Query: The long-term correlation between CO2 and temperature is well established.

Relevant passages:
Climate change (general concept) <=SEP=> Climate variability includes all the variations in the climate that last longer than individual weather events, whereas the term climate change only refers to those variations that persist for a longer period of time, typically decades or more. In the time since the industrial revolution the climate has increasingly been affected by human activities that are causing global warming and climate change.The climate system receives nearly all of its energy from the sun. The climate system also radiates energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth\'s energy budget. When the incoming energy is greater than the outgoing energy, earth\'s energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.\nThe energy moving through Earth\'s climate system finds expression in weather, varying on geographic scales and time. Long-term averages and variability of weather in a region constitute the region\'s climate. Such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter the distribution of energy. Examples include variability in ocean basins such as the Pacific decadal oscillation and Atlantic multidecadal oscillation. Climate variability can also result from external forcing, when events outside of the climate system\'s components nonetheless produce changes within the system. Examples include changes in solar output and volcanism.\nClimate variability has consequences for sea level changes, plant life, and mass extinctions; it also affects human societies.

Ice core <=SEP=> An ice core is a core sample that is typically removed from an ice sheet , most commonly from the polar ice caps of Antarctica , Greenland or from high mountain glaciers elsewhere . As the ice forms from the incremental buildup of annual layers of snow , lower layers are older than upper , and an ice core contains ice formed over a range of years . The properties of the ice and the recrystallized inclusions within the ice can then be used to reconstruct a climatic record over the age range of the core , normally through isotopic analysis . This enables the reconstruction of local temperature records and the history of atmospheric composition .   Ice cores contain an abundance of information about climate . Inclusions in the snow of each year remain in the ice , such as wind-blown dust , ash , pollen , bubbles of atmospheric gas and radioactive substances . The variety of climatic proxies is greater than in any other natural recorder of climate , such as tree rings or sediment layers . These include ( proxies for ) temperature , ocean volume , precipitation , chemistry and gas composition of the lower atmosphere , volcanic eruptions , solar variability , sea-surface productivity , desert extent and forest fires .   The length of the record depends on the depth of the ice core and varies from a few years up to 800 kyr ( 800,000 years ) for the EPICA core . The time resolution ( i.e. the shortest time period which can be accurately distinguished ) depends on the amount of annual snowfall , and reduces with depth as the ice compacts under the weight of layers accumulating on top of it . Upper layers of ice in a core correspond to a single year or sometimes a single season . Deeper into the ice the layers thin and annual layers become indistinguishable .   An ice core from the right site can be used to reconstruct an uninterrupted and detailed climate record extending over hundreds of thousands of years , providing information on a wide variety of aspects of climate at each point in time . It is the simultaneity of these properties recorded in the ice that makes ice cores such a powerful tool in paleoclimate research .

Paleoclimatology <=SEP=> Paleoclimatology ( in British spelling , palaeoclimatology ) is the study of changes in climate taken on the scale of the entire history of Earth . It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within things such as rocks , sediments , ice sheets , tree rings , corals , shells and microfossils . It then uses the records to determine the past states of the Earth 's various climate regions and its atmospheric system . Studies of past changes in the environment and biodiversity often reflect on the current situation , specifically the impact of climate on mass extinctions and biotic recovery .

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 .