2020 Mauna Loa CO2 levels

[Pmt111500]

Hi Stephan,

The error margins of your expectations are too small because often the next weeks' value doesn't fall in that range. I wouldn't mind if you would leave out the expectation altogether but others seem much into short-term guesses and forecasts and bets. But I like the weekly data!

At Mauns Loa and almodt all places elsewhere too, the weekly values depend much on weather. Various air masses carry slightly different amounts of CO2 and other ghgs, so accurate predictions should take this into account. For example, in spring time the most CO2 is seen in the Arctic/subarctic air masses and if Mauna Loa gets winds from north the expected values are often, even mostly over the average values. Later in the summer the difference isn't that big.

[oren]

I like the expectations because, successful or not, they help show the uncertainty.

[Stephan]

It is the fifth of the new month and so the average values of the "NOAA gases" are available.
Here is the value of CO₂:

April 2020:       416.21 ppm
April 2019:       413.33 ppm
Last updated: May 5, 2020

The annual increase is 2.89 ppm, a bit smaller than in April 2019 and much smaller than in April 2016, but higher than most of the other Aprils in my spreadsheet.

[Stephan]

I plotted the annual increases of Mauna Loa CO₂ from the monthly values from 1959 to 2020.
The best fit for the data is a linear one. Of course the data is noisy. Some years have seen a slow CO₂ increase, others (like 2016) had rapidly increasing values. In the long run there is a steady increase of the annual increase. Please keep in mind that this is an increase in slope, which means acceleration.
I do not see any sign for a hiatus or a turn around - I'd like to be able to report such an event...

See attached graph.

[wolfpack513]

NOAA's April Mauna Loa CO2 data was released: 416.21 ppm.  That's an increase of 2.88 ppm over April 2019.

April 2020's annual growth was higher than any of the previous 6 months & also higher than the running 12-month trailing average as well as the long-term linear average.

My next project is to detrend this dataset(subtract the linear regression from each month). Once detrended measure ENSO peaks to peaks & troughs to troughs trends: weak El Niño to weak El Niño, moderate La Niña to moderate La Niña and so forth for all strengths and flavors. I may even assign a lag of 2-4 months too account for the delay.

This should tease out acceleration better and see how much ENSO impacts these numbers. 

[dnem]

Tamino has done this sort of analysis, FYI:
https://tamino.wordpress.com/2018/01/20/is-co2-still-accelerating/

[Pmt111500]

Repeating the note I've made several times over the years. It's not surprising the CO2 keeps on rising in the spring, it is the high point of anthropogenic CO2  in the atmosphere. Once the plants have woken up from their hibernation they likely notice there's more of the stuff and adjust accordingly. Any anthropogenic decrease in CO2 production should thus be easiest to see in late summer-autumn numbers, once the natural cycle is changing it's direction.

[Stephan]

I do not agree with that statement as the annual increase rate strictly excludes seasonal aspects, assuming every growing season is comparable to earlier ones, which is not perfectly true, of course.
If there is a significant reduction in anthropogenic CO₂ emissions, it should be visible independent of the time of the year it happens. Of course the Mauna Loa CO₂ levels do not react on a day-to-day basis on such changes, a delay of the CoViD19-related reduction should be expected and is probably occurring very slightly and not abruptly.

[wolfpack513]

Repeating the note I've made several times over the years. It's not surprising the CO2 keeps on rising in the spring, it is the high point of anthropogenic CO2  in the atmosphere. Once the plants have woken up from their hibernation they likely notice there's more of the stuff and adjust accordingly. Any anthropogenic decrease in CO2 production should thus be easiest to see in late summer-autumn numbers, once the natural cycle is changing it's direction.

That's why I have a trailing 12-month average on my graph.  It smooths or removes the seasonal cycle.  Once you remove the seasonal cycle the rest of the variability is mostly ENSO.  The small changes from global economic ups and downs has an incredibly small impact of concentration time-series.  You can see dips on emissions charts but the impact is incredibly small on concentration time-series.  Something people confuse quite often.

[Stephan]

I also refer to my post # 93 from last week. I added to my weekly Sunday evening Mauna Loa posting a statement of NOAA concerning the answer to a FAQ concerning the consequences of the CoViD19-related lockdown on the global CO₂ levels.
It is worth a read.

