Climate is the average of weather conditions over decades to centuries in a particular location. Climate is influenced by many factors, including solar activity, ocean circulation, land cover, and greenhouse gases and aerosols in the atmosphere.[2,3,4,5]
Records from Earth's geologic history show that the climate has changed both gradually and abruptly in the past, and that global temperatures and the concentrations of greenhouse gases in the atmosphere are strongly correlated. Many of the concerns over human influences on climate are due to the significant emissions of greenhouse gases from human activities since the mid-19th century[2,7]. Natural processes will always have strong effects on climate, but there is evidence that these greenhouse gas emissions, combined with other human activities such as aerosol emissions and land-use changes, are linked to the rapid warming that has been observed since the middle of the 20th century[2,3,4,7,8,9,10,11,12]. Since the start of the 20th century, average global temperatures have increased, with most of the warming occurring since the 1970s[7,8,9]. All 10 of the warmest years since records began have occurred since the early 2000s, and average global temperatures are expected to increase at least 2 ºF, and perhaps by as much as 11 ºF, over the next century[10,11].
How does geoscience inform decisions about climate?
The Earth system is a complex one, and it is not always easy to predict the precise effects of geological processes or human activities, particularly on geologically short timescales of years to decades. Geoscientists use historical measurements, data from the geologic record, and real-time data to constantly improve their understanding of the Earth system and to predict future climate changes due to both natural causes and human activities.
32014 National Climate Assessment: Land Use and Land Cover Change U.S. Global Change Research Program
4FAQ: How do changes in climate and land use relate to one another? U.S. Geological Survey
6Temperature change and carbon dioxide change National Oceanic and Atmospheric Administration
72014 National Climate Assessment: Future Climate Change U.S. Global Change Research Program
8Climate Change Facts: Evidence National Oceanic and Atmospheric Administration
9FAQ: Is the globe still warming today? National Oceanic and Atmospheric Administration
10Global Climate Change Indicators National Oceanic and Atmospheric Administration
11Advancing the Science of Climate Change The National Academies
122014 National Climate Assessment: Recent U.S. Temperature Trends U.S. Global Change Research Program