CO2 – Why 450 ppm is Dangerous and 350 ppm is Safe

dangers of elevated CO2

In my October 29, 2013, blog, Stranded Assets or Stranded Humanity. Choose One, I reviewed the math that supports leaving 80% of known fossil fuel reserves in the ground. That would allow us to limit the concentration of CO2 in the atmosphere to 450 ppm (parts per million) and have a 50:50 chance of limiting global warming to 2°C. Now scientists are telling us that this is a very dangerous and irresponsible strategy.

In September 2013, the Intergovernmental Panel on Climate Change (IPCC), the international body for assessing the science related to climate change, released its fifth assessment report. Authored by 250 climate scientists from 39 countries, it states: “It is extremely likely that human influence has been the dominant cause of observed warming since the mid-20th century.”The IPCC report goes on to describe the cumulative effect of our carbon dioxide (CO2) emissions.

“Emissions of CO2 from fossil fuel use and from the effects of land use change on plant and soil carbon are the primary sources of increased atmospheric CO2. Since 1750, it is estimated that about 2/3rds of anthropogenic [human] CO2 emissions have come from fossil fuel burning and about 1/3rd from land use change. About 45% of this CO2 has remained in the atmosphere, while about 30% has been taken up by the oceans and the remainder has been taken up by the terrestrial biosphere. About half of a CO2 pulse [emission] to the atmosphere is removed over a time scale of 30 years; a further 30% is removed within a few centuries; and the remaining 20% will typically stay in the atmosphere for many thousands of years.”

How urgent is the climate change issue? The urgency depends on how soon we will exceed what scientists deem to be a safe level of carbon dioxide in the atmosphere. Four levels of carbon dioxide concentrations in the atmosphere frame our choice.

  1. 280 ppm (Pre-indiustrial): The pre-industrial concentration of CO2 in the atmosphere in the 1750-1850 timeframe was about 280 ppm (parts per million).
  2. 400 ppm (Today): Between the start of the industrial revolution and May 2013, human activity increased the concentration of CO2 in the atmosphere to 400 ppm. These elevated carbon dioxide concentrations have already increased the average global temperature above pre-industrial levels by 0.85°C. As a result, we are experiencing severe weather events with wild extremes in temperature and precipitation. Climate scientists describe these anomalies as early signs of climate destabilization. Even if we stopped increasing CO2 levels now, the temperature would still rise other 0.8°C above the 0.85°C that we’ve already warmed, because of the cumulative effects described by the IPCC, above.
  3. 450 ppm (High risk):The OECD Environmental Outlook to 2050: Key Findings on Climate Change” summarizes predictions by climate scientists’ models: we have a 50% chance of stabilizing the average global temperature at a 2°C increase over the pre-industrial period if we keep concentrations of CO2 under 450 ppm. A November 2013 report by PwC, Busting the carbon Budget, says that at our current rate of fossil fuel usage in the global economy, we will exceed that limit by 2034.
  4. 350 ppm (Safe):  Many leading climate scientists do not have that appetite for risk. A December 2013 report by James Hansen, Johan Rockström, and 15 other scientists, “Assessing ‘Dangerous Climate Change’: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature,” declares that 2°C of global warming would have disastrous consequences and could cause major dislocations for civilization. (The bold highlighting is mine.)“Cumulative emissions of ~1000 gigatonnes of carbon (GtC), sometimes associated with 2°C global warming, would spur “slow” feedbacks and eventual warming of 3–4°C with disastrous consequences. …  Rapid emissions reduction is required to restore Earth’s energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice.

    “Witting”? If it were “unwitting,” it would be accidental. “Witting” means it would be deliberate and that we are fully aware of the dire consequences of our actions. It would be a march of folly.The authors advocate for a target of 350 ppm as the maximum safe concentration of CO2 concentration, which would stabilize the global temperature at 1°C above pre-industrial levels and avoid runaway climate destabilization.

That 350 ppm / 1°C limit gets my vote. But is it possible to reduce CO2 concentration to the 350 ppm level, given that concentration is already at 400 ppm? Yes. See my November 12, 2013, blog, A 12-Step Program for Our Fossil Fuel Dependency, for how.

