Current Climate Change
Global Warming and Rising CO2
Global average surface temperatures have increased markedly over the last century (Figure 1). Humans have been measuring temperature directly since the mid- 1800's; these measurements show that temperature increased by 1.33°F (0.74°C ) between 1906 and 2005, and that the rate of warming is increasing (IPCC 2007a Ch.3). The decade from January 2000 to December 2009 was the warmest decade during this time period (NASA 2011). Although 1.33°F may not seem like a large temperature change, on a global scale this has huge implications for many of the earth's processes that affect ecosystems and humans. To put the number in perspective, many scientists think that temperature increases in excess of 3.6°F (2.0°C) relative to 1980-1999 will result in 'dangerous' climate change; others say that even lesser increases would be enough to create outcomes dangerous to human civilization (Anderson & Bows, 2011).
Excess greenhouse gases in the atmosphere are a measureable and significant contributor to global warming, and their concentrations have steadily increased over the past century (IPCC 2007). Carbon dioxide (CO2) , the most important greenhouse gas in terms of climate change, has been measured directly since 1958. Additionally, atmospheric levels of CO2 can be reconstructed for hundreds of thousands of years into the past using methods such as analyzing air bubbles trapped in ice. CO2 concentration in late 2011 was at 391 parts per million, a level that is higher than at any point during the past 800,000 years (Global Carbon Project 2011; Figure 2). Growth rates of atmospheric CO2 are still high, with 2010 experiencing one of the largest annual growth rates of the past decade (Global Carbon Project 2011).
For an animated look at how CO2 concentrations have changed over the last 800,000 years, see this video created by the NOAA Earth System Research Laboratory
Rising global temperatures are causing the Earth's climate patterns to change. Climate can be defined as the "average weather," or the average long-term (multi-decadal) meteorological conditions and patterns for a given area. Changes in climate that are occurring as the planet warms include seasonal and regional changes in temperature and precipitation, (USGCRP 2009, IPCC 2007a Ch.3), and increasing extreme weather events (IPCC 2011). As an example, precipitation from 1900 to 2005 increased significantly in some areas (eastern parts of North and South America, northern Europe and northern and central Asia), and declined in other regions during the same time period (the Sahel, the Mediterranean, southern Africa and parts of southern Asia - IPCC 2007a Ch.3).
In conjunction with climate change, during the 20th century there has been a nearly worldwide reduction in glacial mass and extent, a decrease in snow cover in many Northern Hemisphere regions, a decrease in Arctic sea ice thickness and extent, a decrease in the length of river and lake ice seasons, permafrost warming (IPCC 2007a Ch.4), warmer ocean temperatures, and rising sea levels (IPCC 2007a Ch.5), among other observed changes (Figure 3).
For up-to-date information on temperature, carbon dioxide, and other indicators of a warming planet, see the NASA Global Climate Change - Key Indicators page
Need more information?
See the following primers and resources for more introductory information on climate change.
Climate Change Resource Center:
United States Global Change Research Program:
Global Climate Change Impacts in the United States
The US EPA
Climate Change Science Facts
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Wanner, H.; Beer, J.; Butikofer, J.; Crowley, T.J.; Cubasch, U.; Fluckiger, J.; Goosse, H.; Grosjean, M.; Joos, F.; Kaplan, J.O.; Kuttel,M.; Muller, S.A.; Prentice, C.; Solomina, O.; Stocker, T.F.; Tarasov, P.; Wagner,M.; Widmann, M. 2008. Mid- to Late Holocene climate change: an overview. Quaternary Science Reviews. 27: 1791-1828.
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