The reason that the first half of this winter was warm was that the May 2011 eruption of Mt. Grimsvötn in Iceland changed the atmospheric pressure in the North Atlantic. This altered the oscillations in the Arctic and North Atlantic so much that they overruled almost all cooling from the La Niña.

The Arctic Oscillation became positive, pinning the cold Arctic air in the north for the first half of winter. It has turned negative and is letting freezing weather hit Europe, damaging winter wheat crops.

The North Atlantic Oscillation became positive, helping to pin the Arctic air in the north. It is now rotating between positive and neutral, allowing occasional cold in North America for brief spells.

Without the Icelandic effect, the La Niña has had its full impact in the Southern Hemisphere. Larger cycles in the Pacific have strengthened the weather impact of the moderate La Niña.

The La Niña has created drought and crop problems in South America, heat and floods in Australia and decent growing conditions in large areas of Southern Africa.

David Fuller's view I think many subscribers will find this issue particularly interesting.

For pre-subscriber visitors to this site who would like to see a back issue of the Browning Newsletter on Climate, use the 'Search' facility shown in the menu upper left, fourth item down and search under Browning.