The only thing missing is political leadership to make it happen. How long will we tolerate that witting abdication of responsibility? When threatened by terrorist bombings, countries declared a War on Terror. When threatened by rampant drug addiction, countries declared a War on Drugs. Climate change is biggest threat ever faced by humanity. Isn’t it time we declared a War on Climate Destabilization?

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29 replies
  1. William Lopez
    William Lopez says:

    I’m a middle school teacher, and I make it a point to inform my students about the effects of CO2 in the atmosphere. I show them the current level of CO2 in the atmosphere (403.7 ppm) which is displayed on, and explain to them how carbon absorbs heat energy from the sun. It’s fascinating to hear my students express concern about climate change. Teachers more than anyone else are on the front lines of fighting this battle. We must educate the next generation to ensure that they will not continue making the same mistakes that their predecessors made. Unfortunately, I speak with my adult friends about this topic, and they seem indifferent and unconcerned just like the politicians they vote for.

  2. karla
    karla says:

    nearly 2 1/2 years have passed since you wrote this, ending on that rather optimistic note. we are now at 407 ppm and 1.48 over 1910 temps. 1.99 if you look at the land mass of the Northern Hemisphere. for the last 12 months we have smashed heat records every month. there appears to be sign this will stop.

    no new technology has materialized to replace the consumption of fossil fuels. to advance that solar and wind are still saviors is folly. they require mining, manufacturing, transport, installation and maintenance. things that all require more environmental devastation and use of fossil fuels.

    technology, civilization, over population and capitalism, the system that demands constant growth to survive are root causes. there is not enough time to shut things down, to stop the planet from hitting 2C much, much earlier than anyone thought. (well, than we thought, i’m sure the powerful saw this coming. that’s why they are just letting the infrastructure rot and focusing on becoming more violent abroad).

    so, what is your updated time frame for collapse? or do you still deny its a possibility?

  3. Bob Willard
    Bob Willard says:

    Karla, I share your concern about the lack of progress. However, I do not agree that we can’t mitigate the situation. We have the technology. We have the evidence that a green economy provides more and better jobs. Renewable technology is affordable. What is missing the will to make the transition. If / when we decide to do it, we can do it … but we are running out of runway to take off on this exciting journey.

  4. Keith Henson
    Keith Henson says:

    Started soon and pushed hard, I know of one project which could end the use of fossil fuels short of 440 ppm and bring the level down as much as is wanted. It would lower the cost of energy at the same time.

    Shorter version that was shown a the White House in April as a result of the D3 awards

    The videos are about power satellites as a solution for CO2

    For more detail on the graphs, the slides for a two hours talk to the engineers at Reaction Engines are here:

  5. arnie borr
    arnie borr says:

    I am 68 and remember from grade school & high school talking about about all the coal & oil we were using and when we would run out and how this could effect our climate. In the 60’s we became concerned about these problems but our political and capitalist leaders chose to continue on with profits & business as usual. I believe our leaders are mainly still in this mindset. We must elect persons who will attack this problem. We don’t have the right to hand this off to our grandchildren.

  6. Bob Willard
    Bob Willard says:

    I agree, Arnie. I’m older than you and have three young grandsons. They are my inspiration to do what I can to avoid climate destabilization. This is personal. Bob

  7. Keith Henson
    Keith Henson says:

    “our political and capitalist leaders”

    The problem is that the leaders don’t have a clue as to how to solve the problem in a way that leaves their skins intact.

    They understand that coming down on fossil fuels hard enough to make a difference will run up the cost of energy and put the economy into a depression. That’s what happened in 1974. With a depression going the current leaders will be tossed out and the new ones will back off reducing the CO2.

