Climatic changes are taking place that the scientific community does not fully understand. Researchers at the Nansen Center have investigated the impact that changes in an atmospheric phenomenon over the North Atlantic can have on our winter weather.
Many studies have been carried out to analyse the development of winter weather. Different factors can affect winter weather in Europe;
- Anthropogenic climate change affects temperature, precipitation, and winds.
- The Gulf Stream carries warm water northwards and affects the climate.
- Air currents high in the atmosphere control the flow of cold air from the Arctic and warm air from the south.
- The North Atlantic Oscillation (NAO) affects the direction and strength of winds over the North Atlantic.
The Nansen Center has conducted research into how much of the variation in the weather can be explained by the influence of the North Atlantic Oscillation (NAO), and how this has developed from 1930 until the end of the last century.
The NAO is a measure of the difference in air pressure over the North Atlantic, from the Azores in the south to Iceland in the north. The size of the difference in air pressure determines how much wind from the west hits Europe and whether the wind goes far south or far north. This in turn determines whether the winter weather will be wet and mild in southern Europe and dry and cold in the Nordic countries, or vice versa.
Climate researchers Stephen Outten and Richard Davy have taken a closer look at the NAO and the changes in this phenomenon over the past 100 years. In their work, they have used climate models that simulate weather and climate conditions using mathematical formulas. Such models are useful both for predicting future climate and for understanding past weather patterns. The researchers have compared results from the climate models with a historical reanalysis. A reanalysis provides a detailed overview of past weather and climate conditions by combining historical data with a modern weather forecasting model. By comparing the results from the climate models with the reanalysis, it is possible to understand the development of climate conditions and assess how well the climate models actually work.
Outten and Davy discovered that the weather in Europe around 100 years ago was less influenced by the NAO than it is today. Towards the end of the 20th century, the influence of the NAO accounted for about half of the variations in the mean sea level pressure over the North Atlantic, while 100 years ago the NAO only accounted for a third. This means that the NAO has become an increasingly important factor in the development of winter weather, while other influencing factors have become less important. The researchers have not found a clear answer to whether this change is due to natural processes, climate change, or a combination of these. However, Outten and Davy demonstrate that the climate models show no evidence that this change is due to climate change, suggesting that the increased importance of the NAO is due to natural variability.
The research results also show that most of the climate models used in the work did not simulate the changes in the NAO that have actually taken place. The research shows that there is a need for further improvements to the climate models.
Key researchers: Stephen Outten, Richard Davy
