Arguments
Are CO2 levels increasing?
What the science says...
Currently, humans are emitting around 29 billion tonnes of carbon dioxide into the atmosphere per year. Around 43% remains in the atmosphere - this is called the 'airborne fraction'. The rest is absorbed by vegetation and the oceans. While there are questions over how much the airborne fraction is increasing, it is clear that the total amount of CO2 in the atmosphere is increasing dramatically. Current CO2 levels are the highest in 15 million years.
Climate Myth...
CO2 is not increasing
"...there is the contention by Wolfgang Knorr of the Department of Earth Sciences at the University of Bristol in England that carbon dioxide levels in the atmosphere are about where they were 160 years ago." (as quoted by Ken Ward Jr.)
The 'airborne fraction' refers to the amount of human CO2 emissions remaining in the atmosphere. Approximately 43% of our CO2 emissions stay in the atmosphere with the rest being absorbed by carbon sinks. But is the airborne fraction increasing? A paper published in November 2009 found no statistically significant trend (Knorr 2009). Anthony Watts labeled this result the "Bombshell from Bristol" - A potentially devastating result for anthropogenic global warming. Was it such a shock? The 2007 IPCC verdict on the airborne fraction was "There is yet no statistically significant trend in the CO2 growth rate since 1958 .... This 'airborne fraction' has shown little variation over this period." (IPCC AR4) I'm not sure the move from "not much happening" "to "still not much happening" warrants the label "bombshell".
The airborne fraction is calculated from the rate of human CO2 emissions and changes in atmospheric CO2 concentration. The global increase in atmospheric CO2 has been directly measured since 1959 and can be calculated from ice cores for earlier periods. Primarily, CO2 emissions come from fossil fuel combustion with a lesser contribution from land use changes. Fossil fuel combustion is calculated from international energy statistics. CO2 emissions from land-use changes are more difficult to estimate and come with greater uncertainty. Land use emissions are estimated using deforestation and other land-use data, fire observations from space and carbon cycle modeling.
There have been several recent studies determining the airborne fraction. Trends in the sources and sinks of carbon dioxide (Le Quere 2009) examines the airborne fraction from 1959 to 2008. This period was chosen as we have directly measured atmospheric CO2 levels over this time. Fossil fuel emissions rose steadily in recent decades, contributing 8.7 ± 0.5 gigatonnes of carbon in 2008. This is 41% greater than fossil fuel emissions in 1990. CO2 emissions from land use was estimated at 1.2 ± 0.4 gigatonnes of carbon in 2008. Note the proportionally higher uncertainty compared to fossil fuel emissions.
Over this period, an average of 43% of each year's CO2 emissions remained in the atmosphere although there is much year-to-year variability. The noise in the airborne fraction was reduced by removing the variability associated with El Nino Southern Oscillation (ENSO) and volcanic activity. They found the airborne fraction increased by 3 ± 2% per decade. This is a slightly increasing trend although only barely statistically significant .
Knorr 2009 extends this analysis back to 1850 by combining direct CO2 measurements from Mauna Loa and the South Pole with CO2 data derived from Antarctic ice cores. This enabled Knorr to compare CO2 emissions to atmospheric CO2 levels for the past 150 years.
Figure 1: Observed increase atmospheric CO2 derived from direct measurements, taking the average of Mauna Loa (Hawaii) and the South Pole (thin solid line) and two ice cores: Law Dome (dashed thin line) and Siple (thin dotted line). This is compared to total anthropogenic emissions (thick solid line) and 46% of total emissions (thick dashed line). (Knorr 2009)
Knorr finds that since 1850, the airborne fraction has eemained relatively constant. When CO2emissions were low, the amount of CO2absorbed by natural carbon sinks was correspondingly low. As human CO2 emissions sharply increased in the 20th Century, the amount absorbed by nature increased correspondingly. The airborne fraction remained level at around 43%. The trend since 1850 is found to be 0.7 ± 1.4% per decade.
There are several differences in methodology between Knorr 2009 and Le Quere 2009. Knorr's result does not include the filtering for ENSO and volcanic activity employed by Le Quéré. However, when Knorr does include this filtering in his analysis, he finds a trend of 1.2 ± 0.9% per decade. This is smaller than Le Quere's result but is statistically significant.
Knorr also finds the 150 year trend while Le Quéré looks at the last 50 years. This may be significant. If the airborne fraction is increasing, it is possibly a recent phenomenon due to natural carbon sinks losing their absorption ability after becoming saturated. Several studies have found recent drops in the uptake of CO2 by oceans (Le Quere 2007, Schuster 2007, Park 2008). However, with such a noisy signal, this is one question that will require more data before being more fully resolved.
Lastly, some perspective. There are still areas of uncertainty associated with the carbon cycle. Because of this uncertainty, scientists are currently debating whether the airborne fraction is steady at 43% or slightly Increasing from 43%. Unfortunately, some skeptics use this uncertainty to hold the position that the airborne fraction is closer to 0%.
Intermediate rebuttal written by John Cook
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Additional videos from the MOOC
Andy Skuce: The CO2 rise is man man-made
Interviews with various experts
Expert interview with Corinne Le Quéré
Last updated on 8 July 2015 by pattimer. View Archives
Ritchieb1234,
Searching at RealClimate using the keywords "temperature change emissions stop" gives several interesting hits. The first three or four are advertisements.
This OP from 2010 seems to describe what you seek. The original letter is here. Follow the citations at Google Scholar to get more recent ideas.
They have covered a lot of material in the old posts at Realclimate. They are probably at a technical level that you would like. Currently they post less because they have already covered so many issues.
"1) if CO2 emissions stopped today, what global average temperature would we eventually reach, and 2) how soon would we reach it?"
Good questions. Looking to the most recent summary at hand, Canada's Changing Climate Report for 2019:
Section 3.4:
And
Section 3.5:
Figure 3.9 shows the persistence of elevated temperatures after emissions cease:
As this is your first post, Skeptical Science respectfully reminds you to please follow our comments policy. Thank You!
Thank you for the membership, i have followed the mauna loa curve for years and wondered what the yearly dip in co2 increase is caused by.
This year the curve is straight up for the first time ever and i found a correlation; China.
Since 2020 i have taken dayly screenshots of the "windy" website which monitors the co2 levels globally and focussed on china's dayly output, in short it showed increased activity just before the chinese new year celebration ( 12 feb to 26 feb ) and continues during the celebrations because of the pandemic demand for products.
Mauna loa is directly downwind of china by some days and is in effect monitoring China's co2 output.
You can check this out for yourselves on the "windy.com" and the noaa mauna loa co2 graph websites.
Here is a link to my 3 youtube video's titled; "co2 levels explained"on youtube, it has all the info combined to show the relationship in detail on a day by day basis;
https://www.youtube.com/watch?v=kbjnbw_npY8
https://www.youtube.com/watch?v=2IYQZu-XwOc
https://www.youtube.com/watch?v=7szFJD9nAFM
Another significant indicator is the dip in 2008 which stopped China's output for two months in the mauna loa graph.
Thank you; the Inspector.
the Inspector @41,
I'm not at all convinced by your 'China' theory or even that there is a convincing 'dip' in MLO CO2 levels (or perhaps best described as "less of a February CO2 rise relative to consecutive months").
But I would draw your attention to a definite error in your argument. The reason the windy.com graphics are showing sky-high levels over China and very low levels elsewhere is because this is CO (carbon monoxide) being plotted in parts per billion. It is not showing CO2 (carbon dioxide).