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[[Image:NASA-1024x933.jpg|thumb|right|A composite map of [[Antarctica]] showing areas of greatest warming in red. The Wilkins Ice Shelf lies off the peninsula in the top left corner, and shows extensive warming. Overall, Antarctica shows little warming, and many areas to the  East (right) are almost cooling.<ref>Roberts, Greg (April 18, 2009). [http://www.news.com.au/antarctic-ice-is-growing-not-melting-away/story-0-1225700043191 "Antarctic ice is growing, not melting away."] News.com.au.  Retrieved on September 25, 2014.</ref>]]

[[Image:NASA-1024x933.jpg|thumb|right|A composite map of [[Antarctica]] showing areas of greatest warming in red. The Wilkins Ice Shelf lies off the peninsula in the top left corner, and shows extensive warming. Overall, Antarctica shows little warming, and many areas to the  East (right) are almost cooling.<ref>Roberts, Greg (April 18, 2009). [http://www.news.com.au/antarctic-ice-is-growing-not-melting-away/story-0-1225700043191 "Antarctic ice is growing, not melting away."] News.com.au.  Retrieved on September 25, 2014.</ref>]]

'''Anthropogenic global warming''' (AGW) is a theory that suggests that human activity is causing the Earth to warm. The theory posits that greenhouse gases, including carbon dioxide, methane, nitrous oxide, and water vapor, trap solar warmth on the planet. Computer models suggest that industrial and vehicular emissions could lead to catastrophic warming in the near future. Some use this theory as a basis to propose cuts in energy production and consumption.

'''Anthropogenic global warming''' (AGW) is a theory that suggests that human activity is causing the Earth to warm. The theory posits that greenhouse gases, including carbon dioxide, methane, nitrous oxide, and water vapor, trap solar warmth on the planet. Computer models suggest that industrial and vehicular emissions could lead to catastrophic warming in the near future. Some leftists use this theory as a basis to propose cuts in energy production and consumption and promote de-industrialization.

A reanalysis of weather station data for 1943 to 2012 by U.S. climate researcher Roy Spencer shows that after a cooler period in the 1960s and 1970s, U.S. temperatures returned to their earlier level.<ref name="Spencer" /> There are also temperature records based on weather balloon data and satellite readings, but these records do not go back far enough to reveal the full temperature cycle. Although recent climate trends are much discussed in the media, the temperature shifts that have been recorded are modest and should not be conflate with the various climate doomsday scenarios, which are based on computer modelling.

A reanalysis of weather station data for 1943 to 2012 by U.S. climate researcher Roy Spencer shows that after a cooler period in the 1960s and 1970s, U.S. temperatures returned to their earlier level.<ref name="Spencer" /> There are also temperature records based on weather balloon data and satellite readings, but these records do not go back far enough to reveal the full temperature cycle. Although recent climate trends are much discussed in the media, the temperature shifts that have been recorded are modest and should not be conflate with the various climate doomsday scenarios, which are based on computer modelling.

*'''Carbon dioxide is insignificant as a greenhouse gas.''' The level of CO₂ in the Earth's atmosphere is only 400 parts per million. Ninety to 95 percent of the greenhouse effect is due to water vapor.<ref>Friedenreich and Ramaswamy, "Solar Radiation Absorption by Carbon Dioxide, Overlap with Water, and a Parameterization for General Circulation Models," Journal of Geophysical Research 98 (1993):7255-7264)</ref> The Intergovernmental Panel on Climate Change (IPCC) claims that water vapor acts as a "positive feedback," i.e. warming creates more humidity, which leads to additional warming. There are humidity measurements going back to 1948, and they show no upward trend.<ref>"[https://wattsupwiththat.com/global-climate/ global climate]," ''Watt's Up with That''</ref> More humidity could lead to more clouds and therefore to cooling and to negative feedback. So why assume positive feedback? AGW works only if water vapor is a positive feedback, so that is what the IPCC must claim.<br/>Although Obama has denounced elevated carbon dioxide levels as "carbon pollution," greenhouse operators commonly increase the level of CO₂ to 1,000 ppm or more to enhance plant growth.<ref>"[https://www.sciencedaily.com/releases/2015/12/151210101819.htm Plant growth enhanced by increased carbon dioxide, but food webs give rise to significant variations]", ''Science News'', December 10, 2015.<br/>Harrison H. Schmitt and William Happer, "[http://arizonaskywatch.com/article/articles/In%20defense%20of%20carbon%20dioxide.pdf In Defense of Carbon Dioxide]," ''Wall Street Journal'', May 8, 2013.</ref>

