Another post on climate change...
Oh Lord! Here we go! Bells are going off in your head. I can hear it.
You've already made up your mind on what this is about. Your opinion is made. The conversation is now off of the rails with no hope of resuscitation. End of discussion. Your done...
Please, allow me to finish.
A few months ago after reading some climate articles posted on Twitter, I tracked down the author--a well known climate scientist--on Facebook. I had read many of this individuals posts before and wanted to ask the scientist a few follow up questions.
Before I show our question and answer exchange, Remember several things about me. 1) I hate politics. 2) I love science and weather and 3) I strive to better understand the cognitive biases that govern my thinking. In a nutshell, no politics here; all science (I do have my own personal scientific views on this subject). Yet my goal of this exercise is to present the science as objectively as possible with compelling scientific arguments filtered through a lens that washes out my own potential cognitive biases so as to promote a civilized scientific discussion. A tall order for anyone to do. Humility is tough to chew.
In an attempt to diminish any preconceived notions you might have. the scientist's identity will stay concealed. I will refer to this scientist as "Pat". Laugh if you must.
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Question 1:
When we look at the length of the droughts of the 1930s, they were much longer and more severe according to the PDSI (Palmer Drought Severity Index) data. Once again playing devils advocate, why is this year's drought different?
Hi Scott--as I understand it, we set all time records for the % of the country (>60%) in drought this past month. By several metrics, this summer's drought exceeded what has been seen for any other single year. The issue of persistence of drought (i.e. how many years in a row a given state is in drought) is something else, that takes several years to evaluate. While the drought of the 1930s already likely had an anthropogenic component (soils were warmer, and evaporation was greater, than it would have been prior to anthropogenic warming), this year's drought likely had a much greater anthropogenic component, as many regions broke all-time temperatures that were set in the Dust Bowl years.
Question 2:
Is there a way to determine whether or not the NAO (North Atlantic Oscillation), AO (Arctic Oscillation), ENSO (El Nino or La Nina), etc plays more of a part in a specific weather episode (extreme warmth, etc) than AGW? Can the models do this considering that the NAO, for example, is more random in its behavior than say ENSO? Doesn't the PDO and AMO have impacts as well or are they mitigated due to the AGW (Anthropogenic Global Warming) signature?
Is there a way to determine whether or not the NAO (North Atlantic Oscillation), AO (Arctic Oscillation), ENSO (El Nino or La Nina), etc plays more of a part in a specific weather episode (extreme warmth, etc) than AGW? Can the models do this considering that the NAO, for example, is more random in its behavior than say ENSO? Doesn't the PDO and AMO have impacts as well or are they mitigated due to the AGW (Anthropogenic Global Warming) signature?
Well the problem is that anthropogenic climate change may have a projection onto each of these modes, so the separation isn't clean. However, this is where the science gets considerably more uncertain, not the least of which because signal-to-noise ratios are quite a bit lower (the internal variability noise is very large). However, its probably fair to consider the distribution of weather regimes as basically stationary. i.e. we had large positive AO/NAO excursions, etc. in the past, and there is nothing clearly extraordinary about the atmospheric circulation patterns we are seeing, the only thing that appears extraordinary is both the scale and magnitude of the warmth. But I don't don't that we'll see a fair bit of attention paid to these questions over the next few months and climate scientists perform a scientific 'autopsy' on the anomalous 2012 North American summer warmth...
Question 2B:
Thank you so much. Would it be a safe assumption to say that the +++AO/NAO last winter was more a random fluctation? Is the behavior of the AO linked to arctic ice lose/gain?
Scott--that is a great question, to which I wish I knew the answer. There are theoretical arguments that have been made for a tendency for both a more positive AO/NAO and a more negative AO/NAO. The sea ice impacts are more speculative and
not currently well represented in the models, and so its hard to put too much confidence in the model projections w.r.t. this issue. But the absence of evidence is not the evidence of absence, and if I were a betting man, I would suspect that sea ice melt did play a role in the anomalous AO/NAO state last winter and *could* be a harbinger of what is to come...
Question 2B:
Thank you so much. Would it be a safe assumption to say that the +++AO/NAO last winter was more a random fluctation? Is the behavior of the AO linked to arctic ice lose/gain?
