The purpose of this excerpt from a speech is to convey the urgency and significance of global warming as a collective concern. It aims to broaden the audience's awareness, emphasizing that everyone, not just experts or environmentalists, should be mindful of the issue. The speaker seeks to highlight the human responsibility for causing global warming and stresses the potential severe consequences, such as rising sea levels, melting glaciers, altered weather patterns, and impacts on ecosystems, ultimately emphasizing the need for collective action to address and mitigate these challenges.