Allowable 'carbon budget' most likely overestimated

Credit: CC0 Public Domain

While most climate scientists, including the Intergovernmental Panel on Climate Change, implicitly define "pre-industrial" to be in the late 1800's, a true non-industrially influenced baseline is probably further in the past, according to an international team of researchers who are concerned because it affects the available carbon budget for meeting the 2 degrees Celsius (3.6 degrees Fahrenheit) warming limit agreed to in the Paris Conference of 2015.

"The IPCC research community uses a definition of preindustrial that is likely underestimating the warming that has already taken place," said Michael Mann, distinguished professor of atmospheric science and director, Earth System Science Center, Penn State. "That means we have less to burn than we previously thought, if we are to avert the most dangerous changes in ."

The researchers explored a variety of date ranges for defining a "pre-industrial" baseline and the likelihood that, compared to those baselines, the averages could be held to 2 C (3.6 degrees F) or to the preferred 1.5 degrees C (2.7 degrees F). They report their results today (July 24) in Nature Climate Change.

"When the IPCC says that we've warmed 1 degree C (1.8 degrees F) relative to pre-industrial, that's probably incorrect," said Mann. "It's likely as much as 1.2 degrees C (2.16 degrees F)."

Because greenhouse gas concentrations have been increasing since 1750 it would be preferable to define a baseline prior to then, but actual instrumental measurements of did not exist before the 1800s. There are also natural phenomena that preclude defining a single unique value for pre-industrial average global temperature.

"What period do you choose?" said study lead author Andrew Schurer, research associate in the School of Geosciences, University of Edinburgh. "Temperatures change due to natural factors such as volcanoes and fluctuations in the sun. If we choose the period 1600 to 1700 we get a different baseline temperature, for example, than if we choose 1500 to 1600."

The researchers estimated the temperature baseline using simulations from the Coupled Model Intercomparison Project Phase 5, the current suite of models used for research. They used a mixture of simulated sea-surface temperatures and surface-air temperatures to mimic actual global temperature observations. They also used three different scenarios for future carbon emissions that assume varying levels of aggressiveness in combating climate change.

They found that assuming the traditional late 19th-century baseline and using the highest future emissions scenario, by the middle of this century, the temperature rise will likely be about 4 degrees C (7.2 degrees F). With a moderate emissions scenario, the researchers found that keeping below 2 degrees C was still unlikely. Only the most aggressive scenario for reducing carbon emissions is likely to keep the temperature rise to 2 degrees C or less.

The researchers then considered all possible century-long periods for defining a baseline from 1401 to 1800 and used 23 simulations with seven different models. They found that anywhere from 0.02 to 0.21 degrees C (0.036 to 0.378 degrees F) warming took place prior to the late 19th-century period conventionally used as a baseline. Depending on which interval is chosen, the baseline could differ by almost nothing to a fifth of a degree C.

"A widely used metric for climate change mitigation is how much carbon we can still burn and remain below 2 degrees C," said Mann. "It's what we call the 'carbon budget.'"

A pre-industrial baseline that truly contained no human-caused warming would alter the amount of carbon that could be put into the atmosphere. Measured in gigatons of carbon, to account for the 0.2 degrees C likely unaccounted for in previous estimates of human-caused warming, we would need to burn 40 percent less carbon to remain below the 2 degree C threshold, according to Mann.

"Either the Paris targets have to be revised," said Mann. "Or, alternatively, we decide that the existing targets really were meant to describe only the warming since the late 19th century."

If nothing else, Mann says that the community needs to be far more precise in defining what baselines are being used in setting targets.

