Climate change refers to long term shifts in temperature, precipitation and other aspects of Earth’s climate system driven largely by human activities. The central driver is the enhanced greenhouse effect. Rising concentrations of carbon dioxide, methane and nitrous oxide trap more heat in the atmosphere. These gases come mainly from burning fossil fuels, deforestation, agriculture and industrial processes. Measurements from ice cores and modern instruments show that current greenhouse gas levels are far higher than at any time in at least 800 000 years.

Global average surface temperature has already risen by more than 1 degree Celsius since the late nineteenth century. Warming is not uniform. The Arctic is heating much faster than the global average, triggering sea ice loss, permafrost thaw and feedbacks that can release additional greenhouse gases. Oceans absorb most of the excess heat, leading to thermal expansion of seawater and sea level rise, as well as more frequent marine heatwaves and coral bleaching.

Climate change alters the hydrological cycle. Many regions experience more intense rainfall events and flooding, while others face longer and deeper droughts. Heatwaves are becoming more frequent, more intense and longer lasting, raising health risks and straining energy systems. Shifts in climate zones affect ecosystems, species distributions and agriculture, with some crops already showing yield reductions in vulnerable regions.

Future climate outcomes depend strongly on emissions pathways. Rapid cuts in greenhouse gas emissions, protection and restoration of ecosystems, and changes in energy, transport and food systems can limit further warming and reduce the risk of crossing critical climate tipping points.