Climate change, defined by the Environmental Protection Agency as any significant change in climate measures lasting for an extended period, is fundamentally altering ecosystems worldwide while prompting unprecedented policy responses from governments and international organizations.

Marine environments face particularly severe impacts as ocean acidification makes it increasingly difficult for calcifying organisms such as mussels, barnacles, and corals to produce shells and skeletons. Coral reefs have experienced widespread bleaching due to marine heatwaves, while harmful algal blooms enhanced by climate change and nutrient pollution are lowering oxygen levels and disrupting food webs, causing significant losses of marine life.

International Response and Policy Development

The global response has included major international conferences, with some climate summits hosting more than 10,000 delegates and marking significant milestones such as the entry into force of the Kyoto Protocol. These gatherings represent some of the largest intergovernmental conferences on climate change in history, reflecting the scale of international cooperation required to address the challenge.

The World Health Organization has identified climate change as a critical public health challenge, highlighting the connection between environmental changes and human health outcomes. Meanwhile, the feasibility of replacing fossil fuels with renewable energy sources has significantly increased since the 2020s, with some countries now generating almost all their electricity from renewable sources.

Scientific Understanding and Public Awareness

Public awareness of climate threats has risen substantially, driven in part by youth-led social movements and increased visibility of climate impacts including extreme weather events and flooding caused by sea level rise. However, scientific understanding continues to evolve, with researchers examining various factors that contribute to observed changes.

Historical perspective shows that atmospheric changes have shaped life on Earth before, such as when cyanobacteria released molecular oxygen as a photosynthesis byproduct, creating novel evolutionary challenges that ultimately led to the formation of Earth's major animal and plant species. This precedent demonstrates how atmospheric composition changes can fundamentally reshape planetary ecosystems over time.