Stanford Solar Center
About the SunFor StudentsFor EducatorsSpace Weather Monitors
Ancient ObservatoriesSolar FolkloreSolar Art & Literature

Global Warming -- Research Issues

Global Warming

Latest News

Solar Influences on Climate
(Latest research determines Sun is not the cause of global warming)

New Sunspot Count Techniques Rule Out Sun as Perpetrator of Global Warning

97% of Climate Science Papers Agree Warming is Man-Made

Translation into Portuguese provided by

What is it?

greenhouse gases in the Earth's atmosphere
Graphics from Intergovernmental Panel on Climate Change Report Summary

Global Warming -- a gradual increase in planet-wide temperatures -- is now well documented and accepted by scientists as fact. A panel convened by the U.S National Research Council, the nation's premier science policy body, in June 2006 voiced a "high level of confidence" that Earth is the hottest it has been in at least 400 years, and possibly even the last 2,000 years. Studies indicate that the average global surface temperature has increased by approximately 0.5-1.0°F (0.3-0.6°C) over the last century. This is the largest increase in surface temperature in the last 1,000 years and scientists are predicting an even greater increase over this century. This warming is largely attributed to the increase of greenhouse gases (primarily carbon dioxide and methane) in the Earth's upper atmosphere caused by human burning of fossil fuels, industrial, farming, and deforestation activities.

Average global temperatures may increase by 1.4-5.8ºC (that's 2.5 - 10.4º F) by the end of the 21st century. Although the numbers sound small, they can trigger significant changes in climate. (The difference between global temperatures during an Ice Age and an ice-free period is only about 5ºC.) Besides resulting in more hot days, many scientists believe an increase in temperatures may lead to changes in precipitation and weather patterns. Warmer ocean water may result in more intense and frequent tropical storms and hurricanes. Sea levels are also expected to increase by 0.09 - 0.88 m. in the next century, mainly from melting glaciers and expanding seawater . Global Warming may also affect wildlife and species that cannot survive in warmer environments may become extinct. Finally, human health is also at stake, as global Climate Change may result in the spreading of certain diseases such as malaria, the flooding of major cities, a greater risk of heat stroke for individuals, and poor air quality.

Climate change is very likely having an impact now on our planet and its life, according to the latest installment of a report published by the Intergovernmental Panel on Climate Change (IPCC). And the future problems caused by rising seas, growing deserts, and more frequent droughts all look set to affect the developing world more than rich countries, they add. The report is the second chapter of the IPCC's Fourth Assessment -- the most comprehensive summary yet of research into the causes and effects of climate change. To read more, visit Effects of climate change tallied up.

Back to Top


Greenhouse Gases

The increase in greenhouse gases caused by human activity is often cited as one of the major causes of global warming. These greenhouse gases reabsorb heat reflected from the Earth's surface, thus trapping the heat in our atmosphere. This natural process is essential for life on Earth because it plays an important role in regulating the Earth's temperature. However, over the last several hundred years, humans have been artificially increasing the concentration of these gases, mainly carbon dioxide and methane in the Earth's atmosphere. These gases build up and prevent additional thermal radiation from leaving the Earth, thereby trapping excess heat.

Solar Variability & Global Warming

temperature, CO2, and sunspots During the initial discovery period of global climate change, the magnitude of the influence of the Sun on Earth's climate was not well understood. Since the early 1990s, however, extensive research was put into determining what role, if any, the Sun has in global warming or climate change.

A recent review paper, put together by both solar and climate scientists, details these studies: Solar Influences on Climate. Their bottom line: though the Sun may play some small role, "it is nevertheless much smaller than the estimated radiative forcing due to anthropogenic changes." That is, human activities are the primary factor in global climate change.

sun image EIT Solar irradiance changes have been measured reliably by satellites for only 30 years. These precise observations show changes of a few tenths of a percent that depend on the level of activity in the 11-year solar cycle. Changes over longer periods must be inferred from other sources. Estimates of earlier variations are important for calibrating the climate models. While a component of recent global climate change may have been caused by the increased solar activity of the last solar cycle, that component was very small compared to the effects of additional greenhouse gases. According to a NASA Goddard Institute for Space Studies (GISS) press release, "...the solar increases do not have the ability to cause large global temperature increases...greenhouse gases are indeed playing the dominant role..." The effects of global climate change are apparent (see section below) despite the fact that the Sun is once again less bright during the present solar minimum. Since the last solar minimum of 1996, the Sun's brightness has decreased by 0.02% at visible wavelengths, and 6% at extreme UV wavelengths, representing a 12-year low in solar irradiance, according to this NASA news article (April 1, 2009). Also, be sure to read this more recent article: 2009: Second Warmest Year on Record; End of Warmest Decade.