*'''Carbon dioxide is insignificant as a greenhouse gas.''' The level of CO₂ in the Earth's atmosphere is only 400 parts per million. Ninety to 95 percent of the greenhouse effect is due to water vapor.<ref>Friedenreich and Ramaswamy, "Solar Radiation Absorption by Carbon Dioxide, Overlap with Water, and a Parameterization for General Circulation Models," Journal of Geophysical Research 98 (1993):7255-7264)</ref> The Intergovernmental Panel on Climate Change (IPCC) claims that water vapor acts as a "positive feedback," i.e. warming creates more humidity, which leads to additional warming. There are humidity measurements going back to 1948, and they show no upward trend.<ref>"[https://wattsupwiththat.com/global-climate/ global climate]," ''Watt's Up with That''</ref> More humidity could lead to more clouds and therefore to cooling and to negative feedback. So why assume positive feedback? AGW works only if water vapor is a positive feedback, so that is what the IPCC must claim.<br/>Although Obama has denounced elevated carbon dioxide levels as "carbon pollution," greenhouse operators commonly increase the level of CO₂ to 1,000 ppm or more to enhance plant growth.<ref>"[https://www.sciencedaily.com/releases/2015/12/151210101819.htm Plant growth enhanced by increased carbon dioxide, but food webs give rise to significant variations]", ''Science News'', December 10, 2015.<br/>Harrison H. Schmitt and William Happer, "[http://arizonaskywatch.com/article/articles/In%20defense%20of%20carbon%20dioxide.pdf In Defense of Carbon Dioxide]," ''Wall Street Journal'', May 8, 2013.</ref>

*'''The Earth has warmed or cooled many times. Historically, warm periods are associated with favorable climate.''' The [[Roman Warm Period]] (250 BC to 400 AD) was followed by the Dark Ages Cold Period (450-950 AD).<ref>"[http://www.co2science.org/subject/d/summaries/dacpeurope.php Dark Ages Cold Period (Europe) - Summary]", ''CO₂ Science'', 1 June 2005.</ref> The Medieval Warm Period lasted from 900 to 1300. From the 14th century to the early 19th century, there was a Little Ice Age.<ref>Bastasch, Michael, "[http://dailycaller.com/2013/12/13/study-earth-was-warmer-in-roman-medieval-times/ Study: Earth was warmer in Roman, Medieval times]", ''The Daily Caller''. For a peer-reviewed paper, see Moberg, A., et al. 2005 "[ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/moberg2005/nhtemp-moberg2005.txt 2,000-Year Northern Hemisphere Temperature Reconstruction]", ''World Data Center for Paleoclimatology''. The Moberg data set is charted [https://i0.wp.com/i90.photobucket.com/albums/k247/dhm1353/Moberg-1.png here].</ref>

*'''The Earth has warmed or cooled many times. Historically, warm periods are associated with favorable climate.''' The [[Roman Warm Period]] (250 BC to 400 AD) was followed by the Dark Ages Cold Period (450-950 AD).<ref>"[http://www.co2science.org/subject/d/summaries/dacpeurope.php Dark Ages Cold Period (Europe) - Summary]", ''CO₂ Science'', 1 June 2005.</ref> The Medieval Warm Period lasted from 900 to 1300. From the 14th century to the early 19th century, there was a Little Ice Age.<ref>Bastasch, Michael, "[http://dailycaller.com/2013/12/13/study-earth-was-warmer-in-roman-medieval-times/ Study: Earth was warmer in Roman, Medieval times]", ''The Daily Caller''. For a peer-reviewed paper, see Moberg, A., et al. 2005 "[ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/moberg2005/nhtemp-moberg2005.txt 2,000-Year Northern Hemisphere Temperature Reconstruction]", ''World Data Center for Paleoclimatology''. The Moberg data set is charted [https://i0.wp.com/i90.photobucket.com/albums/k247/dhm1353/Moberg-1.png here].</ref>

