Climate change is mostly a natural phenomenon, which scientists say has occurred in repeated cycles of cooling (see Ice Ages) and warming over millions of years. Yet many writers have been urging America to fund an ill-conceived initiative to "stop global warming", as if warmer nights or winters would make human life more difficult. The term "climate change" has largely replaced the term "global warming", in ideological discussions.
Ideologues insist that the world's top scientists have reached a "consensus" that most of the warming which land-based weather stations have recorded in the last century is due to human activity. The basis for this claim is a set of reports published by the IPCC, an agency of the United Nations. The assumption is that the government-appointed representatives who run the IPCC would be completely objective and neutral, and would place finding and revealing the truth ahead of any nationalistic interests.
A lot of money is spent publicizing each side's position in the debate:
- "Newsweek purports to take readers inside the world of “Global-Warming Deniers: A Well-Funded Machine” without mentioning that the global-warming alarmists are even better funded, in some cases with government support. 
Ideologues use all sorts of tricks to convince the general public to support them on the climate change issue. A perennial favorite is to trumpet the current year as the "warmest year on record", as if one outlier denotes a trend. Probably the most insidious kind of trick is to accuse objective people of cherry-picking and censorship, while hypocritically doing just that themselves.
The allegedly harmful effects of climate change include warming temperatures, changing weather patterns, an increase in sea level and in general any climate event affected by global warming. Climate change is one of the top environmental issues, with liberals and conservatives evenly divided on whether global warming is man-made or, if it is significantly occurring, is a natural event — along with global cooling.
Jack M. Hollander wrote:
- The planet has warmed since the mid-1800s, but before that it cooled for more than five centuries. Cycles of warming and cooling have been part of Earth's natural climate history for millions of years. So what is the global warming debate about? It's about the proposition that human use of fossil fuels has contributed significantly to the past century's warming, and that expected future warming may have catastrophic global consequences. But hard evidence for this human contribution simply does not exist; the evidence we have is suggestive at best. Does that mean the human effects are not occurring? Not necessarily. But media coverage of global warming has been so alarmist that it fails to convey how flimsy the evidence really is. Most people don't realize that many strong statements about a human contribution to global warming are based more on politics than on science. Indeed, the climate change issue has become so highly politicized that its scientific and political aspects are now almost indistinguishable. 
- What is the most important greenhouse gas?
- What is the role of clouds?
- What are the uncertainties in understanding climatic change?
- The UN's climate panel said recently there is a 90% chance that most of the last 50 to 100 years of global warming are due to human activity
- Sallie Baliunas points out that the same climate panel also said, "Our ability to quantify the human influence on global climate is limited because the expected signal is still emerging from the noise of natural variability, and because there are uncertainties in key factors" 
Many times, AGW advocates pay lip service to general principles which they themselves violate, while broadcasting false accusations that their opponents are violating these principles. The AGW side has made every effort to censor their opponents, heaping enormous pressure on scientists and other academics to silence them. Accordingly, the US media gave great publicity to James Hansen when he accused NASA of trying to silence him.
Environmentalism and climate change
- The earth's atmosphere warmed one or two degrees Fahrenheit (0.8 Centigrade) during the 20th century.
- Most of this warming is man-made.
- The warming is likely to continue and to be harmful to human, animal and plant life.
- We must all work together to stop it by reducing emission of greenhouse gases.
Science and climate change
Jack M. Hollander wrote:
... climate change remains a fascinating and important scientific subject. Climate dynamics and climate history are extraordinarily complex, and despite intensive study for decades, scientists are not yet able to explain satisfactorily such basic phenomena as extreme weather events (hurricanes, tornadoes, droughts), El Nino variations, historical climate cycles, and trends of atmospheric temperatures. The scientific uncertainties about all these matters are great, and not surprisingly, competent scientists disagree in their interpretations of what is and is not known.
William Happer wrote:
The current debates about global climate change are complicated by our not understanding the physics of the sun or of the earth’s atmosphere and oceans well enough to dismiss them as major causes of climate change on the earth. Dramatic climate changes like the medieval warm period at the time of the Viking settlements of Iceland and Greenland from about a.d. 900 to 1250, and the subsequent “little ice age,” from about 1250 to 1700, which led to extinction of the Greenland settlements, were certainly not caused by manmade changes in the concentration of carbon dioxide in the atmosphere.
One of the major problems with many scientists' conclusions about climate change is a misunderstanding of correlation versus causation. Some studies show correlations between increasing concentrations of atmospheric greenhouse gases and increasing precipitation, and between human activity and atmospheric greenhouse gases, and then go so far as to conclude that humans are causing increased rain, snow, and catastrophic flooding. Correlation does not imply causation. This is especially true considering the relatively short periods of data used (a few decades at most) compared to the Earth's age, and the fact that weather patterns have been cyclic throughout history (see climate cycles).
- http://goliath.ecnext.com/coms2/summary_0199-2875898_ITM Global Warming: Both Sides
- "Water vapor is the most important greenhouse gas ..." 
- Hansen "shot to fame when he accused the administration of trying to censor his views on climate change" 
- Gillis, Justin. "Study Links Rise in Rain and Snow to Human Actions." The New York Times, February 16, 2011. http://www.nytimes.com/2011/02/17/science/earth/17extreme.html?_r=2&ref=science
- Schiermeier, Quirin. "Increased Flood Risk Linked to Global Warming." 2011. Nature, Vol. 470, p. 316. http://www.nature.com/news/2011/110216/full/470316a.html