[gerontocrat]

One must not forget that the increase in CO2 ppm also depends on the land and ocean sinks, which are in long-term decline due to amongst many other things,
- other human activities such as deforestation in the Amazon turning parts of the Amazon from net CO2 sinks into net CO2 emitters,
- winter CO2 emissions from the Permafrost regions (AGW x polar amplification),
- well-documented decline in the CO2 sinks in the Southern ocean,
- general reduction in ocean sinks as excessive CO2 being dissolved increases ocean acidity.

A one-year reduction in CO2 emissions is perhaps of not great significance - to consider it as more than a welcome blip is to grasp at straws?

[nanning]

- winter CO2 emissions from the Permafrost regions (AGW x polar amplification),

Dear gerontocrat,
Are you sure you don't mean summer CO₂ emissions from the permafrost regions? Perhaps I'm missing something.

[Phoenix]

A one-year reduction in CO2 emissions is perhaps of not great significance - to consider it as more than a welcome blip is to grasp at straws?

Agree 100%. The potential value of the Covid related decline is if people step back and realize how little it means in the big scheme of things and grasp that we need a more comprehensive approach.

[kassy]

The Covid signal can be discussed here so this thread can focus on Mauna Loa Co2 levels:
https://forum.arctic-sea-ice.net/index.php/topic,3078.0.html

[gerontocrat]

- winter CO2 emissions from the Permafrost regions (AGW x polar amplification),

Dear gerontocrat,
Are you sure you don't mean summer CO₂ emissions from the permafrost regions? Perhaps I'm missing something.

The permafrost regions are greening - i.e. absorbing more CO2.
A recent study showed that additional winter CO2 emissions outweighed the additional summer CO2 capture.

[Stephan]

It is Sunday evening and time for my weekly update of Mauns Loa CO₂ levels. But - there are no new weekly averages available tonight. I return to this point as soon as I can share the data with you.

[wolfpack513]

I de-trended NOAA's Mauna Loa C02 growth rates.  Included are Niño 3.4 monthly anomalies.  Niño indexes are already de-trended(3.4 uses a moving centered baseline). To smooth both I placed a 7-month trailing average.  I chose 7 months because the minimum criteria for La Niña or El Niño is 5 tri-monthlies(ONIs) or roughly 7 months.

Once you account for the 3-5 month lag of ENSO to CO2 concentration impacts, the residuals or variability in growth rates is nearly all ENSO.  I do need to adjust the quadratic used for de-trending Mauna Loa because the 2009-2010 moderate El Niño has the same amplitude as weak El Niños later in the time series.  A sign that acceleration in growth rates has picked up.

[Stephan]

Outlook:
The first week of May 2019 averaged at 414.3 ppm. I guess the actual peak will flatten out. We should expect an annual increase of 2.75 ± 0.25 ppm.

The latest weekly average of Mauna Loa CO₂ is available:

Week beginning on May 3, 2020:     416.83 ppm
Weekly value from 1 year ago:        414.11 ppm
Weekly value from 10 years ago:     392.98 ppm
Last updated: May 12, 2020

The annual increase is 2.72 ppm, almost exactly in the expected range. The 10 year average is lower (2.38 ppm) than this week's increase.
This week saw high intra-day, but low inter-day variations. It seems that we are close to the maximum. The highest daily average was probably reached on May 3^rd (418.1 ppm). It seens unlikely that the border of 420 ppm can be achieved this season. But 2021 will definitively go beyond that benchmark.

Outlook:
Last year next week was at 415.3 ppm, the maximum for 2019. I expect an annual increase of 2.0 ± 0.25 ppm, which would represent the highest weekly average for this year.

[Hefaistos]

...  I do need to adjust the quadratic used for de-trending Mauna Loa because the 2009-2010 moderate El Niño has the same amplitude as weak El Niños later in the time series.  A sign that acceleration in growth rates has picked up.

Thanks, wolfpack!

You say that the "acceleration in growth rates has picked up."
I don't see any such acceleration in the chart? To me, it looks like a deceleration, a slight negative trend in CO2 growth, ie. the blue curve.

[wolfpack513]

...  I do need to adjust the quadratic used for de-trending Mauna Loa because the 2009-2010 moderate El Niño has the same amplitude as weak El Niños later in the time series.  A sign that acceleration in growth rates has picked up.

Thanks, wolfpack!

