CO2 and the correlation with rising atmospheric temperatures

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I just read the policy for this forum "Earth" so i hope my next question will be approved, it is with the best intentions.
My friends and i where having a discussion about CO2 and the correlation with the raising temperature, we know that CO2 is a greenhouse gas. About that, CO2 is a greenhouse gas, there is to my knowledge no doubt about that. However is there consensus in the science community over how much influence the raising CO2 has on the temperature and if this is significant? I would understand if my question is to wide ranged. We were just curious!

Thanks in advance
P.S. sorry for my grammar mistakes
 
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.Scott

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I just reviewed the policy on this subject. It's close, but I don't think you've crossed the line ... yet.

Strictly speaking, it is not up to science to come up with a "consensus". Never-the-less, there is often great political practicality in doing so.
I would recommend taking a look at reports from the IPCC: https://www.ipcc.ch/

My own assessment is that the topic of climate change when viewed in terms of public policy is not as clear cut as it needs to be - but there is continuous progress.
Ideally, you would be able to predict both what would would happen if nothing was done and what would happen given a specific proposal - but that is not available. Still, policy decisions are commonly made with less than ideal information - which is necessary. Commonly you simply have to make an educated guess at whether the cost of a program will eventually be worth the expense.

So the real issue is whether science has provided good enough models to support significant (economy-changing) policy decisions. And I think there is still room for debate on that.

The last full assessment by the IPCC was done in 2014. That report is here: https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf
They are currently working on an updated version.
 
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Bandersnatch

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@.Scott the question wasn't about policy, but about the impact of CO2 on GW. I don't think there's any debate in the scientific community about its rising concentrations being the sole driver of the recent global temperature increase. My impression was the current work is focused on narrowing down climate sensitivity to further changes in atmospheric CO2.

@jochem I don't think this site is the best choice for making sense of this topic. We just don't have that many experts on the subject frequent these boards, and the forum policy is to some extent a reflection of that. You might get lucky, but more often than not you end up with a lot of essentially lay opinions.
 
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However is there consensus in the science community over how much influence the raising CO2 has on the temperature and if this is significant?
Hi,

This question is quite an old one. This subject started with Tyndall and Arrhenius in the 19th century. Guy Callendar will continue their work in 1930s and the theory that CO2 is a major driver of the average global temperature is becoming debated and popularized after WWII. Gilbert Plass in the 1950s published several papers that started to build the consensus around it:
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.2153-3490.1956.tb01206.x
https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.49708235307

Today, we have satellite data supporting that theory:
https://journals.ametsoc.org/doi/10.1175/2008BAMS2634.1

And direct measurement of the greenhouse effect in the atmosphere:
https://www.nature.com/articles/nature14240

If you are looking for an easy way to understand the concepts behind it and to have better arguments in your next debate, I suggest to go on the webpage of American Chemica Society:
https://www.acs.org/content/acs/en/climatescience/climatesciencenarratives.html

I hope it is what you are looking for.
 

.Scott

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Let's see if I can readdress the OP in light of the comments by @Bandersnatch.

It's somewhat difficult to address the notion of "consensus" because that's not part of the science of climate change.
I can find examples of the basis for a claimed "consensus" on the web - and the arguments are good - but they do not meet the criteria for citing articles on this subject in this forum.

But the key is "climate model" and it is discussed in that link I provided to "AR5".
https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf
That document is kind of the "top of the tree", with citations down to another level of IPCC documents, with citations to the actual science papers.
There are important terms on page 26 ("certainty", "likely", "very likely") that are used throughout the document to describe how well the assertions are supported by the research.

I am trying to be apolitical, but I think it is safe to say that there is a consensus among working climate models that the global warming that has been observed over the past three or four decades can be explained by rising CO2 levels alone and cannot be explained without considering those rising CO2 levels. I would not conclude from that that "rising concentrations [are] the sole driver of the recent global temperature increase". In fact, methane and N2O are certainly significant contributors (see figure 1.3 in AR5). I would conclude that rising CO2 is the primary contributor. I would also not discount agricultural water usage and contrails as potential noteworthy contributors.