*'''For some, the attraction of the theory is that it supports their agenda.''' The environmentalist agenda of renewables, solar energy, conservation, and world government was put together in the 1970s in response to the energy crisis and to the overpopulation scare. At that time, most scientists thought the Earth was cooling.<ref>"[http://realclimatescience.com/the-corrupt-history-of-nasa-temperature-history/ The corrupt history of NASA temperature history]", ''Real Climate Science''.</ref><ref name="Time" /> When AGW came along, it was treated as an additional justification for this agenda.<br/>Steven Schneider, founding father of the AGW movement, was a global cooling believer in the early 1970s. "We have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we might have," he explained.<ref>This is from an article Schneider wrote for ''Discover'' magazine in 1989.[http://www.creationworldview.org/articles_view.asp?id=67]</ref> To Schneider, global cooling and global warming were just two "scary senarios." He could offer up whichever one was expedient.<br/>If the problem was simply too much carbon dioxide in the atmosphere, this could be addressed by promoting plant growth in the oceans.<ref>Carrington, Damian, "[https://www.theguardian.com/environment/2012/jul/18/iron-sea-carbon Dumping iron at sea can bury carbon for centuries, study shows]" ''The Guardian'', 18 July 2012.</ref> Such "geoengineering" doesn't appeal to liberals because AGW is less about the climate than about justifying the anti-energy cause. Scratch an AGW believer and there is an overpopulationist or a world government socialist underneath.

*'''For leftists, the attraction of the theory is that it supports their agenda.''' The environmentalist agenda of renewables, solar energy, conservation, and world government was put together in the 1970s in response to the energy crisis and to the overpopulation scare. At that time, most scientists thought the Earth was cooling.<ref>"[http://realclimatescience.com/the-corrupt-history-of-nasa-temperature-history/ The corrupt history of NASA temperature history]", ''Real Climate Science''.</ref><ref name="Time" /> When AGW came along, it was treated as an additional justification for this agenda.<br/>Steven Schneider, founding father of the AGW movement, was a global cooling believer in the early 1970s. "We have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts we might have," he explained.<ref>This is from an article Schneider wrote for ''Discover'' magazine in 1989.[http://www.creationworldview.org/articles_view.asp?id=67]</ref> To Schneider, global cooling and global warming were just two "scary senarios." He could offer up whichever one was expedient.<br/>If the problem was simply too much carbon dioxide in the atmosphere, this could be addressed by promoting plant growth in the oceans.<ref>Carrington, Damian, "[https://www.theguardian.com/environment/2012/jul/18/iron-sea-carbon Dumping iron at sea can bury carbon for centuries, study shows]" ''The Guardian'', 18 July 2012.</ref> Such "geoengineering" doesn't appeal to liberals because AGW is less about the climate than about justifying the anti-energy cause. Scratch an AGW believer and there is an overpopulationist or a world government socialist underneath.

