Heinrich events, in which large masses of icebergs rapidly broke free from ice sheets during the last ice age, are thought to have influenced global climate by interrupting ocean circulation patterns with a large influx of freshwater. However, new research from the University of Bristol suggests the variations in the height of the ice sheet that happen in these events might also influence global climate. In a study published today in PNAS, Dr William Roberts of Bristol’s School of Geographical Sciences and colleagues use computer models to simulate a Heinrich event in Hudson Bay, Canada, adjusting the models to consider freshwater influx only, changing ice sheet height only or both factors together.