Query: “We indicated 23 years ago — in our 1994 Nature article — that climate models had the atmosphere’s sensitivity to CO2 much too high,” Christy said in a statement.

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James Hansen <=SEP=> James Edward Hansen ( born 29 March 1941 ) is an American adjunct professor in the Department of Earth and Environmental Sciences at Columbia University . He is best known for his research in climatology , his 1988 Congressional testimony on climate change that helped raise broad awareness of global warming , and his advocacy of action to avoid dangerous climate change . In recent years he has become a climate activist to mitigate the effects of climate change , on a few occasions leading to his arrest .   In 2000 , Hansen advanced an alternative view of global warming over the last 100 years , arguing that during that time frame the negative forcing via aerosols and the positive forcing via largely balanced each other out , and that the 0.74 ± 0.18 ° C net rise in average global temperatures could mostly be explained by greenhouse gases other than carbon dioxide , such as methane and chlorofluorocarbons . However , even then he wrote `` the future balance of forcings is likely to shift toward dominance of CO2 over aerosols ''

Climate sensitivity <=SEP=> Climate sensitivity is the equilibrium temperature change in response to changes of the radiative forcing . Therefore , climate sensitivity depends on the initial climate state , but potentially can be accurately inferred from precise palaeoclimate data . Slow climate feedbacks , especially changes of ice sheet size and atmospheric CO2 , amplify the total Earth system sensitivity by an amount that depends on the time scale considered .   Although climate sensitivity is usually used in the context of radiative forcing by carbon dioxide ( CO2 ) , it is thought of as a general property of the climate system : the change in surface air temperature ( ΔTs ) following a unit change in radiative forcing ( RF ) , and thus is expressed in units of ° C / ( W/m2 ) . For this to be useful , the measure must be independent of the nature of the forcing ( e.g. from greenhouse gases or solar variation ) ; to first order this is indeed found to be so .   The climate sensitivity specifically due to is often expressed as the temperature change in ° C associated with a doubling of the concentration of carbon dioxide in Earth 's atmosphere .   For coupled atmosphere-ocean global climate models ( e.g. CMIP5 ) the climate sensitivity is an emergent property : it is not a model parameter , but rather a result of a combination of model physics and parameters . By contrast , simpler energy-balance models may have climate sensitivity as an explicit parameter .   The terms represented in the equation relate radiative forcing ( RF ) to linear changes in global surface temperature change ( ΔTs ) via the climate sensitivity λ .   It is also possible to estimate climate sensitivity from observations ; however , this is difficult due to uncertainties in the forcing and temperature histories .

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 .