Even with a long - term background trend of rising temperatures, other climate factors contribute to yearly ups and downs. (scientificamerican.com)
To me, the more subtle background trend is the significant one to watch because it's like the long - term warming of the climate itself. (dotearth.blogs.nytimes.com)
On the basis of the above two charts it seems that the global background trend in stratosphere and troposphere is not significantly affected by volcanic events or individual El Nino events. (newclimatemodel.com)