I have reposted a blog post from Skeptical Science along with my responses below.
Posted on 21 September 2011 by dana1981
On his blog in response to our post One-Sided ‘Skepticism, Roger Pielke Sr. asked SkS to respond to some questions. We would like to note that these questions are totally unrelated to the initial discussion initiated by Dr. Pielke’s unsubstantiated criticism of SkS (see Chasing Pielke’s Goodyear Blimp). However, in the interest of establishing what we hope will be a productive discourse, we have agreed to answer Dr. Pielke’s questions.
Dr. Pielke’s questions are underlined in the text below, and the answers from SkS follow.
1. Of the two hypotheses below, which one do you conclude is correct? (see Dr. Pielke’s post for the two hypotheses offered)
The two aren’t mutually exclusive, and both are correct. CO2 is the dominant radiative forcing causing the current global energy imbalance.
R.Pielke Sr. Response –
First, let me thank you for moving on to actual science issues.
In response to your first answer, they actually are separate hypotheses and only one of them can be correct.
We discuss this in
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.
where we wrote
“Hypotheses 2a and 2b are two different oppositional views to hypothesis 1. Hypotheses 2a and 2b both agree that human impacts on climate variations and changes are significant. They differ, however, with respect to which human climate forcings are important………. we suggest that the evidence in the peer- reviewed literature (e.g., as summarized by National Research Council (NRC) ) is predominantly in support of hypothesis 2a, in that a diverse range of first-order human climate forcings have been identified.”
“We therefore conclude that hypothesis 2a is better supported than hypothesis 2b, which is a policy that focuses on modulating carbon emissions. Hypothesis 2b as a framework to mitigate climate change will neglect the diversity of other, important first- order human climate forcings that also can have adverse effects on the climate system. We urge that these other climate forcings should also be considered with respect to mitigation and adaptation policies.”
“The evidence predominantly suggests that humans are significantly altering the global environment, and thus climate, in a variety of diverse ways beyond the effects of human emissions of greenhouse gases, including CO2. Unfortunately, the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment did not sufficiently acknowledge the importance of these other human climate forcings in altering regional and global climate and their effects on predictability at the regional scale. It also placed too much emphasis on average global forcing from a limited set of human climate forcings.
Again, the two perspectives are not mutally exclusive, and both are correct. As Hulme notes, they are simply two different framings. In terms of climate policy, the second framing is probably more appropriate, as addressing climate change will involve more than just CO2 emissions reductions.
R.Pielke Sr. Response –
If the second framing is more appropriate, we have made progress towards agreement as that framework fits with hypothesis 2a. I also suggest you contact Mike Hulme for his view whether both perspectives can be “correct”.
3. What is your preferred diagnostic to monitor global warming?
SkS doesn’t have a preferred diagnostic – all lines of evidence must be taken into account. It’s important to look at all the data in totality to monitor global warming (surface temperature, ocean heat content, atmospheric temperature, TOA energy imbalance, sea level rise, receding ice, etc.).
R.Pielke Sr. Response –
Global warming or cooling involves changes in Joules of heat in the climate system. This involves changes in heat in the oceans, land, atmosphere and cryosphere. As concluded by Jim Hansen and others, the ocean is by far the component of the climate system where the large majority of this heating and cooling occurs. Receding ice, surface temperature, atmospheric temperatures make up only a relatively small portion of global warming and cooling.
What is your best estimate of the observed trends in each of these metrics over the last 10 years and the last 20 years?
10-year trends are generally not statistically significant (see Santer et al. 2011, for example). The approximate best estimate observed trends for some of these metrics over the last ~20 years are as follows. TLT: 0.18°C per decade. Surface temperature: 0.18°C per decade. Ocean Heat Content (OHC) upper 700 meters: 6.3 x 1022 J per decade. Sea level rise: 32 mm per decade. Arctic sea ice volume: -2900 km3 per decade. Glacier mass balance: -180 mm w.e. per decade.
4. What do the models’ predict should be the current value of these metrics?
The surface temperature change is roughly consistent with model predictions, though perhaps a bit on the low end. The predicted TLT trend is approximately 0.26°C per decade. Sea levels are rising faster and Arctic sea ice is declining far faster than models predict.
OHC in the upper 700 meters increased more than the models expected from 1961 to 1999, and has increased less than models project since 2003. There are a number of factors that may explain the recent discrepancy:
- as noted above, this is too short of a timeframe for a valid statistical evaluation;
- models generally do not take the increases in aerosol emissions over this period into account;
- there is a wide range of estimates of upper 700 meter OHC trend since 2003, varying by nearly two orders of magnitude; and
- the oceans are much deeper than 700 meters, and the so-called “missing heat” may very well reside in the deeper oceans (i.e. see Meehl et al. 2011).
One reason that we like to rely on multiple lines of evidence, rather than depend on one single indicator, is that any one can be wrong. The history of the UAH measurements comes to mind: the measurements were in conflict with other methods for tracking temperature change (and with climate model projections) for over a decade; eventually, most of the discrepancy was resolved (in favor of the models) only after very subtle analysis of the physical behavior of the instruments.