    What they need is a way to generate cheap renewable energy in vast amounts. And they have forgotten who to ask, namely engineers. I have been working on this problem off an on for over 40 years, and in the last year we seen to have found a new way to accomplish an old scheme, power satellites. It has not been verified and is less than a year old now. If you want to see how it works, there are a couple of videos linked off

  8. Bob Willard
    Bob Willard says:

    Keith, I agree that space-based solar power (SBSP) has great untapped potential and that it is hard not to get into conspiracy theories on the reasons why it has not been exploited. Go for it! Bob

  9. Drew Sallans
    Drew Sallans says:

    Hello, I am 15 years old. I saw the updates on Co2’s atmospheric ppm online only a few days ago and have been researching any chance I get. What I have found startles me. Not only the information and how it will affect my life, but the lack of caring done by both older and younger generations. What we need to realize is that people that do not care don’t understand this crisis, or have given up hope to stop it. What needs to be done is people need to inform the public more on this issue and maybe people will start doing something. However, the way I see it we only have 12ish years to make drastic changes before it’s to late. I ask you, please try to make a difference if you can, please try to restore hope in others, and please encourage others to make changes in their lives. If nothing is done, I and my children will grow up in the aftermath of one of the worst cataclysms the world has ever faced. ( I don’t want to sound desperate but this situation is scary. If temperatures get raised over 2°C then we could see oceans become more acidic, desalination occure, not to mention the destabilization of the jet stream that lies in the wake of desalinized oceans. In addition we are looking at a looming water crisis due too fracking, unsustainable farming practices, and overpopulation. These issues need to be addressed or people will die and we will take much of earth biodiversity with us.)

  10. Bob Willard
    Bob Willard says:

    I agree, Drew. I have grandsons your age. They are the reason I do what I do. This is personal. We have the technology to do what needs to be done. we have the resources to do what needs to be done. What is missing in the WILL to do it. Thanks for helping to awaken people about how close we are to the tipping point. Bob

  11. Bob Willard
    Bob Willard says:

    Richard, I used to teach earth science many, many years ago. I agree that is sets a wonderful context for how humans need to treat our spaceship Earth. The Future-Fit Business Benchmark uses best-available science to define the necessary level of company performance on 21 environmental and social issues. We need to pay more attention to scientific principles that define the way in which we treat each other and our finite planet. Bob

  12. Keith Henson
    Keith Henson says:

    I know of a couple of engineering projects that could make a difference.

    One of them is at The other is described in a couple of videos at

    The first looks like it could provide base load power for around 5 cents per kWh. The second looks like 3 cents per kWh or less.

    More if anyone is interested, or you can join the power satellite economics google group.

  13. karla
    karla says:

    i sincerely doubt there is 15 years left to reel in this problem. we’ve already hit too many tipping points and set off too many feedback loops. all these ‘green’ ideas about solar and wind and other solutions fail to factor in we would still need to mine and produce, ship and install and then maintain and replace ALL of that stuff. and you can’t do that without fossil fuels and further degradation/depletion of resources.

    meanwhile, the world keeps breeding and oil is cheap. people are lining up to go on “see it while it’s still here” tours along with making plans for both oil exploration and tourism in the arctic. mankind is INSANE. and not in a fun, cool way. that we waited this long to even begin to set up a binding agreement between nations (and just as corporations are pushing to see TTIP/TTP implemented which will completely BLOW those binding agreements apart).

    i am sorry for the younger folks left holding the bag. you are inheriting a dismal mess. and there is really nothing that can be done. the severe effects of climate change we are seeing right now are but the results of the CO2 added 30 to 40 years ago. shutting the switch off and returning to the stone age right NOW will not see any immediate reduction or roll back in the violence of the storms and wonky weather we’ve got ahead of us.

    so hug your loved ones and prepare for war. cuz it’s going to get much uglier.

