1) 20th century over Northern Europe. There has been little trend in winters over this region during the 20th century because winters were mild in the first 40 years of the century.
2) Central and Eastern Siberia. Data is sparse for these regions earlier this century. What Bill has said here is defensible, but it would seem best to remove this sentence, because it is very difficult to be certain either way. The trends in N. China relate to the period since 1951. Since 1951 winters in C and E Siberia have warmed, but they were milder in the first part of the century as in parts of Europe.