Birds is Asia, North America and South America suffered much less change in their levels of infection during warm years than did birds dwelling in Africa and Europe.
In warm years, trees tend to produce wider, denser rings and in cool years, the rings are typically narrower and less dense.
In early summer they migrate to the northern end of the Tatar Strait and, in warm years, even to the eastern shore of the Kamchatka Peninsula.
England is set to experience a significant increase in the number of record-breaking warm years due to the influence of greenhouse gas emissions, scientists said.
As the sequence approaches the present, the cello reaches higher and higher notes, reflecting the string of warm years in the 1990s and 2000s.
Climate scientists have been reluctant to link the long-term warming trend to individual natural disasters or even single warm years.
The previous year was the warmest on record, coming on top of a run of record warm years in the warmest decade of the century.
El Niño has exerted a powerful influence in many other recent unusually warm years, including 1998, the warmest year on record.
As NASA GISS director Gavin Schmidt said, This is the latest in a series of warm years, in a series of warm decades.
He says a succession of warm years in Alaska has allowed spruce bark beetles to reproduce at twice their normal rate.
As for record warm years, these will likely coincide with El Niño conditions, which occur as part of a natural cycle in the Pacific Ocean.