Here is an article that describes the contrail issue. I am not citing it to support a claim that it is right - only that it is a "potential noteworthy contributor".
https://globalnews.ca/news/2934513/empty-skies-after-911-set-the-stage-for-an-unlikely-climate-change-experiment/

The OP also asked if these temperature changes are significant. This is a very policy-oriented question. Why else would you ask about the significance?
The AR5 document does describe projected consequences of global warming for the coming decades - and I think it does a passable job in defending those projections. But I think the reader needs to be very aware that there is a qualitative difference between a "very likely" estimate of historical trends based on collected data and a "very likely" projection based on a set of models - even though both are identified as "90-100%". Also, these are projections based on a modelling of all anthropogenic factors, not just CO2.

That said, you are more likely to find something that you consider "significant" in AR5 section 2 (projections) than in section 1. For example, the summary at the start of section 2 reads "Surface temperature is projected to rise over the 21st century under all assessed emission scenarios. It is very likely that heat waves will occur more often and last longer, and that extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level to rise.".
Section 2.3 gets into "impacts", for example:
Climate change over the 21st century is projected to reduce renewable surface water and groundwater resources in most dry subtropical regions (robust evidence, high agreement), intensifying competition for water among sectors (limited evidence, medium agreement). In presently dry regions, the frequency of droughts will likely increase by the end of the 21st century under RCP8.5 (medium confidence). In contrast, water resources are projected to increase at high latitudes (robust evidence, high agreement). The interaction of increased temperature; increased sediment, nutrient and pollutant loadings from heavy rainfall; increased concentrations of pollutants during droughts; and disruption of treatment facilities during floods will reduce raw water quality and pose risks to drinking water quality (medium evidence, high agreement).
 
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.Scott

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Am I the only one to find this article contradicting itself? Why it jumps on conclusion to choose specifically one side while the others statements suggest either the other side or the uncertainty.
As I said, I am not claiming that it is "right" - only that contrails should not be discounted. The gist of the article is that they can have an effect - potentially warming or cooling. It is part of my argument against the @Bandersnatch assertion that there is consensus that CO2 is the "sole" contributor.

I believe there were studies of the 9/11 climate effect. If anyone can find a good one, that would be great. I could not - but I don't have the scholastic resources that many others have on this forum.

That article does cite 5 other sources. The good ones are:
http://www.atmos.washington.edu/~rennert/etc/courses/pcc587/ref/Travis-etal2002_Nature.pdf (a NOAA article with good citations)
https://www.nasa.gov/home/hqnews/2004/apr/HQ_04140_clouds_climate.html

There are also indirect references (but no citations) to other articles more specific to the 9/11 effect.
 
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Bandersnatch

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I said the sole driver, of the current temperature rise.
 

.Scott

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I said the sole driver, of the current temperature rise.
If that's different from "sole contributor", then I don't think there are enough people with an opinion about it to constitute a "consensus".
But, I'll bite anyway: What is a "sole driver"?
 

russ_watters

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I just read the policy for this forum "Earth" so i hope my next question will be approved, it is with the best intentions.
Tone via "best intentions" matters a lot here. This thread opening is fine, and welcome to PF.
My friends and i where having a discussion about CO2 and the correlation with the raising temperature, we know that CO2 is a greenhouse gas. About that, CO2 is a greenhouse gas, there is to my knowledge no doubt about that. However is there consensus in the science community over how much influence the raising CO2 has on the temperature and if this is significant?
This isn't a complete and difinitive answer to your question, but a partial lab and consensus answer:
https://en.wikipedia.org/wiki/Global_warming_potential
https://www.epa.gov/ghgemissions/understanding-global-warming-potentials

Global Warming Potential is a quantitative/lab measurement/calculation of how much potential a certain gas has to affect global warming:
The GWP depends on the following factors:
The factors themselves are objective, but the weighting/scoring of these measurements can be debated. What isn't clear to me is how exactly the formula was arrived at, meaning to what extent the scoring represents a scientific consensus (by what scientists?) versus a political consensus.

