September 20, 2015

By Michael J. McGee

This story is told by numbers.  Earth's CO₂ crossover to 400 ppm CO₂ started in 2012 and it's not yet complete.  The crossover from the 300s started in the high northern latitudes where the greatest seasonal swings show up in the atmospheric CO₂ readings.  And it started with daily averages that are more variable than monthly and annual averages.

The table below is a kind of story teller.  It has 4 years, seven numbers, seven time periods, two locations and two scientific institutions.  Some of these elements are more important than others.  This small table tells a short story that provides a chance to gain some interesting and useful insights into the way the earth system works.  Atmospheric readings for CO₂ at one or two locations are globally and regionally signficant.  With atmospheric CO₂, you don't need a million data points to get an earth systems story.

Selected Milestones from Earth's
Crossover to 400 ppm CO₂

ppm = parts per milion

MLO = Mauna Loa Observatory
* Data from other northern latitudes has not been checked (e.g. Denmark and Finland).  It is posible that the first monthly average may have been recorded at a monitoring site other than Barrow, Alaska.

We're still waiting to see what happens when Scripps and NOAA post the annual average for 2015.  That could happen in the first couple of days or weeks of 2016.  But even if the 2015 average surpasses 400 ppm, Earth's 400 ppm CO₂ crossover is not over.  The 300s have started to dissapear from all the Mauna Loa records.  But for a few years still, they will continue to show up in some of the records at the more northern latitudes.

In time, the 400 ppm CO₂ crossover may happen in the other direction.  It is not known whether or when that will happen.  If it does, crossing back to levels below 400 ppm CO₂ will take much longer.  This is because the natural rate of decline is less than the current rate of human-caused increases.

September 20, 2015

 

By Michael J. McGee

 

This story is told by numbers.  Earth's CO₂ crossover to 400 ppm CO₂ started in 2012 and it's not yet complete.  The crossover from the 300s started in the high northern latitudes where the greatest seasonal swings show up in the atmospheric CO₂ readings.  And it started with daily averages that are more variable than monthly and annual averages.

The table below is a kind of story teller.  It has 4 years, seven numbers, seven time periods, two locations and two scientific institutions.  Some of these elements are more important than others.  This small table tells a short story that provides a chance to gain some interesting and useful insights into the way the earth system works.  Atmospheric readings for CO₂ at one or two locations are globally and regionally signficant.  With atmospheric CO₂, you don't need a million data points to get an earth systems story.

 

Selected Milestones from Earth's
Crossover to 400 ppm CO₂

ppm = parts per milion

Year	Date	Milestone for Atmospheric CO2	Data
2012	April	1st monthly average >400 ppm anywhere*	NOAA-Alaska: 400.01 ppm
2013	May 9	1st daily average >400 ppm at MLO	NOAA Media: 400.03 ppm Scripps Media: 400.08
2013	May 26-Jun 1 May 25-31	1st weekly average >400 ppm at MLO	NOAA: 400.01 ppm Scripps: 400.13 ppm
2014	April	1st monthly average >400 ppm at MLO	NOAA: 401.29 ppm Scripps: 401.33 ppm
2015?	Full Year	1st annual average >400 ppm at MLO	To be confirmed (or not) in January 2016

MLO = Mauna Loa Observatory
* Data from other northern latitudes has not been checked (e.g. Denmark and Finland).  It is posible that the first monthly average may have been recorded at a monitoring site other than Barrow, Alaska.

We're still waiting to see what happens when Scripps and NOAA post the annual average for 2015.  That could happen in the first couple of days or weeks of 2016.  But even if the 2015 average surpasses 400 ppm, Earth's 400 ppm CO₂ crossover is not over.  The 300s have started to dissapear from all the Mauna Loa records.  But for a few years still, they will continue to show up in some of the records at the more northern latitudes.

In time, the 400 ppm CO₂ crossover may happen in the other direction.  It is not known whether or when that will happen.  If it does, crossing back to levels below 400 ppm CO₂ will take much longer.  This is because the natural rate of decline is less than the current rate of human-caused increases.

 

400 PPM CO2 in Words

Beyond 400 PPM CO2 (Present Day)

CO2 Earth CO2 Records

2015

Wunderground   CO₂ bidding farewell to 400 ppm benchmark

Keeling Curve  Is this the last year below 400?

Climate Central  El Niño Could Push CO₂ Permanently Above Milestone

Climate Central  A global milestone: CO₂ passes 400 ppm

The Guardian  Global carbon dioxide levels break 400 ppm milestone

 

2014

Climate.gov  2013 State of the climate: Carbon dioxide tops 400 ppm

Climate Central  April will be first month with CO₂ levels aove 400 ppm

 

2013

Scripps UCSD  CO₂ at Mauna Loa reaches new milesone: Tops 400 ppm

NOAA  CO₂ at NOAA's Mauna Loa reaches new milestone: Tops 400 ppm

The Keeling Curve  What does 400 ppm look like?

Oceans at MIT  400 ppm CO2? Adding other GHGs equates to 478 ppm

NASA Global Climate Change  Ten NASA scientists talk of passing 400 ppm

 

2012

World Resources Institute  400 ppm: CO₂ levels cross sober new threshold

Yale e360  CO₂ milestone reached as levels hit 400 ppm across arctic

 

1979

Exxon (ICN source)  2010 projection of 400 ppm CO2 [ICN story]

 

 

400 PPM CO2 Video

 

2013

YouTube   Crossing 400: The Keeling Curve reaches a historic milestone