  14. Laszlo Baranyai
    Laszlo Baranyai says:

    Being an Electrical Power Engineer and Climate Researcher we face this problem everday. And I hate to say it that there is no easy solution. Over the years we have developed alternative technologies to help combat the issue but it is no easy task. You can’t simply eliminate 1 thing and achieve another and not have consequences or repercussions. Yes the burning of Fossil based fuels has greatly contributed to the problem but isn’t the only problem. Greenhouse gasses aren’t only limited to CO2 but other ozone depleting ones as well. When we use technology to combat the problem there inherent risks that go along with it. In truth, reducing the carbon footprint as an individual has by farther greater effects than government imposed ones. Businesses need to play a greater role be responsible as well. Recycle, Reduce, Reuse. I could write a 100 pages on the pros and cons of virtually all the alternatives available. But that is outside the scope of this discussion. My suggestion is this. Make the most responsible choice you can on everything you do. Be it walk, bike, use your car, whether you recycle or not, compost or not, wash your clothes in cold water etc. Remember that everything you do impacts the environment in some way. Good or bad.

  15. Tim mcHugh
    Tim mcHugh says:

    Well, I want to start by saying that I believe it’s in our best interest to be cautious about our use of resources and the corollating impact on the environment. But I feel I have to address a few issues that come to mind with points mentioned in this essay. First of all the climate of this wonderful planet has been anything but stable for the past 2 million years. Statistically the normal climate of the past two million years has been much colder to the point of being referred to as the ice age. Technically we are In a brief warm period between glaciations or an interstadial. The Holocene period in which we now live is only the latest in a series of brief interstadials between much longer periods of heavy glaciation where average global temps are up to 10 degrees Celsius or 18 degrees Fahrenheit colder with ice sheets thousands of feet thick covering much of the continental northern hemisphere. The Holocene period itself has been characterized by an unstable climate with periods both warmer and colder than the current climate. The most recent extinction level event occurred at the beginning of the Holocene and was most likely not caused by human activity. The couple degree temperature increase is completely within the normal fluctuations which have been occurring all throughout the Holocene and minuscule in comparison with the changes associated with shift from glaciation to interstadial periods and vice versa. I do not doubt one bit that human industrialization is contributing to the recent warm up, but the idea of a stable state of homeostasis within the climate is a complete misrepresentation of the scientific data. I am personally more concerned with toxins being dumped into the environment than the increase of CO2. My point is there is no normal climate to try to stabilize to. We don’t really understand the reasons for the naturally occurring ups and downs that are well documented.
    What I have a real problem with is relating the environmental problems we are facing and the potential solutions to wars on drugs and terror. These have been two of the most hypocritical, politically motivated, hyped up, and self defeating endeavors that our country has been fooled into funneling resources into. I dare say they have been dangerous distractions which have been very divisive to our own country and the human race in general.
    I’m all for protecting the environment and getting away from fossil fuels and the associated green house gases and toxic emissions, but we really need to be honest about what we do and don’t know and focus on problems we know how to solve like not dumping industrial waste in to our water ways and reducing the introduction of toxins, pesticides, heavy metals into the environment.

  16. Bob Willard
    Bob Willard says:

    Tim, we disagree about the root causes of climate destabilization, but we agree that there are other pressing environmental (and social) problems to address. There is no lack of urgent opportunities for innovative solutions. Bob

  17. IDNeon
    IDNeon says:

    Well this article is already blown-away. And to people who say “we must educate the next generation” … you’re kidding yourselves. There won’t be any need to educate the next generation because before they have any political power at all the world will irreversibly cross 450ppm.


    Regardless what the hopeful charlatans tell you once CO2 is in the atmosphere it’s there to stay, unless you can find a REAL carbon sink and not merely some oceanic trade-off.

    There is NO SUCH real Carbon Sink on Earth today.

    As I write this, decades ahead of schedule, the Earth has irreversibly crossed the 410ppm CO2. 450 is almost here, probably another 10-20 years.

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Trackbacks & Pingbacks

  1. […] Power was born in 1995 when the level had reached 360 ppm, above the 350 ppm that some scientists consider a safe level. (That level was exceeded in […]

  2. […] is today, July 3 2014, 400.44 parts per million; dangerously close to the 450 ppm level that climate scientists have warned us we must not approach, let alone cross. At current rates of CO2 dumping into our atmosphere, we will reach 450 ppm in twenty […]

  3. […] three-to-five year range used throughout the business case simulator. However, as pointed out in my January 7 blog, extreme and weird weather associated with climate destabilization is already happening. If we […]

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