[edit]
I realize on rereading I may have misinterpreted this post. When I saw "...how much influence the raising CO2 has..." I autocompleted "...vs other gases..." which may not have been intended. Maybe you intended vs other non-greenhouse gas factors such as solar output, random noise, etc. So maybe you'll find this informative, though maybe not quite relevant. I'll leave it be and let you decide if you want to pursue my angle.
 

russ_watters

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@.Scott the question wasn't about policy, but about the impact of CO2 on GW. I don't think there's any debate in the scientific community about its rising concentrations being the sole driver of the recent global temperature increase. My impression was the current work is focused on narrowing down climate sensitivity to further changes in atmospheric CO2.
I agree with your take on the OP, but the "sole driver" bit is way too strong. There are many climate drivers and more to the point, CO2 is not the only greenhouse gas humans are emitting large quantities of. In the media and politics, the issue is often simplified to be strictly about CO2, but it isn't. Off the top of my head and a quick google, human-caused methane release is 28% - more than a quarter - of the human caused global warming. This may not strictly be a required part of this thread, but in terms of policy it is critically important to decision making that by current measures, livestock methane (a part of that 28%) contributes more to global warming than all forms of transportation CO2 output combined.
https://www.skepticalscience.com/methane-and-global-warming.htm

This is the reason the GWP measure I referred to in my previous post exists.
@jochem I don't think this site is the best choice for making sense of this topic. We just don't have that many experts on the subject frequent these boards, and the forum policy is to some extent a reflection of that. You might get lucky, but more often than not you end up with a lot of essentially lay opinions.
This is true, but one thing we do have is quality standards that keep discussions on point and high quality. So while our best on this subject may not be as good as other subjects, it may still be better than other forums.
 
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russ_watters

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The OP also asked if these temperature changes are significant. This is a very policy-oriented question. Why else would you ask about the significance?
There are two potential uses of the word "significant" here. One is significant from a standpoint of whether it affects us enough that we should put effort into dealing with it. That's what you're referencing.

The other is "significant" from a statistical standpoint. E.G., is the 10 or 100 year change in average temperature larger - more "significant" - than the annual change? (10, no; 100, projected yes). Larger or faster than the millennial change? (faster, yes). The word is a bit of a value judgement, so (per a theme today...) we have to attach a scale to it to measure against. My read is this is what the OP was asking.

There is some overlap I suppose. One of the problems with acceptance has been the "significance" - the signal to noise ratio - of the data. When annual fluctuations are close to or larger than the long term measured trend, it is easy to speculate that the low signal to noise ratio makes the trend an anomaly. 10 or 20 years ago this may have been a valid concern -- or at least for a layperson like me tougher to pull the signal out of the noise than for an expert. Today, it's not.
 
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There are many climate drivers and more to the point, CO2 is not the only greenhouse gas humans are emitting large quantities of.
Not only that, but not all climate drivers are greenhouse gases. Another obvious one that humans have had a significant effect on is land use.
 

Bandersnatch

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@.Scott, et al
Reading it again in the morning, I agree it was a poorly worded statement that paints a picture that is too black and white. I don't want to be defending it too vigorously, and anyway it looks like we're all on the same page.
What I wanted to convey, is that while there are other contributors to climate change, they're either feedbacks (e.g. water vapour concentration, ice-related albedo changes), outright negative forcings (solar), or not comparable in magnitude to CO2 emissions (other greenhouse gases). Much like one could pin the driving influence to solar forcing at the end of glaciations, with other contributors acting as amplifying feedback.

But then again, that's still too black and white (aren't methane emissions comparable, really?).
 
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The gist of the article is that they can have an effect - potentially warming or cooling. It is part of my argument against the @Bandersnatch assertion that there is consensus that CO2 is the "sole" contributor.
I have no problem with the assertion that they have an effect. I am only surprised with the cherry-picking of the quote from Patrick Minnis where the entire sentence has been cut, resulting in a misleading assertion. Moreover, he didn't precise that the quote is incomplete and he add a baseline dot in the quote to suggest it is the entire sentence. It is something forbidden for us academicians. I find even more surprising to rely on an old study and an old news to talk about a complicated and currently debated subject. From a quality perspective, this news article from Patrick Cain is bad.

In 2018, there was a review in Nature on the effect of the contrails if you are interested:
https://www.nature.com/articles/s41467-018-04068-0

In 2005, a bit old but there was another review which is in open-access:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL022580
 

Astronuc

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Besides CO2, there are other gases that contribute to the warming of the atmosphere, e.g., methane. There does seem to be some different opinions on the relative importance of methane.

https://www.edf.org/climate/methane-other-important-greenhouse-gas
"About 25% of the manmade global warming we're experiencing is caused by methane emissions" and the site indicates that methane is 84 times more potent than CO2 in the first two decades after its release.

https://www.epa.gov/ghgemissions/overview-greenhouse-gases
A pie chart puts methane at 10% of emissions, but indicates "Pound for pound, the comparative impact of CH4 is more than 25 times greater than CO2 over a 100-year period."

