Discussion and conclusion

Presented results proved that the Atlantic-Arctic climate system components are closely interrelated. Moreover, fluctuations in the Atlantic SST modulated corresponding oscillations in many other subsystems: Eastern Arctic ice extent, land surface pressure, SST in shelf seas, surface air temperatures in North Asia.

The key to the new climate change outlook is the natural cycle of ocean temperatures called the Atlantic Multidecadal Oscillation (AMO), which is closely related to the warm currents that bring heat from the tropics to the shores of Europe. The cause of the oscillation is not well understood, but our study proved that the cycle appears to come round about every 60-70 years. It may partly explain why temperatures rose in the early years of the last century before beginning to cool in the 1940s. One message from our study is that in the short term, you can see changes in the global mean temperature that you might not expect given the reports of the Intergovernmental Panel on Climate Change (IPCC). But in the long term, radiative forcing (the Earth's energy balance) dominates.

Modeling of climatic events in the oceans is difficult, simply because there is relatively little data on some of the key processes, such as the meridional overturning circulation (MOC) - sometimes erroneously known as the Gulf Stream -which carries heat northwards in the Atlantic. Only within the last few years have researchers begun systematically deploying mobile floats and tethered buoys that will, in time, tell us how this circulation is changing. Looking forward, our results can suggest a weakening of the MOC and a resulting cooling of north Atlantic waters, which will act to keep temperatures in check around the world, much as the warming and cooling associated with El Nino and La Nina in the Pacific bring global consequences.

Recent observing data have led to a conclusion that a slowly fluctuating oscillation in Pacific Ocean temperatures had shifted into its cool phase, a condition that is also thought to exert an overall temporary cooling of the climate. Of course, these natural variations can also amplify warming, and that is likely to happen in future decades on and off as well. The global climate will continue to be influenced in any particular decade by a mix of natural variability and the building greenhouse effect.

This projection does not come as a surprise to climate scientists, though it may to a public that has perhaps become used to the idea that the rapid temperature rises seen through the 1990s are a permanent phenomenon. We have always known that the climate varies naturally from year to year and decade to decade. We can expect man-made global warming to be superimposed on those natural variations; and this kind of research is important to make sure we don't get distracted from the longer term changes that will happen in the climate (as a result of greenhouse gas emissions). It should also help the public and policy makers understand that a cool phase does not mean the overall theory of human-driven warming is flawed.

No doubt we need to have more data from the deep ocean, and we don't have that at present. But imagine the payoff of knowing with some certainty what the next 10 years hold in terms of temperature and precipitation - the economic impacts of that would be significant.

Acknowledgements

NATO ARW provides a financial support for the conference participation and publication of this proceedings volume.

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