The state of the terrestrial atmosphere over the last ~10,000 years (Holocene), when conditions became amenable for agriculture and civilization, and over the preceding ~5 million years (Pliocene-Pleistocene) when prehistoric humans evolved, was constrained by a CO2 range of 180 to 300 ppm (click here), developed some 34 million years ago (end-Eocene) when atmospheric CO2 levels declined below 500 ppm (click here; click here) A rise of CO2 to 400 ppm at ~3.0 million years ago resulted in 2 - 3 degrees C temperature rise, melting of large parts of Greenland and Antarctic ice sheets and sea levels of +25+/-12 metres higher than the present (http://adsabs.harvard.edu/abs/2008EOSTr..89..501R).
Toward the end-20TH and early 21ST century Homo “sapiens” is realizing its carbon emissions, totaling over 300 billion tons (GtC) since 1750, and other forms of interference with the global natural system, are leading to sharp departure from the conditions which allowed its success on the planet, including rapid warming of the atmosphere to near +1.3 degrees C (partly masked by emitted aerosols) above pre-industrial levels and acidification of the oceans (decrease in pH by near-0.1) (click here), endangering the marine food chain.
Human inertia is paramount. Politics-as-usual and economics-as-usual can not argue with the laws of physics and chemistry, nor can they stop the climate from tracking toward increasingly dangerous states, likely approaching a tipping point of no return.
These efforts are backed by the pro-carbon emission ideology of the recent (8-10 March, 09) Heartland Institute conference in New York, titled “Global Warming: Was it Ever a Crisis” (click here click here linked to 50 or so think tanks which between them received $47 million in funds over the years from Exxon and the Koch and Scaife families, which made their first fortunes in the oil business (http://www.guardian.co.uk /environment/2009/mar/12/climate-change-sceptic-environment).
A principal think tank is the American Enterprise Institute (AEI), more than 20 of whose staff have worked as consultants to the Bush administration. The AEI has received more than $1.6 million from ExxonMobil and is offering scientists cash grants of $10,000 if they were prepared to dispute reports by the Intergovernmental Panel for Climate Change (IPCC) (http://www.guardian.co.uk/environment/2007/feb/02/frontpagenews. climatechange).
Blurring the boundaries with science fiction, climate “skeptics” have included the late Michael Crichton, author of the “State of Fear” and a friend of George W. Bush (http://www.nrdc.org/globalwarming/fcrichton.asp). Currently they include luminaries such as Czech president Vaclav Klaus, who regards environmentalism as the new face of communism, stating “I see the biggest threat to freedom, democracy, the market economy and prosperity now in ambitious environmentalism, not in communism” http://www.worldtribune.com/worldtribune/WTARC/2008/ss_ politics0228_06_10.asp; click here presumably defining "freedom" as the right to use the atmosphere as open sewer for carbon gases.
The scientific “star” of the Heartland conference is Richard Lindzen, an atmospheric scientist who regards Exxon as "the only principled oil and gas company I know in the US." (http://news.bbc.co.uk/2/hi/business/6595369.stm), and whose opinions are cited throughout the ExxonMobil funded groups and conferences organized by the company (click here Lindzen accuses school teachers asking questions about global warming as being “straight out of Hitlerjugen” (click here click here) Moving from denial to an attack on the scientific community, Lindzen stated: “endorsing global warming just makes their lives easier" (click here).
Oblivious to physics, chemistry and climate science, the principal weapon of climate “skeptics” remains ad-hominem slur (“Gore lied” http://algorelied.com/?p=630), conspiracy theories and ad-infinitum use of terms such as “alarmism” and even “ecofascism” (http://www.akpress.org/1996/items/ecofascism).
Some "skeptics" appear to confuse, or pretend to confuse, the weather with the climate, misunderstand meaning of terms such as “average” or “trend”, hinging their arguments on transient cooling events. Lately, based on the La Nina cooling phase since 2007, some claim global cooling (http://www.worldclimatereport.com/index.php/2007/03/16/the-coming-global-cooling/) (would have been nice).
Some "skeptics" (http://www.heartland.org/full/24809/Heartland_Institute_ Announces_Keynote_Speakers_For_International_Conference_On_Climate_Change.html) continue to claim climate change does not exist, or is caused by the sun (precise measurements of solar radiation disprove this theory), or by cosmic rays (which enhance clouding).
There are skeptics who argue that, since climate has always changed in the past, in particular during the glacial-interglacial cycles, 20th – 21st global warming is also of natural origin (http://www.smedg.org.au/plimer0701.html). They deny that warming since the outset of the industrial age, accelerating since about 1975 – 1976, represents the consequence of the emission of some 300 gigaton of carbon since about 1750. Some skeptics invoke the effects of solar radiation. However, whereas solar irradiance accounts for a rise by about 0.3-0.4 degrees during the first half of the 20th century, it stabilized from about 1970, following the 11 years sun-spot cycle which fluctuates within the range of +/-0.1 degrees C, while greenhouse-driven forcing rose by about +0.6 degrees C (Solanki, 2002:
click here Since 1750 the total rise in atmosphere energy due to solar radiation is estimated at 0.12 Watt/m2 while the anthropogenic factor, due to emissions and land clearing, is estimated at 1.6 Watt/m2 (IPCC-AR4-2007 figure SPM-2: http://ipcc-wg1.ucar.edu/wg1/wg1-report.html)
Some "skeptics" (http://masterresource.org/?p=1280) invoke water vapor as a cause of global warming (evaporation is but a feedback effect, and vapor levels iare very low over the fast warming poles and desert regions). Other (click here; point to the lag of CO2 rise behind temperatures during glacial age terminations which is due to the delay in the release of CO2 from the oceans and biosphere, which lags behind the rapid warming induced by the ice-water albedo flip, namely the change from reflecting ice sheets to infrared-absorbing open water).
Other skeptics (click here) claim global warming occurs on other planets and is thus of extraterrestrial origin (no inter-planetary connection is known), or even due to geothermal rise (click here) (the main connection of internal Earth processes is via volcanic eruptions).
Publishing in politically friendly media provides a golden opportunity to gain public exposure and air grudges against science and scientists. A hallmark of climate change skeptics is the dissemination of doubt (“doubt is our product”) (http://www.desmogblog.com/directory/vocabulary/4067) and a reluctance to engage in direct public discussions with climate scientists.
Attempts have been made to delete critical data sets, as in the film ”The Great Global Climate Swindle”, where mean global temperature data from the 1980s onward are not shown (click here; abc-australias-tony-jones-and-the-great-global-warming-swindle-debate/).