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 1.53°F (0.85°C ) between 1880 and 2012, and that the rate of warming is increasing (IPCC 2013 Ch. 2). With the exception of 1998, the 10 warmest years in the 134-year record all have occurred since 2000, with 2010 and 2005 ranking as the warmest years on record (NASA GIS 2014). Although 1.53°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 create outcomes dangerous to human civilization; others say that even lesser increases would be enough to do this (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 2013 Ch. 2). 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 2013 was at 395 parts per million, a level that is higher than at any point during the past 800,000 years (Global Carbon Budget 2014; Figure 2). Growth rates of atmospheric CO2are still high; CO2 emissions from fossil fuel burning and cement production in 2013 were the highest in any other year of human history, 61% higher than CO2 emissions in 1990 (Global Carbon Budget 2014).
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 2014 Ch. 2, IPCC 2013 Ch.2), and increasing extreme weather events (IPCC 2011). As an example, precipitation from 1991 to 2012 increased significantly in some parts of the United States including the Great Plains, Northeast, and Midwest, , and declined in other regions during the same time period, particularly parts of the Southwest and Southeast (USGCRP 2014 Ch. 2).
In conjunction with temperature and precipitation changes, during the 20th and early 21st centuries 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, warmer ocean temperatures, and rising sea levels (IPCC 2013 Summary for policymakers), among other observed changes (Figure 3).
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:
The Third National Climate Assessment
NASA Global Climate Change
Climate change: How do we know?
Center for Climate and Energy Solutions:
Climate Change – The Basics
Cooperative Institute for Research in Environmental Sciences:
Reading the IPCC Report - Recorded seminar series
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