You say that the "acceleration in growth rates has picked up."
I don't see any such acceleration in the chart? To me, it looks like a deceleration, a slight negative trend in CO2 growth, ie. the blue curve.

No, it’s de-trended.  Therefore the slope is flat.  However, the quadratic I used wasn’t perfect so the blue line could be adjusted some.  Any *short term* trend that you’re seeing is mostly ENSO. Of course after the super El Niño of 2015-2016 and nearly moderate El Niño of 2018-2019 your eyes see a negative trend.   Kind of my point.  Making any big declaration month to month or even year to year because growth rates went up or down is usually just ENSO.  Changes in emissions, including this year will be very small to detect but do have an impact in the longrun. 

[Pmt111500]

Detrending the anthropogenic signal out is of course a way to look for other (than ENSO) natural sources and sinks. Siberian 'relative' heat last winter might be an intersting phenomenon to study, was there a large outflux of CO2 and CH4 just as the winter set in? This could be in permafrost thread though.

[wolfpack513]

The internal variability is still mostly ENSO and that's the problem! We like to think that the 2008-2009 global financial crisis or corona-virus will make a big impact on *concentration* but it's tiny compared to where we need to be globally. Cumulative gas in the atmosphere doesn't care about your occasional emissions drop because the pie just keeps getting bigger. 

At the time it was a big deal when global emissions dropped ~0.50 GT from 2008 to 2009. That's a little less than a 2% drop in emissions.  Now compared that to ENSO which is responsible for plus or minus 2 ppm in growth rates variability: strong El Niño to strong La Niña.  You're working in different magnitudes.  Now if emissions were dropping 2% annually that would start to show up after some time.

[Pmt111500]

Fit a function to flatten the ENSO curve. Optimize the hell out of it, use what ever ENSO index flattens the bumps best... Try out adding a function for IOD. (This is where it gets really tricky) Stop as you do not anymore know what's signal and what is fitting the curve, or, this is how it happened to me a while back, I used the global weekly values of CO2 though. The slight variations round the globe flatten out some of the location-specific oddities. (In Mauns Loa I'd guess a derivation of an ENSO-index should be used as the hottest ocean waters pass the site not in sync with the general enso. This is Hard stuff, doctorate level some 20 years back, I'm pretty sure, maybe even nowadays on some subjects.

[wolfpack513]

Another thing that needs to be normalized or de-trended some is the fact that ENSO has been dis-proportionally warm phase the last 10 years.  The Niño index is already de-trended but depending on endpoints can influence the trend.  We all remember "no global warming since 1998."

[Pmt111500]

Another thing that needs to be normalized or de-trended some is the fact that ENSO has been dis-proportionally warm phase the last 10 years.  The Niño index is already de-trended but depending on endpoints can influence the trend.  We all remember "no global warming since 1998."

This is a real problem, we can't very well be sure what a stable climate El Nino looks like, so we can't easily say this change in El Nino is from Global Warming and this sort is regular behavior. Climate models give a clue, but a spontaneous development of an ENSO cycle is not easily achieved, I believe. But some models get those.

[Stephan]

Outlook:
Last year next week was at 415.3 ppm, the maximum for 2019. I expect an annual increase of 2.0 ± 0.25 ppm, which would represent the highest weekly average for this year.

The Sunday evening posting series on Mauna Loa CO₂ levels is back again.

Week beginning on May 10, 2020:     416.79 ppm
Weekly value from 1 year ago:          415.31 ppm
Weekly value from 10 years ago:       392.68 ppm
Last updated: May 17, 2020

The annual increase reduced markedly to just 1.48 ppm. The maximum for 2020 has passed, one week earlier than last year, which explains my "not so good" guess from last week. It is also much lower in comparison with the last ten years (average annual increase 2.41 ppm). This also makes it clear that the benchmark of 420 ppm has not been reached, not even in an hourly average.

Outlook:
Next week last year had an average of 414.8 ppm. Taking into account the actual downsloping curve I wouldn't be surprised if the annual increase goes even further down than this week.

[Stephan]

Outlook:
Next week last year had an average of 414.8 ppm. Taking into account the actual downsloping curve I wouldn't be surprised if the annual increase goes even further down than this week.