Explore further

UN climate panel to explore 1.5-degree warming goal

More information: Importance of the pre-industrial baseline for likelihood of exceeding Paris goals, Nature Climate Change (2017).
Journal information: Nature Climate Change

Citation: Allowable 'carbon budget' most likely overestimated (2017, July 24) retrieved 20 September 2019 from
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Jul 24, 2017
"A pre-industrial baseline that truly contained no human-caused warming" That would be what? About 50 thousand years ago before humans discovered how to make fire? Or possibly longer? We can reduce co2 as much as possible but it's not going to make a whole lot of difference at this point. We were already in a warming cycle and we have just speeded it up a bit. It's not going to get cooler until the cycle goes back in the other direction again. Then people will be trying to figure out how to stop an ice age. We will have a totally green with plant life Antarctica first though and this time Greenland will really deserve the name....

Jul 24, 2017
Michael Mann the hockey stick man. He's been caught is so many lies it baffles me anyone listens to him.

Jul 24, 2017
Just remember those of you with Carbon Fetish, all the carbon in the crust and most of what is in the mantle, was once CO2 in the air, that, and only 500 million years ago, more or less*. None of the petroleum, coal or limestone is older than 500 million years because it took photosynthesizing and exoskeleton building micro-organisms to fix the carbon.

*hint the world didn't die or turn to Venus.

Jul 25, 2017
We can reduce co2 as much as possible but it's not going to make a whole lot of difference at this point.
A very dismissive comment. How much are we willing to bet on such arm chair science? This article gives a good perspective on the time frames involved. https://earthobse...age3.php Look at the second graph - showing the past 1,500 years. The data is clear - we are causing warming that is significantly faster than the natural variation. There are now 7 billion of us living here. The biosphere is going to adapt to this accelerated warming. If we can stop the accelerated warming - and buy ourselves time to study the whole situation - it would seem prudent to me. Especially if we can find win/win/win solutions such as renewable energy. Accelerated warming could be great - and lead to a much more livable world. Or it could screw us with a great extinction event. Any one for craps?

Jul 25, 2017
Instead of focusing on the temperature, what about looking at the atmospheric carbon isotope ratio (C12/C13) and compare that to the past natural carbon cycle. The earth has been fine for millions of years without us burning fossil fuels. Obviously there were events that were outside of anything humans could prevent with current technology (Ice Ages, Catastrophic Volcano Eruptions, Meteor Strikes, etc.),but the planet recovered and now here we are burning shit freely.
Outside of major events,the C12/C13 ratio has been fairly stable and within what the natural carbon cycle could handle. The ratio started to decrease dramatically around 1750,or the start of the Industrial Revolution. True,we didn't have instrumental temperature measurements before 1800,so we have to use the Hydrogen and Oxygen isotopes found in ice,or other proxies,to infer a temperature for that time frame. I would think that the C-ratio would be a better number to focus on and then use the associated T, so pre-1750.

Jul 25, 2017
No it wasn't a very dismissive comment. We are on a warming cycle. It's been going on since the last ice age. It's going to continue until the the planet cycles around back to an ice age again. We have speeded up the process. You will either figure out a way to survive or not. Many people in the world will not. That's reality. You people can click on the 1's all you want. It's not going to change the reality of what is happening.

Jul 25, 2017
We have speeded up the process. You will either figure out a way to survive or not. Many people in the world will not
whereas this is absolutely true, there is no reason to concede defeat in the first move of the game, either

you don't quit playing chess after the first two moves, right?
nor do you quit playing the first time another player takes a piece of yours (or do you?)

this is still early in the game

we obviously have the ability to alter the climate because we did exactly that with our massive dumping of CO2 and other GHG's into the atmosphere

worse still, we did it without realising or testing the potential side effects (like the relationship between CO2 and WV)

so if we can cause the problem, why can't we fix or at least mitigate the damage?

Jul 25, 2017
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Jul 25, 2017
No it wasn't a very dismissive comment. We are on a warming cycle. It's been going on since the last ice age. It's going to continue until the the planet cycles around back to an ice age again. We have speeded up the process. You will either figure out a way to survive or not. Many people in the world will not. That's reality. You people can click on the 1's all you want. It's not going to change the reality of what is happening.

It IS a dismissive comment, written from a position of high arrogance, if not ignorance.

