Query: Models are too sensitive to increases in carbon dioxide concentrations in the atmosphere, he said.

Relevant passages:
Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

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 .