It is time for the weekly Mauna Loa CO₂ posting.
It comes as a surprise, but two weeks ago was not the weekly maximum, this week is slightly higher. We have a broad maximum this year. Therefore the annual increase has risen to 2.25 ppm, the ten year average increase is 2.35 ppm. The values:
Week beginning on May 17, 2020:     416.97 ppm
Weekly value from 1 year ago:          414.72 ppm
Weekly value from 10 years ago:      393.46 ppm
Last updated: May 24, 2020

Apart from yesterday ("unavailable") the whole week had constant CO₂ values with a very small intra-day variability.

Outlook:
Last year next week had an average of 414.2 ppm. When the plateau that has been reached now still holds on, then the annual increase can even move up a little further. It is impossible to say on which date finally the annual cycle with decreasing daily values will have its onset.

[grixm]

Perhaps the max has still not arrived. So far this week the average is not far from 418 ppm.

[Stephan]

...and May 25^th with 418.1 ppm, tied with May 3^rd, 2020, which was the highest daily average value ever measured so far. So we have two maxima this season?
Anyway, with the average of 414.2 ppm last year, we are heading towards an annual increase of above 2.5 ppm, unless a downward trend begins.

[Phoenix]

Perhaps the max has still not arrived. So far this week the average is not far from 418 ppm.

Looking back over recent years, it seems the CO2 numbers have tended to peak around May 15. The jump at this point in the calendar is concerning.

[Stephan]

I wouldn't put too much emphasis in this fact. The day-to-day variation is larger than the almost flat long-year trend mid to end May. But the downward trend should proceed from mid June on. Until then anything is possible, even a slightly higher value than on May 3 or 25.

[Phoenix]

I wouldn't put too much emphasis in this fact. The day-to-day variation is larger than the almost flat long-year trend mid to end May. But the downward trend should proceed from mid June on. Until then anything is possible, even a slightly higher value than on May 3 or 25.

Thanks. post 127 above refers to a weekly average which was a reason behind my interest. How many days did that represent?

[Stephan]

I think, grixm's post referred to my posting 126, in which I was surprised of the re-increase of CO₂ values the week before.
Posting 126 (as all other of my Sunday evening CO₂ postings) refer to the NOAA website, on which CO₂ average concentrations and its annual increase for the just passed week are published. So each individual annual increase I report contains the weekly values. Once a month (on the 5^th) NOAA publishes the monthly averages. I report this in an extra posting.
Link to NOAA: https://www.esrl.noaa.gov/gmd/ccgg/trends/index.html

[Stephan]

Outlook:
Last year next week had an average of 414.2 ppm. When the plateau that has been reached now still holds on, then the annual increase can even move up a little further. It is impossible to say on which date finally the annual cycle with decreasing daily values will have its onset.

Sunday evening, and it's time for an update of Mauna Loa CO₂ levels.
I guess the peak has now arrived. This should be the week with the highest average in 2020. The last two days saw a real decline with very little intra-day variations (that was not the case two weeks ago).
Week beginning on May 24, 2020:     417.43 ppm
Weekly value from 1 year ago:         414.40 ppm
Weekly value from 10 years ago:      392.63 ppm
Last updated: May 31, 2020
This results in an annual increase of just a little bit more than 3 ppm. The last 10 years' average increase is 2.48 ppm.

Outlook:
I bet that the annual cyclic downslope has started now. Last year next week saw an average of 414.3 ppm. So the annual average increase should be smaller, about 2.4 ppm.

[Phoenix]

Not sure where this belongs, but here's a link to a new study that makes the case that today's CO2 levels haven't been observed in 23 million years.

https://www.eurekalert.org/pub_releases/2020-06/gsoa-sst060120.php

The team used the fossilized remains of ancient plant tissues to produce a new record of atmospheric CO2 that spans 23 million years of uninterrupted Earth history. They have shown elsewhere that as plants grow, the relative amount of the two stable isotopes of carbon, carbon-12 and carbon-13 changes in response to the amount of CO2 in the atmosphere.

[wolfpack513]

I calculated 417.03 ppm for May 2020. This is roughly a growth rate of 2.4 ppm over May 2019.  Average done with a total of 26 daily NOAA readings. 

Once you de-trend Mauna Loa and offset for the 5-month ENSO lag, we're right where you would expect to be for growth rates.  May's growth rate reflects December 2019 ENSO conditions. 

I chose a trailing 7-month average to capture 5 ONIs(tri-monthlies).  2019-2020's weak El Niño for example: OND to FMA or October to April: 7 months.

