Updating our understanding of climate change in the North Atlantic: the role of global warming and the Gulf Stream

ABSTRACT

It is well accepted that the temperate nature of UK/Europe climate is heavily dependent on the Gulf Stream. Many modelled studies have shown that ocean freshening in the North Atlantic by global warming will reduce the strength of the Gulf Stream – an ocean current thought to be principally driven by ocean density (i.e. temperature and saltiness) differences in the high North Atlantic (O'Hare et al., 2005). If weakening in the Gulf Stream occurs gradually over the 21st century (IPCC, 2007), a possible amelioration of the rising temperatures brought about by global warming could occur over the UK and Western Europe. However, if the Gulf Stream collapses in just a few decades, there could be an abrupt onset of very cold conditions over the region (Jenkins, 2007). In recent years a major paradigm shift has occurred in our understanding of the processes that transport not only the Gulf Stream but also ocean currents in general. It is becoming clear that winds in the atmosphere drive most of the circulation in the ocean. Indeed, references to the idea that density differences in the ocean, caused by thermohaline variations in temperature and saltiness, have diminished in recent oceanographic literature (Toggweiller and Russell, 2008). These new ideas concerning winds and on how currents are transferred in the oceans have reduced the theoretical threat of Gulf Stream collapse and respective cooling over the North Atlantic region. They have also unfortunately diminished the possibility of a scaling down of the future impact from global warming over the region.