Category Archives: Q & A on Climate Science

Q&A On Two Climate Science Questions – A Contribution By Tom Stohlgren

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Tom Stohlgren who is Invasive Species Science Branch Chief, U.S. Geological Survey of the Fort Collins Science Center, and Senior Scientist and Affiliate Faculty at the Natural Resource Ecology Laboratory (NREL), Colorado State University (CSU).

The CSU NREL website provides the following short summary of Tom’s biography in which his professional focus is

Assessing landscape-scale and regional effects of land use change on natural ecosystems, and monitoring the effects of multiple stresses on native and exotic plant diversity. (2) linking information at landscape-, regional-, national-scales. (3) Developing GIS-based, predictive spatial and temporal ecological models to guide management of public lands. (4) Teaching courses in ecology and training graduate students.

Tom’s climate science contributions include his book  from Oxford University Press entitled “Measuring Plant Diversity  Lessons from the Field”. 

The Q&A with Tom follows:

1. Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Tom’s Answer

I don’t understand this question. These are all loosely defined terms, often misused terms, and definitions are confusing and scale dependent (in space and time). If climate change is taken in it’s broadest way possible, then the other terms would be subsets. I have no idea what you mean by second question. Does “It” dominate climate change? This answer would depend on the metrics used to define dominance, and they also would be definition-dependent and scale dependent (in space and time). We can say with certainty that the earth has had periods of warming and cooling over time. We can say with some certainty that we are in a general warming trend globally over the past 150 years or so, with a lot of annual and regional variation. We, as a group, have wonderful powers of hindsight.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Tom’s Answer

I have seen no peer-reviewed publications that have accurately predicted regional climate (and precipitation and temperature seasonality) for several regions across temporal scales from 10 to 50 years. I am not overly familiar with very recent literature on the topic, so please send me a paper proving predictive power (with independent validation) if it exists. We, as a group, have very poor predictive capabilities on scales that matter.

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Q&A On Two Climate Science Questions – A Contribution By Kevin Trenberth

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Kevin Trenberth of NCAR.  As written at the NCAR website

Dr. Kevin E. Trenberth is a Distinguished Senior Scientist in the Climate Analysis Section at the National Center for Atmospheric Research. From New Zealand, he obtained his Sc. D. in meteorology in 1972 from Massachusetts Institute of Technology. He was a lead author of the 1995, 2001 and 2007 Scientific Assessment of Climate Change reports from the Intergovernmental Panel on Climate Change (IPCC), and shared the 2007 Nobel Peace Prize which went to the IPCC…….He is a fellow of the American Meteorological Society (AMS), the American Association for Advancement of Science, the American Geophysical Union, and an honorary fellow of the Royal Society of New Zealand. In 2000 he received the Jule G. Charney award from the AMS and in 2003 he was given the NCAR Distinguished Achievement Award. He edited a 788 page book Climate System Modeling, published in 1992 by Cambridge University Press. He has published over 470 scientific articles or papers, including 47 books or book chapters, and over 206 refereed journal articles and has given many invited scientific talks as well as appearing in a number of television, radio programs and newspaper articles. He is listed among the top 20 authors in highest citations in all of geophysics.

The Q&A with Kevin follow:

1. Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Kevin’s Answer

Global warming usually refers to the human influence on climate.  Some think it refers to just global temperatures.  It doesn’t.  A good indicator is rise in sea level. It is but one component of climate change but the most predictable part and a dominant component on a 20 year time horizon and longer.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Kevin’s Answer

Not a very well posed question. Global climate models deal with all time scales. ENSO is predictable for up to a year or so.  The NAO is largely a natural atmospheric mode and has limited predictability of a few weeks. The PDO is not independent of ENSO and it depends on what is meant by “PDO”.  If it is truly “decadal” then it has persistence predictability for 5 years or so. Climate models have varying degrees of success in simulating these and prediction requires initialization of the ocean and other climate components.  That is very much experimental science but there is considerable promise, as outlined in a recent article in BAMS by Jim Hurrell and colleagues (which you wrote a comment on that failed to impress me).  The ability of models to deal with modes and regional climate is part of chapter 14 of the next IPCC report.  There is promise, but models need to improve.

