Exceptional Warmth

It’s been a while since I last posted an interesting chart. Here’s another one. I first came across it in a lecture I attended titled “Ocean Circulation and Climate” given by Helen Johnson last year. The chart was produced by Stefan Rahmstorf, a version is included in the following paper, available on his website:

Rahmstorf, S. and A. Ganopolski, 1999: Long-term global warming scenarios computed with an efficient coupled climate model. Climatic Change, 43, 353-367.

Deviation of the annual mean surface air temperature from its zonal average - Rahmstorf (1999)

The provided caption reads:

Deviation of the annual-mean surface air temperature from its zonal average, computed from the NCAR air temperature climatology. Anomalously cold areas are found over some continental regions, anomalously warm areas over ocean deep water formation regions.

The term “zonal average” means the average along a line of latitude. Meridional refers to longitude (think Greenwich Meridian). The chart shows that the average air temperature off Scandinavia is some 10 °C warmer than the average temperature at the latitude (60 to 70 degrees North). NCAR refers to The National Center for Atmospheric Research.

Rahmstorf explains in his paper how this temperature deviation is the result of heat being transported by ocean currents, currents that do vary over time and could be impacted by future climate change. This warming is the result of the thermohaline circulation (THC), driven by global density gradients created by surface heat (thermo) and freshwater fluxes (haline). Variation in the THC could have a dramatic cooling influence in the North Atlantic as climate change impacts both heat and freshwater flux. As far as I am aware though it is not currently possible to measure and model the interactions accurately enough to make confident predictions about the likelihood of the THC being significantly impacted as a result of climate change.

I think this is an interesting chart as it illustrates just how exceptionally warm the North Atlantic and northwestern Europe are for their latitude. The UK for example sits between 50 and 60 degrees North. Within that band we also find the southern tip of Greenland, Vancouver (home of the 2010 winter Olympics), Moscow and the chilly waters of Hudson Bay and the Gulf of Alaska.