Back to Top

Trends & Effects; Scientific Studies

climate change attribution- graph Image created by Robert A. Rohde / Global Warming Art

The United Nations Intergovernmental Panel on Climate Change has been studying global warming for years. Their most recent report, issed in February 2007, (see Climate Change 2007: The Physical Science Basis (summary for policymakers), U.N. Report Confirms Human Activity to Blame for Earth's Warming Climate (from Voice of America), and Intergovernmental Panel on Climate Change), concludes that "The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous exide are primarily due to agriculture." The report goes on to note that these findings come with a "very high confidence rate [words emphasized in italics in the report summary] that the globally averaged net effect of human activities since 1750 has been one of warming."

The primary place where scientific studies related to global climate change are reported is the American Geophysical Union (AGU). Based on the outcome from a considerable number of studies in various fields related to global climate change, the AGU has issued a statement: Society Must Address the Growing Climate Crisis Now.

The American Meteorological Society, which promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences, has also issued a statement on global changes.

Additional discussion on current and potential future effects and feedback mechanisms can be found here: Effects of global warming.

Back to Top

Frequently Asked Questions
  1. Where is the data that show global warming is largely attributed to the increase of greenhouse gases (primarily carbon dioxide and methane) in the Earth's upper atmosphere caused by human burning of fossil fuels?

  2. To what extent does the Sun's variability affect and/or cause global climate change?

  3. My spiritual leaders disagree with the scientists, how do I determine whom to believe?

Back to Top

Where Do I Learn More?

The Role of the Sun in Climate Change by Douglas V. Hoyt and Kenneth Schatten; Oxford University Press, 1997. ISBN: 0195094131

"Plows, Plagues, and Petroleum: How Humans Took Control of Climate" by William F. Ruddiman; Princeton University Press (2005); ISBN: 0691121648

An excellent book, written by one of the world's top paleoclimatologists, but understandable to both scientist and nonscientists alike. Ruddiman summarizes, explains with research and facts, and places in context the influence of humans on atmospheric composition, climate and global warming. His focus is on the big picture -- changes to climate over the last 400,000 years with special attention to changes beginning 8,000 years ago. He makes only brief mention of solar variability as affecting climate (because his focus is on longer trends), but he does an excellent job of describing how small complications in the Earth's orbit cause regular glaciation on 100,000, 41,000, and 22,000 year timeframes. Note that a primary hypothesis of his book is the suggestion that early human agriculture started having an effect on the Earth's climate as early as 8,000 years ago. This is an intriguing idea which is still waiting for further scientific verification or discredit. However, the information in Ruddiman's book is still immensely useful in understanding current global warming and climate change.

"Ancient Observations Link Changes in Sun's Brightness and Earth's Climate" by Kevin D. Pang and Kevin K. Yao; EOS, Transactions of the American Geophysical Union, Volume 83, number 43, 22 October 2002, pages 481+.

This is an article written for scientists. The authors track 9 cycles of changes in solar brightness over the last 1800 years, and then correlate these with various changes in the Earth's climate. As you undoubtedly know, an especially suspicious correlation is that of a period of no sunspots (and hence low solar activity) corresponding with the Maunder Minimum of ~1645 to 1715 A.D, a period of extreme cold in Europe. Because of the complexity of effects on the Earth's climate, the jury is still out on whether this period of a Little Ice Age was indeed caused by the lack of solar activity. However, the correlations are intriguing and continue to be discussed at scientific meetings such as the AGU. You can find lots more about the Maunder Minimum and its relationship to sunspots on the web.

Back to Top

©2008 by Stanford SOLAR Center · Permitted Uses · Credits