Climate change -- A geologic perspective.
Seasonal carbon dioxide levels in the atmosphere reached 400 ppm in May 2013. This represents a high point for the year
|A. General Aspects.|
|1. There have been several major ice ages throughout geological history due to the interplay between life, the carbon cycle, and climate.|
|1. Configuration of the continents (movement of tectonic plates) -- continents near the poles favor development of ice sheets.|
|2. Location of plates and related development of mountain belts in warm and humid climate zones favors enhanced chemical weathering.|
3. Changes in the Earth's orbit -- causes changes in the amount of energy absorbed by the surface of the Earth.
|Includes: Eccentricity (~100,000 year cycle), changes in the Tilt (~40,000 year cycle), Precession or the rotation axis (~23,000 year cycle).|
|4. Changes in ocean circulation. Here is a very nice animation model from NASA. This animation from NASA includes more of the complexities of surface ocean movement and wind interactions.|
|5. Changes in the composition of the atmosphere -- greenhouse gases (water, carbon dioxide, methane)|
C. Interrelationships: Global climate is complex -- there are many feedback mechanisms (both positive and negative) and some parameters amplify others (e.g. Greenhouse gases can increase after warming is initiated by changes in the Earth's orbit and amplify the resulting global warming). Here is a great series of web pages that explain factors that play roles in climate change from NASA. Here is a great set of resources from the National Oceanic and Atmospheric Administration (NOAA).
Surface water productivity as shown by chlorophyll concentration (red colors represent high concentrations and blue represents low ones) in the surface ocean. Measured by the SeaWIFS, photo from NASA's Web site.
|Here is a great video that summarizes how changes in the Earth's orbit initiated warming to bring the Earth out of ice ages; greenhouse gases amplify this effect. Global warming today is not related to orbital changes in solar energy input and is due to addition of carbon dioxide that is warming the climate today.|
Global Climate is getting warmer:
The map of the world on the right shows the temperature anomalies (red colors are warmer, blue ones are colder) relative to the 30-year period 1951-1980. From NASA: http://earthobservatory.nasa.gov/IOTD/view.php?id=47628&src=eoa-iotd (accessed Dec. 14, 2010.
See this link to compare temperature anomalies by decade since 1880.
People who doubt that global warming is occurring cite the evidence of "urban heat islands". They say that instrumental temperature records are biased toward data gathered in and near cities, which are warmer than the surrounding area. A recent study, however, has shown this to be untrue, and that the temperature record presented by NASA, NOAA, and other sources around the world are correct. Dark city roofs and parking lots can be significantly hotter than surrounding areas, but the urban island effect has not played a significant role in global temperature data.
Here is a good summary of this discussion. Dr. Richard Muller, a climate change skeptic, conducted an independent assessment of the global temperature instrument record and found that there is no "urban heat island" effect on the data.
What we know:
See this article for a meteorologist 's view of extreme weather and climate change.
The graph above is from a display at the Birch Aquarium at Scripps Oceanographic Institution in San Diego. It shows the concentration of carbon dioxide in the Earth's atmosphere over the last 500,000 years. Here is a link to a nice video from the Birch Aquarium that deals with global warming.
|* Good news on the greenhouse gas front: A recent study showed that global reduction of CFC's (Chlorofluorocarbons), which are very strong greenhouse gases is resulting in lower levels of global warming. CFC's were very widely used as refrigerants and propellants in spray cans and were banned in 1989 by the Montreal Protocol to protect the world's protective ozone layer in the upper atmosphere.|
Can Sunspot Activity Explain Global Warming?
People are entitled to their own beliefs, but not their own facts. Sunspots are dark areas that represent zones marked by intense magnet fields on the sun's surface and are often accompanied with faculae, which are very bright areas. Both are more abundant during times of increased solar activity, but the effect on global climate, although likely small, is not straight forward. Solar activity has varied over time, and some variations in the past have occurred with times of climate change, but sunspot activity has decreased over the last 30 years -- while global temperature has been increasing:
Here is the bottom line regarding sunspots and global climate change from the Skeptical Science web page (accessed Dec. 2, 2010).
Scientists believe that we are entering minimum period (Grand Minimum) of activity that has not occurred since about 300 years ago. This time, however, human-driven climate global warming will probably mean that the sunspot minimum will not result in global cooling.
Press sources often try to be "fair and balanced" -- but end up giving equal time to unsupported, wild competing ideas. Here is a 2004 story aired by the British Broadcasting News service that presents a contradictory view of sunspot influences on global climate. It first suggests that sunspot activity may be causing global climate change, but then at the end of the article the author states that sunspot activity does not correlate to global temperature rise in the last 20 years. "Over the past 20 years, however, the number of sunspots has remained roughly constant, yet the average temperature of the Earth has continued to increase."
Here is another good web site to check out sunspots and their effect on climate; here is another assessment of solar cycles and climate change, and here is another.
Here is an article that discusses the fact that the lower atmosphere (troposphere) is warming while the upper atmosphere (stratosphere) is cooling, which suggests that greenhouse warming, and not sunspot activity, is causing global warming.
Productivity in the Gulf of Mexico as shown by the chlorophyll concentration (red colors represent high concentrations and blue represents low ones) in the surface water. Photo from NASA's SeaWIFS satellite page,
|Here is a YouTube video that presents a simple explanation of the global carbon cycle.|
News organizations are often involved in trying confuse (mislead) people about climate science. Here is another example.
|Misleading the public (probably to get higher ratings) has become very common, and not just in the area of climate science. See this recent summary or the complete report from the World Public Opinion organization at the University of Maryland that documents the level of misunderstanding in Fall 2010. See also: http://www.youtube.com/watch?v=LJox3lZGNgg|
|Misleading the public has important implications beyond issues of climate. See this University of Maryland Program on International Policy Attitudes report about news sources and misconceptions.|
|Here is a great presentation by Dr. Naomi Oreskes on America and climate change denial. Note that this is an hour-long presentation, but is well worth the time.|
|Check out this NASA article that discusses increased melting on Greenland|
|Here is a good video on retreat of Arctic sea ice.|
|From NASA in 2006: Greenland is losing ice much faster than previously thought.|
|Methane Hydrates on the Sea Floor.|
|See this site by the U.S. Naval Research Laboratory Seafloor Sciences Branch for information about methane hydrates.|
|To check out climate change on many different time scales explore this site: NOAA Paleoclimatology Programs NEW Climate Time Line Information Tool Web site:|
|NASA's SeaWIFS Satellite Images of Oceanic Productivity|
|NOAA El Niño Page|
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