Postscript:  The Hurrell et BAMS paper and my Reply, that Kevin refers to, is available from

James Hurrell, Gerald A. Meehl, David Bader, Thomas L. Delworth, Ben Kirtman, Bruce Wielicki Bulletin of the American Meteorological Society, 2009: A Unified Modeling Approach to Climate System Prediction; Volume 90, Issue 12 (December 2009) pp. 1819-1832

Pielke Sr., R.A., 2010: Comment on ” A Unified Modeling Approach to Climate System Prediction”, Bull. Amer. Meteor. Soc.,  91, 1699–1701, DOI:10.1175/2010BAMS2975.

with my weblog post discussing this at

Publication Of “Comments on ‘A Unified Modeling Approach to Climate System” By R. A. Pielke Sr And “Reply” By Hurrell Et Al 2010

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Q&A On Two Climate Science Questions – A Contribution By Bill Parton

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Bill Parton of the Natural Resource Ecology Lab at Colorado State University. As written at Green Experts at Colorado State Bill is a

“….senior research scientist at NREL (Natural Resource Ecology Laboratory), [who] is studying how different crops used for biofuels have varying effects on decreasing the amount of greenhouse gas emissions into the atmosphere. Parton also studies the effects global warming will have on the eastern plains of Colorado, Wyoming, Montana and the western parts of North and South Dakota. Additionally, he has experience studying the potential impact of climatic changes for forest and savanna systems on local, regional and global scales.

Parton, who’s spent the past 38 years working on the development of ecosystems models, was elected as a Fellow of the American Geophysical Union in 2007. The number of Fellows elected each year is limited to no more than 0.1 percent of the total membership of AGU.

The Q&A with Bill follows:

1.  Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Bill’s Answer

The answer to the first question is that climate change includes many different aspects such as changes in precipitation, cloud cover, dew points, and temperature  and changes in variability of the climate system. Climate warming is just one aspect of the climate system as you know.

It certainly seems to me that climatic variability is definitely increasing. Look at the changes in snow during the last three years. Large snowfall last year, low snowfall two years ago, and the lowest early season snowfall I have ever seen this year. There was no snow at my mountain cabin( 10500 ft ) this year for Christmas. Lowest snowfall in the last 30 years at our cabin.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Bill’s Answer

I have not worked extensively with evaluating how well GCM models predict changes in ENSO , NAO,  and PDO. My suface knowledge would indicate that the models have been getting better at predicting ENSO etc dynamics  and that there is substantial effort to improve the ability of GCM models to predict ENSO etc dynamics.

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Q&A On Two Climate Science Questions – A Contribution By Ben Herman

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Ben Herman. As written at the University of Arizona website

Dr. Herman is primarily concerned with the optics of atmospheric aerosols, polarization and scattering, and the application of inversion techniques to analyze remote sensing data obtained from aircraft and satellites. Currently, he is working on several satellite based remote sensing projects to monitor ozone, temperature, water vapor and aerosols from space.

The Q&A with Ben follows:

1.  Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Ben’s Answer

In my opinion, “global warming” should be considered a subset of climate change, but in most peoples minds, I believe they immediately associate climate change with global warming. This is probably due, in part at least, to the gradual change on the part of the climate community to use the words “climate change” in place of global warming, and then resort to discussions relating primarily to “global warming”. This then merges the two terms into one in the minds of most lay people.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Ben’s Answer

I’m not sure that there exist any strong evidence that the models are able to accurately predict either changes in large scale ocean and atmospheric circulation  patterns, or changes in statistics of these patterns.  The variations of the global temperature data during the past 10-15 years as compared to the predicted change is one example of a non-accurate forecast of temperature. I have seen little evidence that large scale circulation patterns such as ENSO, PDO, etc can be predicted over short time periods, let alone 50-100 year periods. I also think there are serious questions as to the accuracy of feed back processes and errors here could cause major errors in long term predictions. Finally, the ability to predict precipitation changes, even over short time periods, is very questionable. So, while overall it is clear that the introduction of “greenhouse gases” into the atmosphere must result in a warming of the troposphere, I can make that prediction without a model. The question as to how much warming will result, and how this will effect overall circulation patterns, precipitation, etc. are questions that I believe have not, to date, been answered with any confidence.

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Q&A On Two Climate Science Questions – A Contribution By Mike MacCracken

As part of my weblog posts, I am inviting internationally well-respected climate science colleagues to answer two questions that I have posted to them.  Today’s scientist is Mike MacCracken. As written at the website of the Climate Institute.

Michael MacCracken has been Chief Scientist for Climate Change Programs  with the Climate Institute in Washington DC since 2002; he was also  elected to its Board of Directors in 2006. Both of these positions are  held on a volunteer basis.

