
Climate Models for Lawyers - VarFarYonder
https://judithcurry.com/2016/11/12/climate-models-for-lawyers/
======
snowwrestler
It is a common misconception that the theory of global warming, and the
concern about global warming, is based on the results of global climate models
(GCMs). It is not.

In fact, the _opposite_ is true: it is skepticism of global warming that
depends on the correctness of GCMs.

In the simplest model, which any kid can test in middle school, you take a
plexiglass box full of air (representing the atmosphere), add some extra CO2
to it, and see if the temperature goes up. It does.

Well, since the mid-1800s, we have been adding CO2 to the atmosphere. We know
that we've burned a lot of fossil fuels (that were underground), and we have
directly measured an increase in the amount of CO2 in the atmosphere. So based
on the simplest model, we'd expect to see the temperature going up. And we do!
Yay, science works.

Of course there are a lot of ways to say that the simple model is wrong. But
they all involve the construction of a more complex model. In order to see if
anything will mitigate or compensate the basic physics of how more CO2 traps
more heat, you have to add in additional factors.

So when someone goes on and on and on about the shortcomings of super-complex
GCMs, remember this. GCMs are important tools for making detailed predictions
and policy decisions, but we don't need them to predict the basic fact of
global warming.

In fact the original hypothesis of global warming dates back to about 1900,
well before anyone was using computers to model anything. The theory of global
warming rests on basic thermodynamics, and it was first proposed not long
after those basics were discovered.

~~~
serge2k
Is this how we ended up shifting from "global warming" to "climate change"?
Improved models showing that things won't just get warmer, they'll go all
kinds of sideways?

~~~
snowwrestler
The change in terminology doesn't have scientific significance, it was done to
try to improve public understanding.

Basically "warming" in popular usage means "I can take my jacket off now",
whereas warming in scientific usage means "increasing the heat energy stored
in a given volume."

Scientists have known for a long time that global warming (increasing the heat
stored in the atmosphere) would create both local heating in some areas and
local cooling in others (it's chaotic). But when a regular person hears
"warming" and then the temperature goes down, they're confused. Hence "climate
change."

Incidentally, predicting the local effects of warming is a major goal of GCMs,
and one for which no other tool will do. But it's damn hard (again: it's
chaotic).

------
spenrose
NASA climatologist Gavin Schmidt on Curry (Google cache):

My reading of the evidence suggests clearly that the IPCC conclusions are an
accurate assessment of the issue. I have tried to follow the proposed logic of
Judith’s points here, but unfortunately each one of these arguments is either
based on a misunderstanding, an unfamiliarity with what is actually being done
or is a red herring associated with shorter-term variability. If Judith is
interested in why her arguments are not convincing to others, perhaps this can
give her some clues.

[http://webcache.googleusercontent.com/search?q=cache:pLrHr9q...](http://webcache.googleusercontent.com/search?q=cache:pLrHr9q7_qkJ:www.realclimate.org/index.php/archives/2014/08/ipcc-
attribution-statements-redux-a-response-to-judith-
curry/+&cd=1&hl=en&ct=clnk&gl=us&client=safari)

~~~
barney54
This quote from Gavin Schmidt is two years old. I'm not sure what is has to do
with this blog post by Curry about what climate models are.

~~~
conistonwater
Note that this blog post is not "about what climate models are". It seems
she's been making the same types of arguments in the past, and this blog post
is no different, so the past criticisms are still relevant.

------
bcheung
"Scientists that evaluate climate models, develop physical process
parameterizations, and utilize climate model results are convinced (at least
to some degree) of the usefulness of climate models for their research. They
are convinced because of the model’s relation to theory and physical
understanding of the processes involved, consistency of the simulated
responses among different models and different model versions, and the ability
of the model and model components to simulate historical observations."

Anyone can create a model that behaves consistently when it is trained on
historical data to predict historical data.

How do they overcome the problem of overfitting and why should anyone have any
confidence in it until it shows accuracy going forward?

~~~
HCIdivision17
I think the key is in the last quoted sentence: there isn't one model. There
are many, and they are generated in different ways with differing emphasis on
different data sets. They gain confidence when these seem to agree with each
other and the acceptable physical knowledge already understood. They also
check the sanity of the model to make sure that it is consistent with what has
already been observed. In that way anyone may gain confidence that multiple
approaches are converging on similar results.

That, and there are metric crap-tonnes of data to work with of all sorts. Just
ungodly amounts of it.

------
scarmig
In other news:

[http://www.realclimate.org/index.php/archives/2016/11/record...](http://www.realclimate.org/index.php/archives/2016/11/record-
heat-despite-a-cold-sun/)

There was a lot of crowing about sunspots a couple years back by Judith Curry
et al. The Earth's heating can be explained by reaching a solar maximum! Etc.

But now the situation is reversed--the sun is cooling--and despite that we're
on track for yet another record year of heating. Third in a row.

Her points about model uncertainty and overfitting have some limited level of
validity. But it's hard to read her blog and not come away with the accurate
takeaway of she'll say whatever she can to provide a cover story for not doing
anything about AGW.

------
fencepost
Having skimmed the final paper and without being aware of Judith Curry or her
reputation, my initial reaction while reading was "This seems to be a white
paper in the school of 'here's something you can cite to justify why nothing
should be done about climate change/global warming/CO2 emissions/etc.'"

Looking her up afterwards, it seems to me that this may also be her push for a
significant position in the Trump administration. Seems that Judith Curry is
the scientist who says "Well, they've revised the likely range so clearly they
don't know what's likely and maybe it's too expensive to do anything right
now."

I won't bother linking, a simple search based on her name will turn up a wide
variety of links to her history, people bemoaning her stances, and people
refuting some of the arguments she uses.

