Climate Change During the Holocene (Past 12,000 Years)

Abstract

This chapter summarises the climatic and environmental information that can be inferred from proxy archives over the past 12,000 years. The proxy archives from continental and lake sediments include pollen, insect remnants and isotopic data. Over the Holocene, the Baltic Sea area underwent major changes due to two interrelated factors-melting of the Fennoscandian ice sheet (causing interplay between global sea-level rise due to the meltwater and regional isostatic rebound of the earth's crust causing a drop in relative sea level) and changes in the orbital configuration of the Earth (triggering the glacial to interglacial transition and affecting incoming solar radiation and so controlling the regional energy balance). The Holocene climate history showed three stages of natural climate oscillations in the Baltic Sea region: short-term cold episodes related to deglaciation during a stable positive temperature trend (11,000-8000 cal year BP); a warm and stable climate with air temperature 1.0-3.5 °C above modern levels (8000-4500 cal year BP), a decreasing temperature trend; and increased climatic instability (last 5000-4500 years). The climatic variation during the Lateglacial and Holocene is reflected in the changing lake levels and vegetation, and in the formation of a complex hydrographical network that set the stage for the Medieval Warm Period and the Little Ice Age of the past millennium. 2.1 Introduction The evolution of the coastline in the Baltic Sea area since the end of the last deglaciation has been the object of study for more than one hundred years. Despite this, some questions remain concerning both the chronologies of the transgression regression phases of the prehistoric Baltic Sea basins and their spatial characteristics. Nevertheless, the long-term change in environmental conditions does provide information about the magnitude of natural climate and environmental variability, both that resulting from external climate drivers and that internally generated. This knowledge is important not only for understanding the mechanisms driving variability and the trend in climate change over centennial timescales,