So one needs to look at a variety of sources and understand how data are being presented.

As PeterDonis indicated, another factor is land use, e.g., deforestation (or more generally removal of plants) for buildings and agriculture. Building roofs and wall, roadways (asphalt and concrete) absorb light, heat up and emit in the infrared, as opposed to the trees or grass lands they replace. The EPA's site mentions "Carbon dioxide is removed from the atmosphere (or "sequestered") when it is absorbed by plants as part of the biological carbon cycle."
 

.Scott

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At this point in the discussion, I think it is becoming easier to see the boundary between science and climate policy.
Science has its customers - and policy-makers are near the top of the list.

If policy-makers are of a mind that they want to keep nature as it has been, then the models that have been created so far will suffice. They generally support the notion that we are changing weather patterns and "messing up" some fauna and flora and that we will be continuing to do so without policy change. In most cases, the studies do not meet the 3 or 5 sigma standard for accepted science, but that is not the criteria. You don't wait to jump out of the way of an oncoming train until you have a 5-sigma study demonstrating that it will hurt you.

On the other hand, those customers that have no interest in preserving the globe except as it impacts the industrialized nations will be less satisfied with the science - because it would be correctly viewed as incomplete. The models, as they are, suggest that there will be some negative impact outside of the tropics - but it clearly may be more cost effective (and economy-preserving) to brace for more storms rather than attempt to prevent them. More importantly, it isn't good enough to say that reducing CO2 emissions will mitigate the issues, they would want to know what portion of the problem belongs to CO2 because the rest of it will remain unaddressed with many CO2 reduction programs.
 
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If policy-makers are of a mind that they want to keep nature as it has been, then the models that have been created so far will suffice.
I'm not so sure that's actually true. I'm not sure that either the models or the evidence we have are sufficient to support specific policy interventions with good confidence that they will "keep nature as it has been", i.e., that they will reliably stop further change. I'm even less confident that we have enough predictive ability in economics to reliably say that, even if a particular policy intervention does mitigate what it's supposed to mitigate, that it will do so at a cost that is less than the benefit. Costs have a way of ending up being a lot more than they're predicted to be.

You don't wait to jump out of the way of an oncoming train until you have a 5-sigma study demonstrating that it will hurt you.
Agreed, but you also don't need a complicated argument based on models to tell you that jumping out of the way of the train will, with high confidence, prevent you from getting hurt.

those customers that have no interest in preserving the globe except as it impacts the industrialized nations will be less satisfied with the science - because it would be correctly viewed as incomplete.
I'm not sure that the current apparent fashion of describing this situation as a conflict between developed nations and developing nations is a good idea. As you note, in many cases it might be more cost-effective to adapt to the changes instead of trying to mitigate them; but it's much harder to convince developing nations to do that if they are told that their problems are the developed nations' fault. But that might be getting off topic since it's really a matter of politics, not science.
 
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I'm not so sure that's actually true. I'm not sure that either the models or the evidence we have are sufficient to support specific policy interventions with good confidence that they will "keep nature as it has been", i.e., that they will reliably stop further change. I'm even less confident that we have enough predictive ability in economics to reliably say that, even if a particular policy intervention does mitigate what it's supposed to mitigate, that it will do so at a cost that is less than the benefit. Costs have a way of ending up being a lot more than they're predicted to be.
You are comparing climate forecast with economical forecast? Everything related with human behavior is problematic because the causal link is difficult to prove and even difficult to measure. But climate science relies mostly on physics and chemistry. Contrary to most of the economical theories, the greenhouse effect and its role in the current warming do relie on empirical evidences and experiments. Climate forecasts are better and even the old model of James Hansen in the 80s made a good prediction matching the current measurements. If the American Chemical Society, the American Physical Society and The Geological Society of America support the consensus, there are good reasons for this. The same for the NASA, for the military and for insurances. Even Exxon and Shell in their own internal documents were in agreement with this. Moreover, the consensus is built since the 80s and since this time, we have increased the research on the subject by several orders of magnitude. And since this the consensus has been strengthen, not the opposite. No others explanation has been found with a sufficient criteria.

The only part where I agree with you is about the effect of a policy. Clearly, the human science part of our comprehension of the problem is the weakest. But for the physical and chemical parts, the most conclusive and significant theories grounded with the most solid evidences from climate science support the idea that reducing our emissions will reduce greatly the warming trend.
 

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