~~~
mdisc
Yeah it's kind of sad actually. I started reading this as serious piece and
then sent it to a professor I had during my undergrad for a class on climate
change. So embarrassing!!

The broad points about training data and non-linearities are important- but on
a second pass it's hard to believe that people who spend their lives building
GCMs don't think deeply about these challenges.

~~~
jamez1
I think the worrying thing is that it's not hard to believe, she's pointing
out the breakdown of the scientific process.

She cops a lot of flack and hysteria, just for raising reasonable doubts!

If climate science is solid, then it shouldn't feel the need to vilify anyone
who questions it. If it isn't solid then it should be subject to as much
scrutiny as possible given the derived policy will have tremendous impacts to
life.

------
nkurz
Could someone with domain knowledge give feedback on the specifics she brings
up? As I take it, the backbone of her argument is:

1) "If climate sensitivity is high, then we can expect substantial warming in
the coming century as emissions continue to increase. If climate sensitivity
is low, then future warming will be substantially lower."

2) "In fact, it seems that uncertainty about values of ECS has been
increasing. The bottom of the ‘likely’ range has been lowered from 2 to 1.5oC
in the AR5, whereas the AR4 stated that ECS is very unlikely to be less than
1.5oC. It is also significant that the AR5 does not cite a best estimate,
whereas the AR4 cites a best estimate of 3oC. The stated reason for not citing
a best estimate in the AR5 is the substantial discrepancy between observation-
based estimates of ECS (lower), versus estimates from climate models (higher).

3) "If the climate sensitivity is on the low end of the range of estimates,
and natural internal variability is on the strong side of the distribution of
climate models, different conclusions are drawn about the relative importance
of human causes to the 20th century warming."

4) "Whether or not human caused global warming is dangerous or not depends
critically on whether the ECS value is closer to 1.5oC or 4.5oC."

5) "Given the uncertainties in equilibrium climate sensitivity and the
magnitude and phasing of natural internal variability on decadal to century
timescales, combined with the failure of climate models to explain the early
20th century warming and the mid-century cooling, I conclude that the climate
models are not fit for the purpose of identifying with high confidence the
proportional amount of natural versus human causes to the 20th century
warming."

Is this an accurate summary of facts? Do we have good evidence about the true
value of ECS that she does not mention? Is there evidence for scenarios where
a 'low end' Equilibrium Climate Sensitivity still results in a dangerous
warming? Or are there indeed values for ECS that would be considered 'likely'
but do not result in dangerous warming?

Lack of knowledge about the true value of ECS is not an excuse to avoid
precautionary measures, but it would seem to raise questions about the
suitability of current climate models as predictors for future climate. At the
least, it would imply that determining the true ECS should be a very high
priority while other mitigation measures are taken.

~~~
xapata
It sounds like she's advocating for a political policy of doing nothing,
because of "uncertainty". Consider our position on risk/uncertainty when it
comes to minor disasters like an airplane hijacking. Now consider the
appropriate response to the risk of a nation-destroying disaster. Is it
reasonable to take the do-nothing policy?

~~~
nkurz
While there is probably a legitimate fear that others will use her evidence to
claim that , I see her as making a more limited claim in this piece: current
GCM's cannot reliably be used to make definitive claims about climate a
century out, and therefore should not be relied on for policy decisions unless
their true uncertainty (model risk) is accounted for. Which quotes from this
piece do you read as a "call to inaction"?

That said, it's true that she does write elsewhere about her belief that
uncertainty does not necessarily increase the urgency of action:
[https://judithcurry.com/2016/01/05/climate-models-and-
precau...](https://judithcurry.com/2016/01/05/climate-models-and-
precautionary-measures/). I haven't read many of the linked posts, but it
would seem fair to summarize her position as something like "we don't yet have
sufficient understanding of the problem to justify taking actions that will
cause definite harm".

~~~
xapata
If "definite harm" includes moderate financial cost, that's a disastrous
policy.

------
jwatte
"I conclude that the climate models are not fit for the purpose"

Without any statistical treatment at all. And then later puts "expert opinion"
of others in quotes.

At that point, I lost confidence in the analysis. Do some well known numerical
and statistical tests of the models, and create a Bayesian based estimate
based on all the models, and see where you end up instead!

~~~
jamez1
Perhaps you missed her point about selection bias? Only models confirming
climate change can be published, any analysis is just going to confirm that.

It's unfortunate because climate change could be happening, but we aren't
going to learn much more about it because research can't be invalidated. We've
killed the skepticism science needs to function.

She's not denying it's happening, she's just not buying the grandiose
narrative. I'm glad to hear her view, even just to know that it's there.

------
mdisc
Ah, yes she is a bit of a skeptic-
[http://www.skepticalscience.com/Judith_Curry_arg.htm](http://www.skepticalscience.com/Judith_Curry_arg.htm)

~~~
mdisc
One point that it looks like Curry takes aim with more generally is the degree
to which there is a consensus about global warming among scientists. She says
that 97% of scientists can't believe in it because they haven't studied it or
built their own models, etc -- they have "second order belief"

That's an important epistemological point to make. I guess we should all make
our own GCMs to confirm for ourselves that we believe in AGW?? Sure maybe if
we all had unlimited time. In science we share a common set of methodological
beliefs and assumptions-- maybe there's a breakdown for her there, but I'd
like to think the at the research institutions and tools that exist help
accurately propagate true findings to the public especially in a matter that's
as pressing to our long term wellbeing as climate change!

~~~
basurihn
Research institutions did a pretty poor job of telling us cholesterol
consumption causes atherosclerosis. Largely because we discounted minority
scientific opinion.

