3 ms·

Whenever I see this figure reported on a numerically literate site like HN, I always wonder how many readers know whether the thermal forcing due to CO2 is (a)

by kapitza 10y ago

Whenever I see this figure reported on a numerically literate site like HN, I always wonder how many readers know whether the thermal forcing due to CO2 is (a) exponential, (b) logarithmic, or (c) linear as a function of the ppm. Upvote if you didn't know the answer and had to Google it? Downvote if everybody knows the answer and it's a stupid question?

cornchips 10y ago
(b) logarithmic Good question to pose.
- SamPhillips 10y ago
  Yes, but is the rate of growth of CO2 concentration sublinear, linear or superlinear?
deleted 10y ago
[deleted]
gizmo686 10y ago
I had just assumed it was logarithmic due to my high school understanding of the greenhouse effect. To save people googling, it appears that I was right [0], however this is not try for all greenhouse gasses. For instance, methan grows as sqrt(x), and CFCs are linear. Admittedly, the linked expressions are empirical, so only represent an approximation for the range of values that we have observed. There are also dynamic effects (such as increased water vapor, or a runaway release of trapped methane) that are not being moddeled by estimates of thermal forcing. [0] http://www.esrl.noaa.gov/gmd/aggi/aggi.html http://www.esrl.noaa.gov/gmd/aggi/aggi.html
- kapitza 10y ago
  The thermal forcing is just the input to the model. What we'd really like to know is the climate sensitivity -- how does a given forcing affect Earth's temperature? All questions about the legitimacy of climate science are questions about whether simulations of the earth's atmosphere ("general circulation models") can be validated or have predictive power, at least with realistic computing resources. However, the big-O question is an interesting reflection on the ratio between how much scientific communication effort goes into influencing the public, versus educating the public. There is also not much funding available for studying positive impacts of global warming. Scientists have known about the Arrhenius effect for over a century, and in pre-WWII texts the treatment is generally "isn't it cool that burning fossil fuels not only gives us power and light, but is good for agriculture and might prevent the next ice age?" The past is a foreign country, and in that country it was generally assumed that warm periods were good for humans and cold ones were bad. (Mostly because ag yields.) They didn't even really think about it -- and nor do we think much about it, either. Plus ca change...
mSparks 10y ago
Aside from the fact it's a good question. I'm also upvoting because that "sounds" like maybe you are pessimistic about the significance and need them to recoup the robo downvotes given to anyone not willing to swear the worlds going to end tomorrow. (don't know for sure if they lurk on HN, but for sure they are everywhere else).
tim333 10y ago
Not exactly any of the above although it can be approximated by (b). See http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/ http://www.realclimate.org/index.php/archives/2007/06/a-satu... for some details
credit_guy 10y ago
In addition to that please raise your hand if you know why the answer to the above question is irrelevant for understanding climate change. Choose the best answer: A) CO2 is by far not the most important greenhouse gas B) the climate change is driven by complex interactions among (mainly) CO2, water vapors, clouds, precipitations, sea surface evaporation, air currents C) the thermal forcing mentioned above is determined assuming none of the interactions in point B) D) all of the above
- s_kilk 10y ago
  I’ll bite: D?
- MagnumOpus 10y ago
  By elimination, only (B) is true. (A) is false - while water vapour has high radiative forcing, it is not "an important greenhouse gas" in the big picture, unlike what the coal industry reps say. This [1] should explain why. Methane and CFCs are far less important in aggregate (about 1/3 and 1/4 of the effect of CO2 respectively), although they are far more dangerous per unit of volume. (C) is obviously false - even in the low level layman explanation in [1] you can see that they include a table with the forcings of various combinations (like H2O vapour+CO2); you can also see that the table is from 1978, so scientists have done that since way before you were born. (D) false [1] http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/ http://www.realclimate.org/index.php/archives/2005/04/water-...
  - credit_guy 10y ago
    Thanks for your thoughtful reply and your link. I think that article is quite informative, and also well written. I guess it was not authored by the coal industry, but still it states literally "water vapor is indeed the most important greenhouse gas".

by kapitza 10y ago

cornchips 10y ago

(b) logarithmic Good question to pose.

SamPhillips 10y ago
Yes, but is the rate of growth of CO2 concentration sublinear, linear or superlinear?

deleted 10y ago

[deleted]

gizmo686 10y ago

I had just assumed it was logarithmic due to my high school understanding of the greenhouse effect. To save people googling, it appears that I was right [0], however this is not try for all greenhouse gasses. For instance, methan grows as sqrt(x), and CFCs are linear. Admittedly, the linked expressions are empirical, so only represent an approximation for the range of values that we have observed. There are also dynamic effects (such as increased water vapor, or a runaway release of trapped methane) that are not being moddeled by estimates of thermal forcing. [0] http://www.esrl.noaa.gov/gmd/aggi/aggi.html http://www.esrl.noaa.gov/gmd/aggi/aggi.html

kapitza 10y ago
The thermal forcing is just the input to the model. What we'd really like to know is the climate sensitivity -- how does a given forcing affect Earth's temperature? All questions about the legitimacy of climate science are questions about whether simulations of the earth's atmosphere ("general circulation models") can be validated or have predictive power, at least with realistic computing resources. However, the big-O question is an interesting reflection on the ratio between how much scientific communication effort goes into influencing the public, versus educating the public. There is also not much funding available for studying positive impacts of global warming. Scientists have known about the Arrhenius effect for over a century, and in pre-WWII texts the treatment is generally "isn't it cool that burning fossil fuels not only gives us power and light, but is good for agriculture and might prevent the next ice age?" The past is a foreign country, and in that country it was generally assumed that warm periods were good for humans and cold ones were bad. (Mostly because ag yields.) They didn't even really think about it -- and nor do we think much about it, either. Plus ca change...

mSparks 10y ago

Aside from the fact it's a good question. I'm also upvoting because that "sounds" like maybe you are pessimistic about the significance and need them to recoup the robo downvotes given to anyone not willing to swear the worlds going to end tomorrow. (don't know for sure if they lurk on HN, but for sure they are everywhere else).

tim333 10y ago

Not exactly any of the above although it can be approximated by (b). See http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/ http://www.realclimate.org/index.php/archives/2007/06/a-satu... for some details

credit_guy 10y ago

In addition to that please raise your hand if you know why the answer to the above question is irrelevant for understanding climate change. Choose the best answer: A) CO2 is by far not the most important greenhouse gas B) the climate change is driven by complex interactions among (mainly) CO2, water vapors, clouds, precipitations, sea surface evaporation, air currents C) the thermal forcing mentioned above is determined assuming none of the interactions in point B) D) all of the above

s_kilk 10y ago
I’ll bite: D?
MagnumOpus 10y ago
By elimination, only (B) is true. (A) is false - while water vapour has high radiative forcing, it is not "an important greenhouse gas" in the big picture, unlike what the coal industry reps say. This [1] should explain why. Methane and CFCs are far less important in aggregate (about 1/3 and 1/4 of the effect of CO2 respectively), although they are far more dangerous per unit of volume. (C) is obviously false - even in the low level layman explanation in [1] you can see that they include a table with the forcings of various combinations (like H2O vapour+CO2); you can also see that the table is from 1978, so scientists have done that since way before you were born. (D) false [1] http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/ http://www.realclimate.org/index.php/archives/2005/04/water-...
- credit_guy 10y ago
  Thanks for your thoughtful reply and your link. I think that article is quite informative, and also well written. I guess it was not authored by the coal industry, but still it states literally "water vapor is indeed the most important greenhouse gas".