The Day After Tomorrow
A new Hollywood disaster movie, 'The Day After Tomorrow,' is released worldwide on 28 May 2004. It shows what type of very extreme weather events could happen if the Gulf Stream in the North Atlantic Ocean suddenly 'switched off' within a few days as the result of global climate change. The Gulf Stream currently creates a warm climate in north western Europe (warmer than at equivalent latitudes). The film shows the effects of, for example, huge tidal waves, hail storms, and an abrupt and dramatic cooling ("new Ice Age") in the northern hemisphere.
The general scientific view is that the timescales shown in the movie and some of the extreme climatic events are very unrealistic and much of the science behind the film cannot be supported. However some of the science is real. There is scientific agreement that the probability of a Gulf Stream switch-off and a substantial cooling in the Northern Hemisphere in the next hundred years and beyond are extremely low, since the ongoing global warming would offset any regional cooling. In the very unlikely scenario that the Gulf Stream would switch off, there would be cooling in North West Europe with associated impacts on agriculture and water resources, but this would not be a global phenomenon. However, ongoing and projected gradual global climate change does pose a large threat to human society and the environment, and the film helps to increase awareness of this problem.
Source: Twentieth Century Fox, 2004
Of the following information, presented here, the UK Met Office Hadley Centre for Climate Prediction and Research has provided the sections on "How the Gulf Stream works" and "What might happen in future".
How the Gulf Stream works
Figure 1 - Global ocean circulation
Source: Hadley Centre
North western European countries are much warmer than other countries on the same latitude, and this is partly due to the Gulf Stream - a current of warm water that flows from the Gulf of Mexico past the shores of western north western Europe. It is part of a larger system of ocean currents (with a hundred times the flow of the Amazon) often called the 'conveyor belt' (or officially "Thermo-haline circulation"). The engine that drives this conveyor is in the northern Atlantic and the Arctic; the relatively warm, salty, northward flowing surface sea water there is cooled by bitter winds, becomes denser, sinks to the bottom of the ocean and flows south. If it did, a 'what-if' experiment with the Hadley Centre climate model shows that the UK (and similarly other NW European countries) would cool by up to 5 °C, and it could happen in a matter of a decade or two. If it did happen, the disruption to society would be enormous.
What might happen in future?
The Gulf Stream has switched off before, at the end of the last ice age about 13,000 years ago, when meltwater from a huge glacier in Canada flowed into the North Atlantic and stopped the sinking mechanism. Europe cooled by several degrees in only one or two decades. It has however been relatively stable for about the past 8000 years. The Hadley Centre using their climate model analysed the effect on the Gulf Stream of future climate change, caused by the greenhouse effect as carbon dioxide is emitted in ever-increasing quantities. Additional heat and freshwater in the North Atlantic and Arctic, due to global warming and coming from increased rainfall, melting of Greenland ice and increased river discharge in the Arctic basin, could disrupt the sinking of the warm salty water and thereby halt the thermo-haline circulation.
The current scientific consensus (as expressed by the UN Intergovernmental Panel on Climate change, IPCC, see: http://www.ipcc.ch/) is that global warming, on the timescale of the next 50-100 years, may result in a weakening of the Gulf Stream, by about 20% by the middle of the century, but is unlikely to shut it down completely. The predictions of the best models (including that of the UK's Hadley Centre) are that north-west Europe will still warm but perhaps less so than if the Gulf Stream had not slowed.
However, although the probability that global warming could lead to complete halt of the Gulf Stream appears to be very small, it cannot be completely ruled out. This is therefore an area of active research. The Hadley Centre and the Natural Environment Research Council, with researchers from Norway and the Netherlands, are addressing the issues in a major research programme. This aims to improve our understanding and reduce the remaining substantial uncertainties on processes in the earth's complex climate system and the oceans that could affect the Gulf Stream.
Need for adaptation and mitigation of climate change
Global and European climate has changed in the recent past. Temperatures are rising, frequencies of extreme weather events are increasing and precipitation in many parts of Europe is changing. Over the past 100 years global mean temperature has increased by 0.6 °C and in Europe by about 1.0 °C and the 1990s was the warmest decade over the past 150 years. Temperatures are projected to increase further by 1.4 to 5.8°C by 2100, with larger increases in Eastern and Southern Europe. According to the IPCC "there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities", in particular to the emissions of greenhouse gases, see the IPCC Third Assessment Report - Climate Change 2001 (IPCC, 2001), see http://www.ipcc.ch/.
The magnitude of the impacts in future strongly depends on the nature and rate of future temperature increase. Consequences of climate change include an increased risk of floods and droughts, losses of biodiversity, threats to human health, and damage to, but in some cases also new possibilities for, economic sectors such as forestry, agriculture, tourism and the insurance industry (IPCC, 2001). Some of these impacts are already beginning to appear.
Within Europe, as well as within many other countries that have ratified the UN Framework Convention on Climate Change (UNFCCC), there is a growing recognition that increased efforts on adaptation measures are required, while at the same time continuing to develop and implement policies and measures to reduce greenhouse gas emissions.
The EEA is preparing an indicator-based assessment of recent and projected climate changes and their impacts in Europe for publication in the coming months. The report aims to assess the vulnerability of ecosystems, human health and socio-economic sectors, to climate change and enable the development of adaptation strategies, but also to enhance the sense of urgency to implement mitigation measures.
The North Atlantic and Arctic oscillations
Climate variation is often associated with oscillations, cyclical shifts in the weather and ocean currents. For Europe the most important are the North Atlantic oscillation, which primarily affects weather patterns in Europe and the Arctic oscillation, which has its main impact in the Arctic. These oscillations are strongly interlinked. During the 1990s, the Arctic oscillation was extremely high, and the weather associated with low-pressure systems penetrated further north, resulting in higher than normal rainfall and temperatures across western Europe and Scandinavia. The reason for the extreme high Arctic oscillation conditions in the 1990s is unclear. It could have been a response to global climate change, or a result of natural variability, or a combination of both. Whatever the reason, the 1990s might be an example of what can be expected as the more normal situation in the future (EEA report "Arctic Environment: European perspectives", forthcoming).
Climate Research Unit, The thermohaline circulation.
Hadley Centre (2004), Global warming - will we freeze? What the experts are really saying.
Gagosian, Robert B. (2003), Abrupt Climate Change: Should We Be Worried? Woods Hole Oceanographic Institution. Prepared for a panel on abrupt climate change at the World Economic Forum Davos, Switzerland. January 27, 2003
German Environment Ministry, Konsequente Klimaschutzpolitik kann Klimakatastrophen verhindern
Hulme, Mike (2003), Abrupt Climate Change: Can Society Cope? Tyndall Centre for Climate Change Research, Working Paper 30. March 2003.
IPCC (2001), Third Assessment Report - Climate Change 2001
EEA (2003), Europe's environment: the third assessment, Environmental assessment report No 10, chapter on climate change
EEA (2004), Mapping the impacts of recent natural disasters and technological accidents in Europe, Environmental issue report No 35. http://reports.eea.eu.int/environmental_issue_report_2004_35/en
EEA (2004), Arctic Environment: European perspectives
Official website of the movie The Day After Tomorrow"