The major cause of global warming is the burning of fossil fuels. Fossil fuels like coal, oil, and natural gas are burnt to produce energy for electricity, transportation, and other human activities. This process releases large amounts of greenhouse gases, particularly carbon dioxide, into the atmosphere. These gases trap heat from the sun, causing the Earth's temperature to rise, resulting in global warming. The other options mentioned, such as construction of dams, use of electricity, and exploration of space, do not have as significant an impact on global warming as burning of fossil fuels.