Scott--that is a great question, to which I wish I knew the answer. There are theoretical arguments that have been made for a tendency for both a more positive AO/NAO and a more negative AO/NAO. The sea ice impacts are more speculative and
not currently well represented in the models, and so its hard to put too much confidence in the model projections w.r.t. this issue. But the absence of evidence is not the evidence of absence, and if I were a betting man, I would suspect that sea ice melt did play a role in the anomalous AO/NAO state last winter and *could* be a harbinger of what is to come...
Question 3:
One other question (there is always another :) Doesn't the negative PDO and the warm pool in the central Pacific drive the western trough and thus the continental ridge creating an upper level environment that is more conducive for sustained heat/Texas drought in 2011? I believe you addresses this last week in another response but is the AGW signal embedded within the overall upper level pattern? Finally, does an increase in CO2 in the oceans alter the PDO, AMO cycles. Is seems as if they are fairly consistent...Sorry, that was 3 questions :) Thanks, Scott
Scott-no question the anomalous atmospheric circulation, which in part is set up by large-scale SST patterns ("PDO" is a bit of a pet peeve--itis just an imperfect characterization of changing North Pacific SST patterns that contain both anthropogenic and natural variability contributions) has something to do with the North American drought. But without dispute, the drought has been worsened by record-breaking heat, that leads to greater loss of moisture from soil via evaporation and evapotranspiration.
Scott-no question the anomalous atmospheric circulation, which in part is set up by large-scale SST patterns ("PDO" is a bit of a pet peeve--itis just an imperfect characterization of changing North Pacific SST patterns that contain both anthropogenic and natural variability contributions) has something to do with the North American drought. But without dispute, the drought has been worsened by record-breaking heat, that leads to greater loss of moisture from soil via evaporation and evapotranspiration.
Question 4:
Concerning the AMO, I have read some draw a causal relationship between the +AMO (Atlantic Multidecadal Oscillation) and arctic ice cap growth/melting. Could the +AMO cause or enhance the rate of melting? Thanks Scott
Concerning the AMO, I have read some draw a causal relationship between the +AMO (Atlantic Multidecadal Oscillation) and arctic ice cap growth/melting. Could the +AMO cause or enhance the rate of melting? Thanks Scott
Hey Scott. In the study discussed by Appell in the link, the AMO (a coin I actually termed--as I discuss in my book) is estimated as being responsible for at most 30% of observed melt. My guess is that its less than that--30% is just an upper-bound estimate.
Question 5:
In order for AGW to directly cause the heat waves like current one in the US, would the increase in temp need to be caused by an increasingly stronger continental ridge cause by a change in the wave pattern around the globe? In other words, is AGW causing the wave pattern to change? Is this a correct supposition?
Scott--fair question. But no, you can't explain the record-breaking warmth by atmospheric circulation alone. We've had very similar circulation anomalies in mid-summer in the past, and they didn't lead to the same level of warmth. So while anomalous circulation (i.e. an unusually pronounced ridge) is certainly contributing to the pattern of unusual warmth it is not, alone, an adequate explanation for record-breaking heat. That's the key point here...
Thanks for answering my comment. Much appreciated.
Question 6:
How does a temp increase on the global scale cause spot increases in the regional areas (i.e. Central US)? Are there other intermediate steps that have to occur in the atmosphere (cause and effect) in order for these heat waves to happen? How can I use atmospheric physics to describe what is happening (AGW = regional heat waves) Thanks for your time!
In order for AGW to directly cause the heat waves like current one in the US, would the increase in temp need to be caused by an increasingly stronger continental ridge cause by a change in the wave pattern around the globe? In other words, is AGW causing the wave pattern to change? Is this a correct supposition?
Scott--fair question. But no, you can't explain the record-breaking warmth by atmospheric circulation alone. We've had very similar circulation anomalies in mid-summer in the past, and they didn't lead to the same level of warmth. So while anomalous circulation (i.e. an unusually pronounced ridge) is certainly contributing to the pattern of unusual warmth it is not, alone, an adequate explanation for record-breaking heat. That's the key point here...
Thanks for answering my comment. Much appreciated.
Question 6:
How does a temp increase on the global scale cause spot increases in the regional areas (i.e. Central US)? Are there other intermediate steps that have to occur in the atmosphere (cause and effect) in order for these heat waves to happen? How can I use atmospheric physics to describe what is happening (AGW = regional heat waves) Thanks for your time!
