Below we've compiled some of the most relevant statistics on climate change from credible peer reviewed and nonpartisan scientific sources. We also feature answers to common questions from students about climate change over in our Information Station.

Findings from the IPCC AR4

In 2007, the Intergovernmental Panel on Climate Change (IPCC) released its Fourth Assessment Report (AR4). The report is the work of the world’s leading climate scientists and includes the input of more than 1,200 authors and 2,500 scientific expert reviewers from more than 190 countries. ACE relies on the IPCC AR4 to provide accurate and current climate science to students. Some of the key findings include:

1. The warming of the climate is beyond doubt. The report finds that “the warming of the climate system is unequivocal … as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level.”
2. Humans are almost certain to be responsible for this warming. The report states that “most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to [human activity].” The IPCC defines “very likely” as greater than 90% certainty.
3. Storms are more intense. The intensity of hurricanes in the North Atlantic has increased over the past 30 years.
4. Flooding and drought are more severe. Storms with heavy precipitation have increased in frequency over most land areas, leading to more flooding. Droughts have become longer and more intense, and have affected larger areas since the 1970s, especially in the tropics and subtropics.
5. Glaciers are melting. Mountain glaciers and snow cover have declined worldwide.
6. Species face extinction. Up to 30 percent of plant and animal species could face extinction if the global average temperature rises more than 3 to 5°F.
7. Temperatures are rising. Global average temperatures have already risen 1.44 degrees Fahrenheit. The IPCC’s best estimate range of projected temperature increase is 3.1 to 7.2 degrees Fahrenheit.
8. Water resources are threatened. Hundreds of millions of people face water shortages that will worsen as temperatures rise. Most at risk are current drought-affected regions, areas with heavily used water resources, and areas that get their water from glaciers and snowpack.

                                                 
 Arctic Sea Ice Extent in Summer of 1980 and in Summer of 2007.  Source: NASA

Major findings since the IPCC AR4

1. CO2 levels continue to climb. As of June, 2009, the concentration of CO2 in the atmosphere is 389ppm, which is higher than it has been on Earth for at least the past 2.1 million years. (Source: Honisch B, Hemming NG, Archer D, Siddall M, McManus JF. 2009. Atmospheric Carbon Dioxide Concentrations Across the Mid-Pleistocene Transition. Science. 324 (5934): 1551-1554.)
2. The globe is experiencing the hottest years on record. According to the most recent recordings of the National Oceanic and Atmospheric Association (NOAA), the Earth’s ten hottest years ever recorded all have occurred since 1997. (Sources: Global Surface Temperature Anomalies; NOAA National Climatic Data Center.)
3. Sea level may rise considerably. Sea level could rise 2.6 feet by the end of the century; and could rise as much as 6.6 feet. (Source: Pfeffer WT, Harper JT, O’Neel S. 2008. Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise. Science. 321 (5894): 1340-1343.)
4. Arctic ice is shrinking faster than expected. Current observations of Arctic sea ice show a much steeper drop in ice area than previously expected. 2007 had the lowest summer sea ice area since satellite observations began. (Source: Stroeve J, Serreze M, Drobot S, Gearheard S, Holland M, Maslanik J, Meier W,  Scambos T. 2008. Arctic Sea Ice Area Plummets in 2007. Eos, Transactions, American Geophysical Union. 89: 13-20.)
5. The effects of CO2 will be felt for generations. Studies indicate that even after excess human-caused CO2 emissions stop, the planet will experience the resulting warming for at least a thousand years. (Source: Solomon S, Plattner GK, Knutti R, Friedlingstein P. 2009. Irreversible climate change due to carbon dioxide emissions. Proceedings of the National Academy of Sciences. 106: 1704–1709.)
6. The economic impacts of climate change may be severe. If no action is taken to address human emissions of greenhouse gasses, the consequences could cost as much as 20% of world GDP. (Source: Stern N. (2007). Stern Review on The Economics of Climate Change. Executive Summary. HM Treasury, London)

Got questions about climate change?

Some consider climate change to be a debatable political issue rather than consensus science, and public disagreements have muddled the waters about the science behind climate change. This third-party independent site lists and considers common questions of those skeptical of climate change, cites the relevant science, and is an excellent resource to further understand the science and misconceptions around climate change. Please let us know if you have questions that aren't covered.