Climate Change: Science, Evidence and Projections

Climate change is the defining environmental challenge of the twenty-first century. The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report concludes that human influence has unequivocally warmed the atmosphere, ocean and land, with widespread and rapid changes across the climate system (IPCC, 2021, 2023). This chapter examines climate change science from the molecular physics of the greenhouse effect and carbon-cycle chemistry through attribution evidence, feedbacks, scenario construction, projected physical and ecological impacts, carbon budgets and climate tipping points. The emphasis is on how multiple independent observational and modelling approaches converge on the same central conclusion: continued greenhouse-gas emissions cause continued warming and progressively greater risks to ecosystems and human societies.