[grixm]

We got a new daily record of 418.32 ppm for June 1st

[Pmt111500]

I calculated 417.03 ppm for May 2020. This is roughly a growth rate of 2.4 ppm over May 2019.  Average done with a total of 26 daily NOAA readings. 

Once you de-trend Mauna Loa and offset for the 5-month ENSO lag, we're right where you would expect to be for growth rates.  May's growth rate reflects December 2019 ENSO conditions. 

I chose a trailing 7-month average to capture 5 ONIs(tri-monthlies).  2019-2020's weak El Niño for example: OND to FMA or October to April: 7 months.

Enso corrected trend found, i think. You're obviously in this for a long haul. I'm not sure how to proceed from this. But looking good.

[Phoenix]

We got a new daily record of 418.32 ppm for June 1st

I understand that there is a lot of volatility in the daily result and no single day s/b cause for concern so someone shouldn't get concerned about this late season high in and of itself.

That said, what is the threshold at which people might become reasonably concerned about a longer "growing season" for CO2 ??

[Stephan]

The average value of Mauna Loa CO₂ for May 2020 is available.

May 2020:       417.07 ppm
May 2019:       414.65 ppm
Last updated: June 5, 2020

The annual increase is 2.42 ppm. This is roughly close to the average increase of the last 10 years.

I set the average of 1980 [338.75 ppm] as index=100. May 2020 is at 123.12 according to this index.

[rboyd]

Stephan,

This page provides the annual growth rates of atmospheric CO2 for Mauna Loa:
https://www.esrl.noaa.gov/gmd/ccgg/trends/gr.html

The average is 2.424, but this includes the large outliers of 2015 and 2016 due to the large El Nino of those years.

2010: 2.32; 2011: 1.92; 2012: 2.61; 2013: 2.01; 2014: 2.19; 2015: 2.99; 2016: 2.99;
2017: 1.89; 2018: 2.86; 2019: 2.46.

We dropped into a small La Nina configuration in May (shout out to Phoenix on the 2020 ENSO thread)
https://www.tropicaltidbits.com/analysis/ocean/
This may affect Mauna Loa more immediately than the global numbers given the Hawaii location.
So the current value is surprisingly high as La Ninas are associated with more oceanic CO2 and heat uptake than El Ninos.
The May numbers may also have some small negative effect from the global shutdowns that have reduced anthropogenic CO2 emissions.

The global number for March 2020 (reporting 2 months behind the Mauna Loa numbers) is 413.67 versus 410.61 a year previously - a 3.06ppm year over year rise. This is higher than any previous yearly average number, including the El Nino years. January was 2.63 and February was 3.13.
https://www.esrl.noaa.gov/gmd/ccgg/trends/global.html

[Stephan]

rboyd,
of course it is important to set the annual increases into context with [global] weather and current patterns. With definitively no El Niño in 2020 the increase rate is far too big to be acceptable. But it is above my pay grade to interprete the values. My intention was simply to present the actual numbers and compare the increase rates with those of the last decade(s).
I did so as well for the other "NOAA gases" (see the posts in the individual threads).

[Tom_Mazanec]

With definitively no El Niño in 2020 the increase rate is far too big to be acceptable.

So if we did have an El Nino in 2020 the increase rate would be acceptable?

[kassy]

Acceptable as in an expected outcome of conditions. He is clearly responding to:

So the current value is surprisingly high as La Ninas are associated with more oceanic CO2 and heat uptake than El Ninos.

[Stephan]

Outlook:
I bet that the annual cyclic downslope has started now. Last year next week saw an average of 414.3 ppm. So the annual increase should be smaller, about 2.4 ppm.

Sunday evening = update of Mauna Loa CO₂ levels.

This week saw the highest ever measured value (418.32 ppm see grixm's post this week). Since then the values were decreasing to what has been obeserved at the end of last week. This four days spike increased the weekly average.
Week beginning on May 31, 2020:     417.20 ppm
Weekly value from 1 year ago:          414.28 ppm
Weekly value from 10 years ago:      393.28 ppm
Last updated: June 7, 2020

The annual increase has therefore risen to 2.92 ppm, higher than expected and higher than the 10 year average increase (2.40 ppm). Nevertheless this week has not been the highest in this season (see my post from May 31).

