Could it really happen?

According to Al Gore, former Vice President of the USA, this is likely to be the question on millions of people's lips after seeing 20th Century Fox's new disaster film 'The Day After Tomorrow', and one that deserves an answer.

Fortunately, rapid climate change is one area that the UK has taken the lead in researching, by funding the Rapid Climate Change programme (RAPID), the aim of which is to determine the probability of rapid climate change occurring.

The film
The Day After Tomorrow focuses on the research of climatologist Jack Hall, which indicates that global warming could trigger a rapid change in the global climate as a result of the Gulf Stream shutting down. Reports soon come in that this is already happening and a dramatic sequence of extreme weather events follow, which include a new Ice Age engulfing most of the Northern Hemisphere.

The facts
The Gulf Stream is a branch of the global thermohaline circulation (THC), driven by differences in temperature and salinity of sea water, that brings warm water north from the Caribbean to the UK and north west Europe.

The experts
The Gulf Stream is a branch of the global thermohaline circulation (THC), driven by differences in temperature and salinity of sea water, that brings warm water north from the Caribbean to the UK and north west Europe.

Dr Geoff Jenkins, senior climate researcher at the Hadley Centre, said that the film does have a basis in theory. "If the Gulf Stream did shut down, the UK and northwest Europe would become colder, but over a much longer timescale - the film makers have crammed what would happen in a decade into a few hours".

3-4°C may not sound much, but the average air temperature difference between the 'Medieval Warm Period' when vineyards thrived in southern England and the 'Little Ice Age' when the River Thames regularly froze over was only 1-2°C.

Some good news though, Dr Jenkins doesn't believe that the extreme follow-on of events such as snow in New Delhi, tornadoes destroying Los Angeles and grapefruit size hail in Tokyo are likely to happen.

Dr Meric Srokosz is Science Coordinator of RAPID. "Greenland ice cores and North Atlantic marine sediments show that rapid climate changes have occurred repeatedly in the past. Changes as large as 5-10°C over periods as short as a decade; fast for Climate Change where we usually think in terms of centuries or millennia. These data also show that the ocean circulation is implicated in many of these rapid changes."

He said of the film "It telescopes events, such as the shutdown of the North Atlantic circulation, into a few days (it would take years to happen in reality) and amplifies the impact of the events (we are not headed for another Ice Age). The ocean circulation might slow down in the future and this might lead to somewhat cooler temperatures (by a few degrees) in the UK and NW Europe, but not to the disaster depicted in the film."

The future

Dr Srokosz said "Present day observations suggest that changes are occurring in the North Atlantic circulation... however existing observations are not adequate to answer the question of whether the THC is slowing down."

"Rapid climate change is a low probability but high impact event, so we need to improve our knowledge of the processes involved and narrow the uncertainties on the prediction of potential future rapid climate change." Which is what RAPID aims to do.