Global warming refers to the increase in average temperatures around the world due to rising levels of greenhouse gases like carbon dioxide in the atmosphere. Greenhouse gases occur naturally but human activities like burning fossil fuels have increased their levels, trapping more heat from the sun and changing the climate. Effects of global warming include melting ice caps, rising sea levels, more extreme weather, and threats to human health and agriculture. Individual actions like using less energy, driving less, recycling, and planting trees can help address the problem.