Jul 25, 2017
You will either figure out a way to survive or not
Please elaborate. Do you mean that as an individual I will figure out a way to survive? I think we are all in this together - and the most important point is our collective response, not my individual response. Earning over $100,000 per year - it is very easy for me to jump in the nice pool I recently put up in the back yard when temps soar over 100 degrees - as they are currently doing in the mid west. A/C in the house nicely set to 80 degrees - and no real problem for me if the unit goes out - and have to shell out $10,000 for a new one. Not so easy for the poor people of Inidia - https://thinkprog...951335de In your world view - do I have no responsibility - at least in terms of my attitude - for the poor people I have just linked you to? I live on 1/2 acre, and grow more than enough food to feed the two of us. cont.

Jul 25, 2017
cont. That is provided there is enough rain, or the city water holds out. Of course - if the shit really hits the fan - bad dudes with guns are probably going to take my tomatoes away from me - and not sure what I will do when I get appendicitis, or some other serious ailment. I guess you can pull out your own teeth with pliers if you have to. Don't you think it is better if we listen to the scientists - and try to figure out a collective response - that will keep us all alive? That does not only apply to global warming, but ebola, safe drinking water, cancer treatment, etc. etc.

Jul 25, 2017
I didn't say we weren't going to try to do all we can to slow it down. I just said it is happening whether we like it or not. A lot of people are going to have to move north or south from the equator and a lot of them are not going to survive. Sure we will try to help like building water purification systems, power systems and probably all kinds of other ways but it's going to happen. I'm not conceding defeat at all. I'm a realist. I don't particularly care if people disagree with me. They have their view of the situation happening and I have mine. If people want to consider that arrogance will I guess that's their privilege. It won't change reality though.

Jul 25, 2017
If people want to consider that arrogance will I guess that's their privilege. It won't change reality though.
Well 2 issues here. Firstly - clearly reality can be changed. We are changing it right now - by loading the atmosphere with GHG, and accelerating the earth's warming. You have conceded this. So surely there is no harm in at least trying to back off on the amount of GHG we produce - especially if we can find win/win/win like renewables. Secondly - you don't answer the question about our responsibility to others on the planet. You very casually acknowledge that 'a lot of them are not going to survive.' Is that it? Fuck em - I am doing fine - so no big deal if a lot of them don't survive? Do you not see that this attitude may lead people to think your being arrogant?

Jul 25, 2017
I have no problem at all backing off the pollution we produce. I think we need to go to green energy as fast as we can but that's also going to take decades and a lot of infrastructure improvements. I think you are misunderstanding what I meant. I said WE -- meaning people of the planet- will be trying to help as much as we can when it happens. Or at least some countries will try to help. It is going to be a disaster. Of course I don't want people to die - where did you get that idea. I didn't say that. I just said people are going to die and the reason is because they won't all be able to move fast or easily enough. Half of them or more will probably be fighting over what resources are left to them. That seems to be the first response for a lot of people when a problem occurs.

Jul 25, 2017
Well 24volts - seems to me that you are very contradictory. First you say
. It's not going to change the reality of what is happening
and then you say
we need to go to green energy as fast as we can
Do you see the contradiction? Either there is no point in trying to respond (as your first statement implies) - or there is. I take the latter position.
Other point - yes we are in a warming trend - caused primarily by Milankovich cycles - but the problem science is looking at currently - is - as you concede - that we have accelerated that trend. This may be very problematic in terms of the biospheres adjustment. Rather than be a fatalist - and say there is nothing we can do about it - why not be a part of the solution - and let the scientists inform us of what is going on - and guide policy in terms of the best path forward?

Jul 25, 2017
If you go back to the article and read the title it is pretty frightening what we are facing. We are currently at 408ppm of CO2 according to With continual FOSSIL fuel combustion you can easily imagine that doubling to 800ppm or more which is certainly at extinction levels. (You just turned us into a cool Venus cenario). Anything we do that increases CO2 levels now is just pile-on to where we currently are in global warming, and once that level is achieved it takes 1000s of years to get back to the global temperature environment your parents lived in.

