The IPCC and the term most

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In summary, the IPCC does not have a specific definition for the term "most" in their Fourth Assessment Report. The reason for this is likely to allow for legal wiggle room. However, based on data from the report, it can be estimated that humans have caused approximately 93% of the observed increase in global average temperatures since 1750. The IPCC may have used the term "very likely most" as a way to avoid having to define "most" and "predominate," which could have led to even more ambiguity. Ultimately, the definition of "most" can vary and is open to interpretation.
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BCO
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The IPCC and the term "most"

An online "sparring partner" brought up an interesting point during one of our regular (some would say never-ending) climate debates the other day. He asked me for clarity on what the IPCC means by "most" in their Fourth Assessment Report when they say:

"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations."

The reports are quite clear in defining quite specific definitions for "very likely," "likely" etc. but there seems to be no attempt at all to quantify the term "most". Does "most" mean 51% or does it mean closer to 90%? Or is it somewhere in between? Maybe most is 71.2% - who knows? Does it matter? Obviously there's a lot of "wiggle room" in this definition, unless it's clarified somewhere in another IPCC document and I have just not looked in the right places.

Any assistance on this would be great. Thanks,

BCO
 
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  • #2


It doesn't have a specific meaning it's just a summary, it's there for the usual legal wiggle reasons.
if they said "All the observed increase in global average temperatures since the mid-20th century ...' then some country could come along and say:
- But the temperature rise in one area of Hawaii is due to a volcano erupting, therefore the report contains a false statement, therefore it's all wrong and we can all get new bigger SUVs
 
  • #3


Since 1750 anthropogenic warming has resulted in
a net positive forcing of +1.6 [+0.6 to +2.4] W m–2.

Over the same time, solar changes have contributed +0.12 [0.06 to 0.3] W m-2.

[1.6]/[1.6+.12] => 93%

So, since 1750, humans have most likely caused about 93% of the warming.

Most of the solar increases occurred prior to 1950 or so and
solar activity is currently very low. So, the amount of
warming from human causes since 1950 maybe greater
than 100%. In other words, there may have been
global cooling since the 1950's without human intervention.
 
  • #4


Would it be possible to pevent an ice age in the future by deliberately pumping large amounts of CO2 in the atmosphere, or would that not work?
 
  • #5


Thanks for the answers, both.
 
  • #6


Count Iblis said:
Would it be possible to pevent an ice age in the future by deliberately pumping large amounts of CO2 in the atmosphere, or would that not work?


Yes; that is essentially what we are doing.

Ruddiman has a paper showing that we humans have actually
been doing that with CH4 and CO2 for several thousand years.

http://earth.geology.yale.edu/~avf5/teaching/Files_pdf/Ruddiman2003.pdf [Broken]

Not everyone agrees with him, but I suspect he is mostly correct.
 
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  • #7


Xnn said:
...
So, since 1750, humans have most likely caused about 93% of the warming...

This doesn't explain why the IPCC failed to quantify the term "most" in the same manner that they did for "likely" and "very likely" etc.

Would you say that "most" means >90% ?
 
  • #8


seycyrus said:
This doesn't explain why the IPCC failed to quantify the term "most" in the same manner that they did for "likely" and "very likely" etc.

Would you say that "most" means >90% ?

Not to mention it implies the only two possible causes of warming are solar and man made.
 
  • #9


It's a quote from a press release of an executive summary.
You could have the entire report totally correct if it was entirely written in lambda calculus but its message might be a little more difficult to follow.
 
  • #10


seycyrus said:
This doesn't explain why the IPCC failed to quantify the term "most" in the same manner that they did for "likely" and "very likely" etc.

Would you say that "most" means >90% ?

No; Generally "most" is considered to mean >50%.

Notice the IPCC has defined "very likely" as >90% probability.

Since more than 93% of the warming is manmade, perhaps
the IPCC decided it fair to use the "very likely most" term.

However, it probably could have been equivalently worded:

"Likely the predominate amount of warming since the mid 20th century is man-made."

However, in that case they'd have to define what "most" and "predominate" meant
and they decided it was easier to define the other set of words instead.
 
  • #11


"Most" means whatever I would like it to mean. It could be anywhere from 0-100%. Most people agree with this definition.
 

1. What is the IPCC?

The IPCC stands for the Intergovernmental Panel on Climate Change. It is a scientific body established by the United Nations in 1988 to provide policymakers with regular assessments of the scientific basis of climate change, its impacts, and future risks, as well as options for adaptation and mitigation.

2. What is the role of the IPCC?

The role of the IPCC is to assess and synthesize the latest scientific research on climate change, and communicate this information to policymakers and the public. The IPCC does not conduct its own research, but rather reviews and evaluates existing studies to provide a comprehensive and unbiased assessment of the state of knowledge on climate change.

3. What does the term "most" mean in the context of the IPCC?

In the context of the IPCC, the term "most" is often used to refer to the majority or central tendency of scientific findings. This means that the conclusions and statements made by the IPCC are based on the most widely accepted and robust scientific evidence, rather than individual studies or outliers.

4. How does the IPCC gather and review information?

The IPCC relies on the expertise of hundreds of scientists from around the world who volunteer their time to contribute to the assessment reports. These scientists are selected based on their knowledge and expertise in the relevant fields of climate science. The IPCC also conducts a thorough review process, including multiple rounds of peer review and government review, to ensure the accuracy and objectivity of the information presented in its reports.

5. How does the IPCC support decision-making on climate change?

The IPCC's assessments and reports are used by governments and policymakers to inform their decisions and actions related to climate change. These reports provide a comprehensive and objective overview of the current state of knowledge on climate change, including its impacts and potential solutions. The IPCC also provides guidance and recommendations for adaptation and mitigation strategies based on the best available scientific evidence.

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