The Q&A with Mike follow:

1.  Is global warming (and cooling) a subset of climate change or does it dominate climate change?

Mike’s Answer

I would say that human-induced climate change is a subset of overall changes in climate over Earth’s history. There are a number of human-induced influences, some of which exert warming and some of which exert cooling influences–and these can have different time scales. Over the next 100 years, the emissions resulting mainly from fossil-fuel based combustion (so CO2, SO2, BC, CH4, and other emissions contributing to tropospheric ozone) are virtually certain to exert a dominant warming influence on sub-continental to global scales (and this is frequently referred to as global warming, although the climatic changes that are induced go far beyond just warming on the global scale). In some local to sub-continental regions land cover change–some due directly to humans and some due to changes in climate induced by other factors, especially due to ongoing use of fossil fuels–may lead to comparable warming or even to cooling on time scales of decades, and so cannot be ignored.

2. What evidence exists that the multi-decadal global climate models can skillfully predict i) the real-world observed behavior of large-scale atmospheric-ocean circulation features such as ENSO, the NAO, the PDO, ect. and ii) CHANGES in the statistics (patterning and in time) of these circulation features?

Mike’s Answer

With or without models, we do not have “predictive skill” of Earth system oscillations on time scales of multiple decades–or even multiple years– and it is not clear, given the nonlinearities of the system, that predictive skill can be achieved. It is also not clear that lacking this skill has anything to do with “projections” of how the climate will be changed by human activities over periods of many decades to many centuries–that is, to the time scales related to the changes in climate being induced by the increasing concentrations of CO2 and other greenhouse gases. The inherent variability of the natural oscillations does make extracting the signal due to changes in land cover considerably more difficult.

I defer to the IPCC analyses (AR4 and pending AR5) on the growing, but limited capabilities of the global models to project (they do not “predict” as my comment on your note in Climatic Change attempted to clarify several years ago–so you should know better than to be saying “predict”) the present and future changes in the statistics of various Earth system oscillations (and what, in some cases, our limited observational record suggests, perhaps incorrectly, may be oscillations). I would only note that I don’t consider this limitation to accurately simulate the current statistics of Earth system oscillations to mean that the models are not reasonably projecting how the mean state of the global climate is likely to change over periods of several decades and more due to combustion of fossil fuels, but do think this limitation makes it more difficult to project the combined changes of fossil fuel combustion and land cover change on regional scales.

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Recommended Reading – “On the Skeptical Science Post ‘Pielke Sr. Misinforms High School Students’ By Bob Tisdale

 

Bob Tisdale – Climate Observations has another very informative weblog post titled

On the Skeptical Science Post “Pielke Sr. Misinforms High School Students”

It provide an effective rebuttal to the post on Skeptical Science.

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E-Mail Exchange With Josh Willis On The Ability To Monitor The Transfer Of Heat In The Oceans To Levels Below 700m

Several weeks ago, I had an interesting exchange of viewpoints with Gavin Schmidt and a few others on Real Climate which I summarized in my post

Response To Gavin Schmidt’s Post Of October 3 2011 “Global Warming And Ocean Heat Content”

My Recent Discussion with Gavin Schmidt On Real Climate

One of the issues is whether the existing Argo network can resolve the transfer of heat through the upper 700m of the ocean. I contacted Josh Willis of Jet Propulsion Laboratory and have (with his permission) reproduced them below (with minor edits and the insertion of the abstract of a paper and the figures referred to).

My E-Mail

Hi Josh

In a discussion on Real Climate, this question came up from Gavin  Schmidt in response to my comment  [http://www.realclimate.org/index.php/archives/2011/10/global-warming-and-ocean-heat-content/comment-page-3/#comment-216615]

My Comment on Real Climate

 On your question regarding heat transfer downward, if the models show warming at depth, why don’t you show plots as to the magnitude of its fluxes over time and space through the upper 700m of the ocean. Then one could look at the observations to see if this flux is there with the same pattern and magnitude as the real world data.  I assume our disagreement is in the form of these fluxes. If they are diffuse and distributed across the upper oceans, I agree they would be hard to see in the Argo data. However, if this transfer occurs in globs  associated with mesoscale and larger ocean circulation features (as suggested in the ECMWF data), we should clearly see this movement of  heat.

 [[Gavin’s] Response: Model estimates of total heat flux through 700m are possible of course, but non-trivial to compute (including effects of the resolved circulation, isopycnal diffusion, and vertical mixing) – though this might well be worth doing for the CMIP5 models. However, I don’t have the answers handy. But I have no confidence that the observations will be sufficient to distinguish the anomalous heat flux from the climatological mean with sufficient precision to be helpful. If you think it is,please point to a study that has attempted this. – gavin]

Can you let me know if this has been done from the observations?

Best Regards
Roger

Josh’s Reply

Hi Roger,

 The way I would answer this is that we can probably diagnose the amount of warming between 700 and 2000 m in the Argo data for the past 5 to 7 years. Using the data to determine the cause of this, however, can be tricky.  For example, if an isotherm at 1000 m is depressed in one region by 10 meters, is this caused by a simple downward advection of the isopycnal, or is it due to vertical or horizontal mixing with a nearby warm water mass?

