Natural random fluctuations in our climate are not sufficient to explain recent rates of global warming, a study shows.
University scientists used both models and climate records from the early middle ages to the present day for their study.
Evidence from tree rings, ice cores, corals and sediments was used, together with complex computer models, to separate the impact of factors such as volcanic activity, variations in the sun’s output, and greenhouse gases from the records.
Their results, once accounting for these factors, showed substantially less variation compared with 20th century climate records.
Estimates of natural change are usually derived from climate models, so this study provides an important test of scientists’ understanding of natural variability
The study shows for the first time that carbon dioxide contributed to the cold conditions during the little ice age, which led to widespread cooling in Europe, approximately from the 1500s to the 1800s.
The paper is published by the Journal of Climate.
The study was carried out in collaboration with researchers from Pennsylvania State University and the University of New South Wales.