One of the main points that I have been making on this website and in my book is that the Earth was much warmer 6,000 years ago than it is today. In the book I point out many examples of glaciers that have only formed in the past few thousand years. I am always looking at new data as it becomes available and recently there was a nice study in Quaternary Research that did a study on glacial activity in Norway for the past ~8,000 years. This is the kind of study I love to find because it covers a long period of time that includes the current period. It is surprising how few studies cover a range like this.
The study went after a variety of sediments in the lake bed to determine the sediment that was depositing in the lake. By determining the different compositions in the sediment they could find how much glacial activity was taking place over the past 8,000 years. This would make sense because rainfall over ground draining into a river would pick up different minerals than the melt from a glacier.
Here is the official chart from the study itself.
The highlighted areas are periods where the sediment is dominated by non-glacial markers. Most of the period from 8,000 – 4,000 years ago is dominated by periods with little to no glacial activity. Certainly this is solid evidence that the current climate of Norway is not abnormally warm as some would have us believe. What is clear is that the glacial activity has been the highest for the past 1,000 years.
Astute readers will notice the brief periods from 1,000 and 2,000 years ago that are commonly referred to as the Medieval and Roman Warming periods. Both are simply interludes of the expanding glacial activity that has steadily been taking place for the past 4,000 years. Those periods are important to the study of glaciers for other reasons that I would also like to discuss.
Ice cores from glaciers are useful only when they have an uninterrupted layers of ice. Warm periods or glaciers that flow cannot provide a useful ice cores, which is why ice cores come from such a limited set of sources. Glaciers that have formed in the region of this study over the past 4,000 years would have experienced several periods where they were shrinking if not completely eliminated. This type of sediment study will greatly increase the number of glaciers that can be usefully studied.
This study is not an anomaly either. Any study of the Northern Hemisphere shows this exact overall behavior. The NH was warmer several thousand years ago, even though the CO2 level was lower. There has been a general cooling trend throughout the NH over the past 4,000 years. It is not steady by any means over a period of a few hundred years, but over the course of thousands of years it is very steady. This is simply one more study that shows the same thing.
The authors of the study simply state their findings in their abstract.
ABSTRACT: We explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large (440 km2) glacierized catchment in western Norway, as recorded in the downstream lake Nerfloen (N61°56', E6°52'). A multi-proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the ~8000-yr-long record, based on distinct changes in grain size, geochemistry, and magnetic composition. Principal Component Analysis (PCA) reveals a strong common signal in the 15 investigated sedimentary parameters, with the first principal component explaining 77% of the total variability. This signal is interpreted to reflect glacier activity in the upstream catchment, an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples. Minimum glacier input is indicated between 6700-5700 cal yr BP, probably reflecting a situation when most glaciers in the catchment had melted away, whereas the highest glacier activity is observed around 600 and 200 cal yr BP. During the local Neoglacial interval (~4200 cal yr BP until present), five individual periods of significantly reduced glacier extent are identified at ~3400, 3000-2700, 2100-2000, 1700-1500, and ~900 cal yr BP.
The authors simply state that most glaciers likely didn’t exist 6,000 years ago, but the highest period of the glacial activity has been in the past 600 years. Seems pretty straightforward to me.