 Questions like this can be difficult to answer with the Argo data. Nevertheless, with some basic knowledge of the local oceanographic conditions and use of additional data, like salinity and horizontal advection, it might be possible to tease apart the causes of this temperature change.  There are some efforts to do this for the abyssal warming signal published by Purkey & Johnson, by asking the question: how big of a reduction in bottom water formation would be needed to account for the observed warming of the abyssal waters?  I’m not sure if that work is published yet, however.

Hope this helps.

Cheers,

Josh

My E-Mail

Hi Josh

 This is helpful; thanks!

 I do have several questions/comments.

 Regarding

 ” if an isotherm at 1000 m is depressed in one region by 10 meters, is  this caused by a simple downward advection of the isopycnal, or is it due  to vertical or horizontal mixing with a nearby warm water mass?:

 I agree this could be difficult. However, in terms of moving heat through  the entire upper 700m, the critical question, in my view, is whether the Argo network has the spatial and temporal resolution to see coherent regions of warm and cold anomalies e.g. seen in  http://www.ecmwf.int/products/forecasts/d/charts/ocean/real_time/xzmaps/ ?

 Or are they there only for one sampling period and than gone?

 If it is the former, we should be able to track these “globs” of  anomalies.

 Have you (or anyone) looked at the coherency of these anomalies over time?

 In the same context, if one integrated horizontally at different levels  over regions in each ocean, the region-time integrated movement of heat upwards and downwards would seem to be possible IF the space and time  resolution of Argo is good enough. If not, what would need to be added to the Argo network to accomplish this?

 It seems this subject would benefit from a paper.

 With Best Regards

 Roger

Josh’s Reply

Hi Roger,

You are more than welcome to post these comments.  For interannual or longer time scales, the Argo networks should easily resolve the large-scale movement of heat between the upper (<700 m) and mid-depth (700 to 2000 m) layers of the ocean.  For interannual signals the global coverage is now quite good:

http://www-hrx.ucsd.edu/www-argo/statusbig.gif

So in short, yes, the “globs: of heat anomalies that change on yearly time scales are resolved by Argo.  There is now a vast literature on the use of Argo data (more than 150 papers per year).  Here is one of interest:

Roemmich, D., and J. Gilson (2011), The global ocean imprint of ENSO, Geophys. Res. Lett., 38, L13606, doi:10.1029/2011GL047992.

[the abstract of this paper reads

“The ENSO-related spatial patterns and global averages of ocean temperature, salinity, and steric height are estimated from over 7 years of Argo data, 2004–2011. Substantial extratropical variability is seen in all variables in addition to familiar tropical ENSO signals. Surface layer (0–100 dbar) and subsurface (100–500 dbar) temperature variations are both important in determining steric height and sea surface height patterns. For the two years prior to the 2009 El Niño, the upper 100 dbar of the ocean gained 3.3 × 1022 J yr−1 of heat, while the 100–500 dbar layer lost a similar amount. The ENSO-related vertical redistribution of globally-averaged heat content between surface and subsurface layers, occurring throughout the record, is due primarily to changes in the east-west tilting of the equatorial Pacific thermocline. The large temperature changes in the individual layers mask the smaller vertically-averaged temperature change, in which the ocean loses heat when the surface layer is anomalously warm and gains heat when the surface layer is cool.”]

Cheers,
Josh

My E-Mail

Hi Josh

 Thank you for the quick reply. This is very helpful.

 I guess the remaining question is whether significant amounts of heat could be transferred below 700m without being seen in the upper 700m? The curious conclusion of recent accumulation but not in the past; e.g. see

http://bobtisdale.wordpress.com/2011/10/24/introduction-to-the-nodc-ocean-heat-content-anomaly-data-for-depths-of-0-2000-meters/

is curious [Bob’s figure is reproduced below].

This accumulation started when Argo came online. Any comments you have on this issue would be welcome.

The paper you sent is quite relevant to this discussion!

Best Regards

Roger

Josh’s Reply

This is a tough question to answer, and I would say the jury is still out over how quickly the 700 to 2000 m layer can warm (or cool).  I think we need more Argo data and more time with the data that we have before we say for sure…

Cheers,
Josh

Also, Josh alerted us to the video of his presentation

Hot Water: The Oceans and Global Warming

with the abstract

Water covers nearly 70 percent of its surface, so it’s no wonder that the world’s oceans play such an important role in global climate changes. As the planet heats up, the oceans wind up being by far the biggest reservoir for taking up the extra heat. This talk will cover the ins and outs of global warming as they pertain to the world ocean.

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