The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 11,700 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.
The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20th century and proceeding at a rate that is unprecedented over decades to millennia.1
Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about the planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.
1 IPCC Fifth Assessment Report, Summary for Policymakers