Carbon dioxide from human activity is increasing more than 250 times faster than it did from natural sources after the last Ice Age. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that Earth’s climate responds to changes in greenhouse gas levels. There is no question that increased levels of greenhouse gases must cause Earth to warm in response. 2 Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. This body of data, collected over many years, reveals the signals of a changing climate. 1 It is undeniable that human activities have warmed the atmosphere, ocean, and land and that widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.Įarth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. The current warming trend is of particular significance because it is unequivocally the result of human activity since the mid-20 th century and proceeding at a rate that is unprecedented over millennia.
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