Ireland is an average of 4.3 degrees C (7.7 F) warmer than Seattle, Washington, a city of comparable maritime climate. Why? Today’s article, “The influence of ocean variations on the climate of Ireland” by G.D. McCarthy, E. Gleeson and S. Walsh, published in August 2015 in Weather, discusses just that.  It has been suggested that ocean heat transport–the movement of warm conditions through ocean waters–is the cause of this. However, this view is somewhat oversimplified. Another view suggests that wind becomes more of a factor. In actuality, in a situation like this, both atmospheric and oceanographic factors are important, and the two are not easily separable.
A rare cloud-free image of Ireland by satellite. Image credit: NASA Earth Observatory.
A rare cloud-free image of Ireland by satellite. Image credit: NASA Earth Observatory.
One way to tell the influence of something is to ask ‘what if it went away?’. If the North Atlantic stopped circulating the way it does, what would happen to the temperature of Ireland. Studies suggest this could drop the temperature by 6 degrees C (10.8 F). This is incredibly unlikely to happen, but records indicate that there is multidecadal variability in temperature. Multidecadal variability is a fancy way of saying that things change over several decades. In this case, the variability of interest is the Atlantic Multidecadal Oscillation, or AMO. Based on the records we have so far, the variability is about 0.5 degrees C (1 F) of change over the course of sixty years. That may not sound like much of a change in temperature, but to scientists, it is very much of note. Looking at the sea-surface temperature, there is an upward trend as would be expected from anthropogenic (human-origin) causes, but if you look past that, there is also the natural up and down of the AMO. Positive AMOs give warmer temperatures, such as in the 1940s and 1990s, and negative AMOs are associated with colder temperatures, in the 1970s, possibly with another one starting now.
From the middle of the 1940s to the middle of the 1970s, Ireland’s temperature trended down 0.1 degrees C (around 0.2 F) every decade, a rapid change. This has a striking correlation to what the AMO was doing at the time; the shift in temperatures between Ireland and the AMO are nearly exact. The logical conclusion is that the changes in the Atlantic are the cause of the changes in Ireland’s temperature, though this is not concrete proof.
Additionally, the AMO appears to effect summer rainfall in Northwestern Europe. Negative, cooler cycles of the AMO are associated with drier seasons, positive, warmer cycles with wetter weather. The records only go back to the early 1940s, so there is not enough data yet to prove a link, but the correlation is notable.
So there you have it; the Atlantic’s likely influences on Ireland’s temperature. There may well be other factors involved, but the focus today was on the AMO. Areas of scientific interest are rarely simple or involve only one factor. It is part of what makes them interesting, Ireland being no exception.

 

Bibliography
NASA Earth Observatory. “Ireland : Image of the Day.” 11 Oct. 2011. Web.
The source for the image used in today’s post.
McCarthy, G. D., Gleeson, E. and Walsh, S. (2015), The influence of ocean variations on the climate of Ireland. Weather, 70: 242–245. doi: 10.1002/wea.2543
Today’s featured article.

 

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