Query: While evidence that the earth’s orbital variations impact radiation levels and thus global temperatures does not of course mean that man is not in some way impacting the climate, studies like these highlight that the role man plays on the planet is dwarfed by natural phenomena utterly out of our control.

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Milankovitch cycles <=SEP=> Milankovitch cycles describes the collective effects of changes in the Earth 's movements on its climate over thousands of years . The term is named after Serbian geophysicist and astronomer Milutin Milanković . In the 1920s , he theorized that variations in eccentricity , axial tilt , and precession of the Earth 's orbit resulted in cyclical variation in the solar radiation ( insolation ) reaching the Earth , and that this orbital forcing strongly influenced climatic patterns on Earth .   The Earth 's orbit varies between nearly circular and mildly elliptical ( its eccentricity varies ) . When the orbit is more elongated , there is more variation in the distance between the Earth and the Sun , and in the amount of solar radiation , at different times in the year . In addition , the rotational tilt of the Earth ( its obliquity ) , which causes the seasons as the Earth revolves around the Sun , changes slightly . A greater tilt makes the seasons more extreme . Finally , the direction in the fixed stars pointed to by the Earth 's axis changes ( axial precession ) , while the Earth 's elliptical orbit around the Sun rotates ( apsidal precession ) . The combined effect of the two precessions is a cycle in which proximity to the Sun occurs during different astronomical seasons . If the Earth is closer to the Sun while the northern or southern hemisphere is tilted toward the Sun ( is in summer ) , then both effects work together to heat that hemisphere . If the Earth is further from the Sun during summer , the greater distance slightly reduces the heat of summer .   Similar astronomical theories had been advanced in the 19th century by Joseph Adhemar , James Croll and others , but verification was difficult because there was no reliably dated evidence , and because it was unclear which periods were important .   Now , materials on Earth that have been unchanged for millennia are being studied to indicate the history of Earth 's climate . A study of the chronology of Antarctic ice cores using oxygen-nitrogen ratios in air bubbles trapped in the ice , which appear to respond directly to the local insolation , concluded that the climatic response documented in the ice cores was driven by northern hemisphere insolation as proposed by the Milankovitch hypothesis . Analysis of deep-ocean cores and a seminal paper by Hays , Imbrie , and Shackleton provide additional validation of the Milankovitch hypothesis through physical artifacts . However , there are still several observations that the hypothesis does not explain .

Ice age <=SEP=> An ice age is a period of long-term reduction in the temperature of Earth 's surface and atmosphere , resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers . Within a long-term ice age , individual pulses of cold climate are termed `` glacial periods '' ( or alternatively `` glacials '' or `` glaciations '' or colloquially as `` ice age '' ) , and intermittent warm periods are called `` interglacials '' . In the terminology of glaciology , ice age implies the presence of extensive ice sheets in both northern and southern hemispheres . By this definition , we are in an interglacial period -- the Holocene -- of the ice age . The ice age began 2.6 million years ago at the start of the Pleistocene epoch , because the Greenland , Arctic , and Antarctic ice sheets still exist .

Global warming controversy <=SEP=> The global warming controversy concerns the public debate over whether global warming is occurring , how much has occurred in modern times , what has caused it , what its effects will be , whether any action should be taken to curb it , and if so what that action should be . In the scientific literature , there is a strong consensus that global surface temperatures have increased in recent decades and that the trend is caused by human-induced emissions of greenhouse gases . No scientific body of national or international standing disagrees with this view , though a few organizations with members in extractive industries hold non-committal positions . Disputes over the key scientific facts of global warming are more prevalent in the media than in the scientific literature , where such issues are treated as resolved , and such disputes are more prevalent in the United States than globally .   Political and popular debate concerning the existence and cause of climate change includes the reasons for the increase seen in the instrumental temperature record , whether the warming trend exceeds normal climatic variations , and whether human activities have contributed significantly to it . Scientists have resolved these questions decisively in favour of the view that the current warming trend exists and is ongoing , that human activity is the cause , and that it is without precedent in at least 2000 years . Public disputes that also reflect scientific debate include estimates of how responsive the climate system might be to any given level of greenhouse gases ( climate sensitivity ) , how global climate change will play out at local and regional scales , and what the consequences of global warming will be .   Global warming remains an issue of widespread political debate , often split along party political lines , especially in the United States . Many of the issues that are settled within the scientific community , such as human responsibility for global warming , remain the subject of politically or economically motivated attempts to downplay , dismiss or deny them -- an ideological phenomenon categorised by academics and scientists as climate change denial . The sources of funding for those involved with climate science -- both supporting and opposing mainstream scientific positions -- have been questioned by both sides . There are debates about the best policy responses to the science , their cost-effectiveness and their urgency . Climate scientists , especially in the United States , have reported official and oil-industry pressure to censor or suppress their work and hide scientific data , with directives not to discuss the subject in public communications . Legal cases regarding global warming , its effects , and measures to reduce it have reached American courts . The fossil fuels lobby has been identified as overtly or covertly supporting efforts to undermine or discredit the scientific consensus on global warming .