Editing Keeling Curve (section)

==Results and interpretation==
The measurements collected at [[Mauna Loa Observatory]] show a steady increase in mean atmospheric CO<sub>2</sub> concentration from 313 parts per million by volume ([[Parts-per notation|ppm]]) in March 1958 to 406 [[Parts-per notation|ppm]] in November 2018,<ref name="MaunaMonthly">{{cite web|title=Recent Monthly Average Mauna Loa CO2|url=http://www.esrl.noaa.gov/gmd/ccgg/trends/|website=Earth System Research Laboratory|access-date=9 May 2016}}</ref> with a current increase of 2.48 ± 0.26 (mean ± 2 std dev) [[Parts-per notation|ppm]] CO<sub>2</sub> per year.<ref name="Atmospheric Carbon Dioxide Growth Rate">{{cite web | url=http://mlg.eng.cam.ac.uk/carl/words/carbon.html | title=Atmospheric Carbon Dioxide Growth Rate | author=Rasmussen, Carl Edward}}</ref> This increase in atmospheric CO<sub>2</sub> is due to the [[combustion]] of [[fossil fuel]]s, and has been accelerating in recent years.  Since CO<sub>2</sub> is a [[greenhouse gas]], this has significant implications for [[global warming]]. Measurements of CO<sub>2</sub> concentration in ancient [[air bubble]]s trapped in polar [[ice core]]s show that mean atmospheric CO<sub>2</sub> concentration was between 275 and 285 [[Parts-per notation|ppm]] during the [[Holocene]] epoch (9,000 [[Common Era|BCE]] onwards), but started rising sharply at the beginning of the nineteenth century.<ref name="Neftel">{{cite journal|last1=Neftel|first1=A.|last2=Moor|first2=E.|last3=Oeschger|first3=H.|last4=Stauffer|first4=B.|date=1985|title=Evidence from polar ice cores for the increase in atmospheric CO<sub>2</sub> in the past two centuries|journal=Nature|volume=315|issue=6014|pages=45–47|bibcode=1985Natur.315...45N|doi=10.1038/315045a0|s2cid=4321970}}</ref>

The Keeling Curve also shows a cyclic variation of about 6 [[Parts-per notation|ppm]] each year corresponding to the seasonal change in uptake of {{CO2}} by the world's land vegetation. Most of this vegetation is in the [[Northern hemisphere]] where most of the land is located. From a maximum in May, the level decreases during the northern spring and summer as new [[plant]] growth takes {{CO2}} out of the atmosphere through [[photosynthesis]]. After reaching a minimum in September, the level rises again in the northern fall and winter as plants and leaves die off and decay, releasing {{CO2}} back into the atmosphere.<ref name=":0" /><ref name=":3" />