Sure thing Scott, happy to do so. In short, the warming is not uniform in space or time, there is much variability and much noise. In any given year, ENSO, the NAO, and other factors will make certain places warmer than they otherwise would have been, and other places colder. But over time nearly everyplace warms up, and the pattern of warming from greenhouse gases isn't uniform. You get more warming over continental interiors and more warming in the Arctic owing to ice-related feedback mechanisms (both are actually evident in the pattern we've seen this year).
There is a great animation based on the NCAR CCM climate model projections that shows all of this very nicely (sorry its about 37 MB):
There is a great animation based on the NCAR CCM climate model projections that shows all of this very nicely (sorry its about 37 MB):
http://climate.envsci.rutgers.edu/CCM250yrWarmingOrtho_long.mpg
Question 7:
How much CO2 is absorbed into the oceans?
Thus far about 30% of CO2 appears to have been taken up by the ocean, and about 15% by the terrestrial biosphere, so that the "airborn" fraction, i.e. the CO2 that is remaining in the atmosphere is about half of what we've emitted. One of the worries is that these carbon "sinks" become saturated and the CO2 begins to build up even faster.
Question 7A:
Does an increase in CO2 in the oceans change the thermocline circulation over time? Thanks again...Scott
I don't know of any direct influence on the CO2 itself, per se, on the thermohaline circulation, but the *warming* is predicted to influence the circulation (e.g. through the freshening of the upper ocean due to high-latitude melting ice).
Question 7B:
Are these carbon sinks re-radiated back into the atmosphere or do they stay in the ocean? If so, at what rate?
The carbon sinks can eventually lose their ability to take up carbon, in which case they might even become sources--and in that sense, yes they can actually even lose some of the previously stored carbon to the atmosphere. there is one of the concerns, for example, of the melting of the permafrost and potential release of methane that had been stored there for many thousands of years.
Question 7C:
Why are surface temps used to measure global temps and not satellite UAH numbers?
Both are used, but satellite temps are an integrated measure of lower atmosphere not surface. And unfortunately, UAH record has been compromised by so many errors over the years (sign error and algebraic error that led to an incorrect conclusion regarding the *sign* of the warming trend---I discuss this in my book) that nobody uses it. There are other estimates (e.g. RSS) based on same satellite data (now that UAH finally released a few years ago), and these reaffirm the surface record indicating that surface and lower atmosphere both warming. The instrumental record is of course much longer, and hence more useful for assessing long-term trends...
Question 7:
How much CO2 is absorbed into the oceans?
Thus far about 30% of CO2 appears to have been taken up by the ocean, and about 15% by the terrestrial biosphere, so that the "airborn" fraction, i.e. the CO2 that is remaining in the atmosphere is about half of what we've emitted. One of the worries is that these carbon "sinks" become saturated and the CO2 begins to build up even faster.
Question 7A:
Does an increase in CO2 in the oceans change the thermocline circulation over time? Thanks again...Scott
I don't know of any direct influence on the CO2 itself, per se, on the thermohaline circulation, but the *warming* is predicted to influence the circulation (e.g. through the freshening of the upper ocean due to high-latitude melting ice).
Question 7B:
Are these carbon sinks re-radiated back into the atmosphere or do they stay in the ocean? If so, at what rate?
The carbon sinks can eventually lose their ability to take up carbon, in which case they might even become sources--and in that sense, yes they can actually even lose some of the previously stored carbon to the atmosphere. there is one of the concerns, for example, of the melting of the permafrost and potential release of methane that had been stored there for many thousands of years.
Question 7C:
Why are surface temps used to measure global temps and not satellite UAH numbers?
Both are used, but satellite temps are an integrated measure of lower atmosphere not surface. And unfortunately, UAH record has been compromised by so many errors over the years (sign error and algebraic error that led to an incorrect conclusion regarding the *sign* of the warming trend---I discuss this in my book) that nobody uses it. There are other estimates (e.g. RSS) based on same satellite data (now that UAH finally released a few years ago), and these reaffirm the surface record indicating that surface and lower atmosphere both warming. The instrumental record is of course much longer, and hence more useful for assessing long-term trends...