So if I was in the EPA, I would be declaring an ALL-HANDS-ON-DECK-EMERGENCY!!!

Jul 26, 2017
Greenonions I originally had you blocked because of your trolling people. You obviously can't seem to read simple english without making up your own words. I fell sorry for anyone that has to deal with you on any constant basic because you are the type of person that if someone told you the sky was blue you would argue for 2 days over what shade. Your going back to being blocked. I'm not wasting any of my time trying to explain something simple to you since you insist on 'misunderstanding' everything .

Jul 26, 2017
I'm not conceding defeat at all. I'm a realist
not sure i agree with this, especially because of this end statement
It won't change reality though
now, you may well be a realist regarding most human behaviour, but you seem to specifically disregard technology and it's considerable advancement of late

one thing that a realist will also consider is this: it's a world threat

it is entirely possible that as things degrade and become worse, the world will literally move to work as a unified species to address the problem, unlike what it is doing today for various reasons, be it idiocy like the denier movement or lack of education or religious idiocy & similar problems


i also think that greenO has brought up some valid points regarding your behaviour, so you should consider them

at times you advocate the electric looneyverse bullsh*t even though you're not eu, but then at other times you are lucid

personal history is important
it speaks to intent

Jul 26, 2017
since you insist on 'misunderstanding' everything .
24volts - notice that on this thread alone - 3 people (me, Zzzzz, and Captain Stumpy) have taken issue with your comments. Perhaps you could wonder if it is your communication style that is causing the problem, and not my 'misunderstanding.' There is a famous line often used in communication class - 'What you think I just said - may not be what I meant you to hear' - or something along those lines. Here is the statement you made that I take issue with
We can reduce co2 as much as possible but it's not going to make a whole lot of difference at this point
That to me is a very dismissive comment. It is counter to the science. We have accelerated the warming by injecting GHG into the atmosphere. You conceded that. But you offer no explanation for why it may not work in the opposite direction. When responding to deniers - we often deal with arguments that are weak, and thrown up over and over. cont.

Jul 26, 2017
cont. One of those often used arguments is that the earth goes through warming and cooing cycles - this is just part of the natural cycle of things - nothing to see here - move along. We encounter this crap over and over. We counter it - as I did by showing the graphs that I linked to. And then the argie bargie begins. So great - put me on ignore. I will continue to respond when I see what I read as trite, dismissive, hackneyed arguments - which may just be a difference in communication styles between you and me - but I will continue to be able to make my point.

Jul 26, 2017
24 volts - let me try one more approach. In your comments - you concede that the climate is warming, we have accelerated that warming with GHG's, that warming is going to cause the displacement of populations around the world - and as a result of said displacements - people will die. Is that an accurate read of your comments?
Question (that I already asked - and you refrained from answering) - do you acknowledge any responsibility to other travelers on this planet - in terms of the problems they are going to face - as a result of this situation?
Would it not at least be a start - to acknowledge the science behind AGW, and to consider - at the very least - attitudinal changes - that would show compassion to those who are going to be displaced - and to at least start thinking about/discussing - appropriate societal changes?

Sep 20, 2017
Looking back towards 1600 we get closer and closer to the little ice age. In other words they are conflating warming that is recovery from the ice age with human caused effects. It is almost certainly the case that this warming would have happened anyway. In fact, using an AI machine learning algorithm a team recently was able to feed temperature data into the algorithm and then ask the AI to predict temperature since 1880. The AI predicted better than the 23 billion dollar computer models the temperature without needing CO2 anywhere in the data the variations in temperature since 1880. How? How could it do that?

Because the AMO/PDO cycle and 1000 year cycle of the LIA and MWP, Roman warm period going all the way back to the holocene optimem actually predict that temperatures would peak in 2000 and there is a 60 year cycle layered on top. Viola no CO2 and the exact graph. Makes you think.

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