*'''If the science was in fact settled, we would see less outrage at "deniers" and greater concern for scientific integrity.''' One climate science scandal after another has been exposed. No one's reputation is tarnished, no one pays any price. The first response of AGW backers is name calling and attempts to shut down the discussion. Argument is a last resort.<ref>Phil Plait, columnist for ''Discover'', is a good example. Scientific integrity in climate research? Plait has only contempt for those who pretends to care: "yawn," "non-event," etc. With no sense of irony, he can write, "these denialist claims are largely ad hominems." If you fail to show "the scientists" enough respect, then you are a "global warming denier." This name-calling-as-argument strategy is typical of AGW hacks. (Phil Plait, "[http://blogs.discovermagazine.com/badastronomy/2009/11/30/the-global-warming-emails-non-event/#.WHMkC9J97cs The global warming emails non-event]," ''Discover'',  November 30, 2009.)</ref> The logical explanation is that they already know AGW is a hoax, and they don't care.<br/>The Climategate emails show hoaxers scurrying to "hide the decline."<ref name=MISH>"[http://globaleconomicanalysis.blogspot.com/2009/11/hackers-prove-global-warming-is-scam.html#quEdWPhB8b6cs07f.99 Beware The Ice Age Cometh: Hackers Prove Global Warming Is A Scam]", ''MISH'S Global Economic Trend Analysis''</ref> The "hockey stick" view of climate history, which holds that global temperature was constant for 2,000 years and then surged in the last century, has been repeatedly debunked.<ref>Muller, Richard A., "[http://www.technologyreview.com/Energy/13830/ A Global Warming Bombshell]", ''Technology Review'' , Oct. 2004; calls into question famous graph by Michael Mann.</ref> It is a view at odds with several hypotheses considered well-established in this field, including the Medieval Warm Period<ref>John P. Rafferty, "[https://global.britannica.com/science/medieval-warm-period Medieval warm period (MWP)]", ''Britannica''</ref> and the Little Ice Age.<ref>John P. Rafferty, Stephen T. Jackson, "[https://global.britannica.com/science/Little-Ice-Age Little Ice Age (LIA)]", ''Britannica''.</ref><ref>See the graphs at "[http://www.climate4you.com/ Global temperatures]," Climate4you.</ref>  

*'''If the science was in fact settled, we would see less outrage at "deniers" and greater concern for scientific integrity.''' One climate science scandal after another has been exposed. No one's reputation is tarnished, no one pays any price. The first response of AGW backers is name calling and attempts to shut down the discussion. Argument is a last resort.<ref>Phil Plait, columnist for ''Discover'', is a good example. Scientific integrity in climate research? Plait has only contempt for those who pretends to care: "yawn," "non-event," etc. With no sense of irony, he can write, "these denialist claims are largely ad hominems." If you fail to show "the scientists" enough respect, then you are a "global warming denier." This name-calling-as-argument strategy is typical of AGW hacks. (Phil Plait, "[http://blogs.discovermagazine.com/badastronomy/2009/11/30/the-global-warming-emails-non-event/#.WHMkC9J97cs The global warming emails non-event]," ''Discover'',  November 30, 2009.)</ref> The logical explanation is that they already know AGW is a hoax, and they don't care.<br/>The Climategate emails show hoaxers scurrying to "hide the decline."<ref name=MISH>"[http://globaleconomicanalysis.blogspot.com/2009/11/hackers-prove-global-warming-is-scam.html#quEdWPhB8b6cs07f.99 Beware The Ice Age Cometh: Hackers Prove Global Warming Is A Scam]", ''MISH'S Global Economic Trend Analysis''</ref> The "hockey stick" view of climate history, which holds that global temperature was constant for 2,000 years and then surged in the last century, has been repeatedly debunked.<ref>Muller, Richard A., "[http://www.technologyreview.com/Energy/13830/ A Global Warming Bombshell]", ''Technology Review'' , Oct. 2004; calls into question famous graph by Michael Mann.</ref> It is a view at odds with several hypotheses considered well-established in this field, including the Medieval Warm Period<ref>John P. Rafferty, "[https://global.britannica.com/science/medieval-warm-period Medieval warm period (MWP)]", ''Britannica''</ref> and the Little Ice Age.<ref>John P. Rafferty, Stephen T. Jackson, "[https://global.britannica.com/science/Little-Ice-Age Little Ice Age (LIA)]", ''Britannica''.</ref><ref>See the graphs at "[http://www.climate4you.com/ Global temperatures]," Climate4you.</ref>