Query: When stomata-derived CO2 (red) is compared to ice core-derived CO2 (blue), the stomata generally show much more variability in the atmospheric CO2 level and often show levels much higher than the ice cores.

Relevant passages:
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 .

Greenhouse gas <=SEP=> A greenhouse gas ( abbrev . GHG ) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range . This process is the fundamental cause of the greenhouse effect . The primary greenhouse gases in Earth 's atmosphere are water vapor , carbon dioxide , methane , nitrous oxide , and ozone . Without greenhouse gases , the average temperature of Earth 's surface would be about -18 ° C , rather than the present average of 15 ° C . In the Solar System , the atmospheres of Venus , Mars and Titan also contain gases that cause a greenhouse effect .   Human activities since the beginning of the Industrial Revolution ( taken as the year 1750 ) have produced a 40 % increase in the atmospheric concentration of carbon dioxide , from 280 ppm in 1750 to 406 ppm in early 2017 . This increase has occurred despite the uptake of a large portion of the emissions by various natural `` sinks '' involved in the carbon cycle . Anthropogenic carbon dioxide emissions ( i.e. , emissions produced by human activities ) come from combustion of fossil fuels , principally coal , oil , and natural gas , along with deforestation , soil erosion and animal agriculture .   It has been estimated that if greenhouse gas emissions continue at the present rate , Earth 's surface temperature could exceed historical values as early as 2047 , with potentially harmful effects on ecosystems , biodiversity and the livelihoods of people worldwide . Recent estimates suggest that on the current emissions trajectory the Earth could pass a threshold of 2 ° C global warming , which the United Nations ' IPCC designated as the upper limit to avoid `` dangerous '' global warming , by 2036 .

Carbon dioxide in Earth's atmosphere <=SEP=> Carbon dioxide is an important trace gas in Earth 's atmosphere . Currently it constitutes about 0.041 % ( equal to 410 parts per million ; ppm ) by volume of the atmosphere . Despite its relatively small concentration is a potent greenhouse gas and plays a vital role in regulating Earth 's surface temperature through radiative forcing and the greenhouse effect . Reconstructions show that concentrations of in the atmosphere have varied , ranging from as high as 7,000 ppm during the Cambrian period about 500 million years ago to as low as 180 ppm during the Quaternary glaciation of the last two million years .   Carbon dioxide is an integral part of the carbon cycle , a biogeochemical cycle in which carbon is exchanged between the Earth 's oceans , soil , rocks and the biosphere . Plants and other photoautotrophs use solar energy to produce carbohydrate from atmospheric carbon dioxide and water by photosynthesis . Almost all other organisms depend on carbohydrate derived from photosynthesis as their primary source of energy and carbon compounds .   The current episode of global warming is attributed to increasing emissions of and other greenhouse gases into Earth 's atmosphere . The global annual mean concentration of in the atmosphere has increased by more than 40 % since the start of the Industrial Revolution , from 280 ppm , the level it had for the last 10,000 years leading up to the mid-18th century , to 399 ppm as of 2015 . The present concentration is the highest in at least the past 800,000 years and likely the highest in the past 20 million years . The increase has been caused by anthropogenic sources , particularly the burning of fossil fuels and deforestation . The daily average concentration of atmospheric CO2 at Mauna Loa Observatory first exceeded 400 ppm on 10 May 2013 . It is currently rising at a rate of approximately 2 ppm/year and accelerating . An estimated 30 -- 40 % of the released by humans into the atmosphere dissolves into oceans , rivers and lakes , which contributes to ocean acidification .