R.Pielke Sr. Response –
The oceanographers who work with the ocean heat data are convincing (at least to me and a number of other colleagues) that since the completion of the Argo network, it is a robust metric (within defined uncertainty bars) such as Josh Willis placed on the figure he provided me for the article
Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55. https://pielkeclimatesci.files.wordpress.com/2009/10/r-334.pdf
5. What are your preferred diagnostics to monitor climate change?
That depends on how “climate change” is defined, but again, it is necessary to look at all lines of evidence and data.
R.Pielke Sr. Response –
You avoided answering this question. This is actually an essential issue to resolve. The NRC (2005) report [http://www.nap.edu/openbook.php?record_id=11175&page=200] defines climate change as
“The system consisting of the atmosphere, hydrosphere, lithosphere, and biosphere, determining the Earth’s climate as the result of mutual interactions and responses to external influences (forcing). Physical, chemical, and biological processes are involved in interactions among the components of the climate system. ”
This is much broader than just global warming and cooling. Please clarify your view.
6. Is global warming (and cooling) a subset of climate change or does it dominate climate change?
Again, that depends on how “climate change” is defined. Long-term global temperature and climate changes are both ultimately caused by global energy imbalances.
R.Pielke Sr. Response –
The recognition that climate changes can occur without any global energy imbalance is central to the much needed broader view of how humans are altering the climate system. Please clarify what is “climate change” in your view.
Now that we have answered your questions, there are a few issues on which we would like to understand your perspective, Dr. Pielke.
SkS Questions for Dr. Pielke
1. Approximately what percentage of the global warming (increase in surface, atmosphere, ocean temperatures, etc.) over the past 100 years would you estimate is due to human greenhouse gas emissions and other anthropogenic effects? And the past 50 years?
This is a good question. It is a still incompletely understood mix of a variety of human caused radiative forcings (e.g. CO2, methane and several other greenhouse gases, land use/land cover change, black carbon (soot), sulphates, and other aerosols) and natual climate variations.
Several years ago I did a back of the envelope estimate and came up that ~26% of the positive radiative forcing was from CO2; see slide 12
Pielke, R.A. Sr., 2006: Regional and Global Climate Forcings. Presented at the Conference on the Earth’s Radiative Energy Budget Related to SORCE, San Juan Islands, Washington, September 20-22, 2006. https://pielkeclimatesci.files.wordpress.com/2009/09/ppt-69.pdf.
This number certainly changes through the last 100 and the last 50 years, and remains uncertain.
The complexity of these radiative forcings is discussed in some detail in NRC (2005) –
http://www.nap.edu/openbook/0309095069/html/. Despite the vigor with which you criticize Roy Spencer, he actually has been instrumental in elevating our awareness that natural variations in cloud cover, as a result of temporal variations in atmospheric circulation features, as causing long term variations in the TOA radiative imbalance.
2. Do you find Spencer, Lindzen, and Christy’s arguments that equilibrium climate sensitivity is in the ballpark of 1°C or less for doubled atmospheric CO2 plausible? If so, how do you reconcile this low climate sensitivity with the paleoclimate record, for example needing to explain ~5°C swings in average global surface temperature between glacial and interglacial periods (i.e. see the figure below from Hansen and Sato 2011)?
I do not find the glacial and interglacial periods as useful comparisons with the current climate since when we study them with models, they have large differences in imposed terrain (e.g. massive continetal glaciers over the northern hemisphere which will alter jet stream features, for example).
In any case, I find the discussion of the so-called “climate sensitivity” by all sides of this issue as an almost meaningless activity. I posted on this in
So-Called “Climate-Sensitivity” – A Dance On The Head Of A Pin –
3. Do you agree that continuing on our current business-as-usual emissions path presents an unacceptable (in your opinion) risk to the biosphere and to human society in general within the next century?
Of course. The emission of CO2 into the atmosphere, and its continued accumulation in the atmosphere is changing the climate. We do not need to agree on the magnitude of its global average radiative forcing to see a need to limit this accumulation. The biogeochemical effect of added CO2 by itself is a concern as we do not know its consequences. At the very least, ecosystem function will change resulting in biodiversity changes as different species react differently to higher CO2. The prudent path, therefore, is to limit how much we change our atmosphere.
By continuing to argue on global warming and its magnitude, I feel you, and others, are missing an opportunity to build up a larger consensus on how to properly deal with the myraid ways we are altering the climate and the environment, in general. Even if there were no global warming (or even cooling) in the coming decades, we still need to limit how much we change the environment (including land use change, nitogren deposition, CO2 etc).
4. Do you agree that continuing on our current business-as-usual emissions path presents an unacceptable (in your opinion) risk to marine ecosystems in the form of ocean acidification within the next century?
Regardless of whether we reduce the alkalinity of the oceans (since there may be buffering from the added CO2 through mixing from below) we will be altering ecosystem function both in the oceans and in the atmosphere. Since we do not know the consequences of doing this, the smart thing to do is to work towards reducing the extent we alter the chemisty of the oceans and the atmosphere.
5. Do you think that we should begin to move towards a low-carbon economy, thereby reducing anthropogenic GHG emissions?
I am very much in favor of energy sources which minimize the input off gases and aerosols into the atmosphere. Much of my career has been involved with reducing air pollution (both in research and in policy). What we should move towards is an economy with as small a footprint on the natural environment as possible.
In terms of how to do this with respect to carbon emissions, I completely agree with my son’s perspective as he presents in The Climate Fix – http://theclimatefix.com/