Outlook:
Last year's next week had an average of about 414.1 ppm. With the latest values of this week the increase should reduce to about 2.4 ppm. The first half June is usually flat, the decrease to the annual minimum starts about the fourth week of June.

[wolfpack513]

A couple of things.  We mostly certain did have ENSO impacts through ~March.  You think of El Niño too much in a binary view: Niño 3.4(which did hit ONI criteria BTW).  2019-2020 warm water was displaced east of the warm pool creating an ocean-atmospheric teleconnection.  Clearly seen on VPs as well as increased global AAM.  Look at my chart above in the previous post.  detrended and lagged Mauna Loa fits perfectly with our low end El Niño.

You think that this is the first May where SSTs turned cold?  This happens in nearly every warm ENSO cycle.  slosh model: El Niños kill themselves because eventually an upwelling wave forms in response. These cooler waters won’t be seen for months in the CO2 data.  You guys often forget that Mauna Loa is used for a reason. At 11,000 ft it separated from the boundary layer atmosphere due to a nearly continuous strong marine inversion. Mauna Loa is measuring well mixed (globally)gases with little local impacts. 

rboyd,
of course it is important to set the annual increases into context with [global] weather and current patterns. With definitively no El Niño in 2020 the increase rate is far too big to be acceptable. But it is above my pay grade to interprete the values. My intention was simply to present the actual numbers and compare the increase rates with those of the last decade(s).
I did so as well for the other "NOAA gases" (see the posts in the individual threads).

[Stephan]

Outlook:
Last year's next week had an average of about 414.1 ppm. With the latest values of this week the increase should reduce to about 2.4 ppm. The first half June is usually flat, the decrease to the annual minimum starts about the fourth week of June.

Another Sunday evening - time for an update of Mauna Loa CO₂ concentrations.

Week beginning on June 7, 2020:     416.34 ppm
Weekly value from 1 year ago:         414.39 ppm
Weekly value from 10 years ago:     392.70 ppm
Last updated: June 14, 2020

The annual increase has significantly reduced (1.95 ppm) and is now again below the 10y average (2.36 ppm). From Wednesday on the intra- and inter-day variability is low. Before there was a huge fluctuation, one day was out of the quality gates of NOAA.
I also guess that there will be no further daily maximum this season. We are slowly in the downward trend.

Outlook:
Next week last year had an average value of 414.1 ppm. Extrapolating the actual trend into the next week I expect an annual increase of about 2.2 ppm.

[wolfpack513]

I made a mistake in my de-trending chart above.  I didn't de-trend ENSO before de-trending Mauna Loa. If you want to de-trend just *anthropogenic* effects you have to make sure ENSO(lagged) integrates to zero. 

I went with multi-line regression.  I have 4 regression lines where ENSO integrates to zero(accounting for 5 month lag). Blending these together you'll notice that anthropogenic changes are only worth about an additional ~0.1 ppm/year by 2020 compared to 2007. 

[Hefaistos]

I made a mistake in my de-trending chart above.  I didn't de-trend ENSO before de-trending Mauna Loa. If you want to de-trend just *anthropogenic* effects you have to make sure ENSO(lagged) integrates to zero. 

I went with multi-line regression.  I have 4 regression lines where ENSO integrates to zero(accounting for 5 month lag). Blending these together you'll notice that anthropogenic changes are only worth about an additional ~0.1 ppm/year by 2020 compared to 2007.

Thanks, Wolfie.
Two musings related to "anthropogenic changes are only worth about an additional ~0.1 ppm/year".

1. Clearly, we are not having exponential growth anymore, we're on a linear growth path.

2. What if ENSO has an anthropogenic component? Frequency, amplitudes, durations...

[Stephan]

1. Clearly, we are not having exponential growth anymore, we're on a linear growth path.

I do not agree. The rates are slightly increasing. The later you look the steeper is the slope.

I averaged 100-month increase rates of Mauna Loa CO₂:

1959-1967: + 0.77 ppm/year
1967-1975: + 1.10 ppm/year
1975-1984: + 1.50 ppm/year
1984-1992: + 1.52 ppm/year
1992-2000: + 1.59 ppm/year
2000-2009: + 1.99 ppm/year
2009-2017: + 2.34 ppm/year
2012-2020: + 2.48 ppm/year

These data are not compatible with "linear growth path".

See also the annual increase (raw data) in the attached graph. y-axis: increase in ppm/year