ABSTRACT
This chapter describes key components of the carbon cycle and shows how the global carbon cycle has been recently modified by human action, with very rapid changes in the most recent decades. The chapter covers Quaternary climate change, describing the glacial and interglacial cycles over the past 2.4 million years. The driver of Quaternary change was orbital forcing, but additional feedback processes on Earth were essential to reinforce or dampen climate change experienced; of particular importance were ocean circulation systems. The chapter also deals with contemporary climate change and evidence compiled by the Intergovernmental Panel on Climate Change. The concentrations of greenhouse gases in the atmosphere are greater than at any time in at least the last 800 000 years and their concentrations have risen sharply in recent decades. Evidence for human influence on recent warming of the climate system is compelling, and since the 1950s many of the observed changes are unprecedented over millennia. The impacts of contemporary climate change will be far reaching, costly and hazardous. The chapter covers climate change mitigation strategies and the ‘net zero’ activities resulting from the 2015 Paris Agreement, including the use of low carbon energy sources and facilitation of enhanced carbon capture. Adaptation measures need further investment and development to deal with future impacts of climate change that will happen as result of anthropogenic emissions that have already occurred.
