As spatial and temporal scales decrease, attribution of climate change becomes more difficult. (scientificamerican.com)
In fact, scientists have long recognized the importance of solar variability as one of the factors governing climate (see the very scholarly review of the subject by Bard and Frank, available here at EPSL or here as pdf) An understanding of solar variability needs to be (and is) taken into account in attribution of climate change of the past century, and in attempts to estimate climate sensitivity from recent climate variations. (realclimate.org)
An important question in current climate change research is over attribution of climate change to either natural / internal or human factors over the period of the instrumental record — from about 1860, and especially over the last 50 years. (sciencedaily.com)