The Other Discernable Influence
July 25th, 2005Posted by: Roger Pielke, Jr.
In his testimony last week NCAR’s Jim Hurrell made an interesting comment, “… it should be recognized that mitigation actions taken now mainly have benefits 50 years and beyond now.” I wrote here last week that, “This point would seem to be generally appreciated by experts in climate science and policy but is generally lost in the more general debate.” But after talking to some folks about my post, it seems that this point is worth some further examination.
So let me pose a few questions to the climate science community. (And in particular, if the RealClimate folks would take a crack at it I’d appreciate it.) These are not economics questions or policy questions, but questions of climate science with relevance to consideration of policy options. And if these questions are dealt with by the IPCC or in the published literature, I am unaware of it, so pointers to references are also appreciated.
(a) If anthropogenic CO2 emissions we instantaneously halted on 31 December 2005, how long would it be before the scientific community could detect and attribute a discernable influence of this policy on the climate system? Specifically, please use the following four variables: atmospheric CO2 concentrations, global average temperature, sea level rise, and extreme weather events (heat waves, hurricanes, floods, etc.).
And there are some obvious permutations also worth considering, such as for example (b) halting CO2 emissions in 2020, (b) cutting CO2 to 1990 levels by 2012, and (c) cutting global CO2 emissions by 50% by 2030.
All replies welcomed, Thanks!
July 25th, 2005 at 4:05 pm
Roger,
You should pay more attention to http://ccc.atmos.colostate.edu/blog/ which I believe is written by your father. His comments to date indicate (1) that the models have no predictive value, and (2) the committee stacked the testimony by dropping him at the last moment and substituting Hurrell.
July 25th, 2005 at 5:12 pm
Paul- Thanks for your comment. This is off subject, and one that I’d really like to here some thoughtful responses to, so my reply is quick. (1) I don’t think my father said anything about value, but instead skill. He has written widely that models have plenty of value. (2) Yes, of course hearings are stacked, usually some witnesses are selected by the majority and some by the minority. This is business as usual. I’d expect that, just as with the current Administration and their troubles with the advisory committee empanelment process, Congress too, should be more careful in issue and retracting invitations. If you’d like to follow up, please do so at Climate Science, Thanks!
July 25th, 2005 at 9:17 pm
“(a) If anthropogenic CO2 emissions we instantaneously halted on 31 December 2005, how long would it be before the scientific community could detect and attribute a discernable influence of this policy on the climate system? Specifically, please use the following four variables: atmospheric CO2 concentrations, global average temperature, sea level rise, and extreme weather events (heat waves, hurricanes, floods, etc.). ”
By “instantaneously halted,” I’m assuming you mean, “immediately go to zero.”
1) With zero emissions of CO2, atmospheric CO2 concentrations would presumably no longer rise. In fact, they would presumably even fall slightly. That should be noticed immediately.
2) Current thinking is that there’s 0.5 degrees Celsius warming stored in the oceans. With surface temperatures currently rising at approximately 0.17 degrees Celsius per decade, that’s about 3 decades of warming. But perhaps the warming wouldn’t be as fast as it is currently. In any case, I would say that the temperature different temperature trend would be recognized in the 10-30 year time frame. (Not less than 10 years, because 0.17/decade is less than annual fluctuations.)
3) My guess for sea level rise would also be in the 10-30 year time frame, for the same reason as determining temperature rate change.
4) Extreme weather events:
a) Heat waves, I don’t know.
b) Hurricanes, floods: My understanding is that there has not been any trend yet detected. So what would presumably happen is that the “no trend” would continue. This would be as opposed to the expected trend of stronger hurricanes (for example). But the AMOUNT that hurricanes are expected to be stronger is so small (less than 10 percent increase in wind speed) that it seems like it would take an awfully long time to say that the “no trend” was different from the expected trend. My (crude) estimate would be not less than 30 years to discern the effect (for hurricane intensity).
July 25th, 2005 at 9:29 pm
I have a few of questions I would also like answered.
Firstly. What is the probability that the Earth will be moving into an Ice Age by 2100?
I ask this because from what I have read at various Climate related sites that Interglacial periods last approximately 10,000 years and we are now at 10,000 years. All I need would simply be a statistical calculation i.e. if we were 5000 years into an Interglacial period the probability of an Ice Age within the next 100 years would be low. Since we are at 10,000 years I would have thought the probability considerably higher. Is it a 1 in 1000 or 1 in 10 chance. If after all our effort to stabilise temperature the earth starts to dramatically cool what should we do, try and make it warmer?
This is asked not because I have a doubt about climate science but more a doubt about our ability to “control” climate.
I fully accept that we do “effect” our environment/weather/climate, but I am not so convinced we have the ability to “control” our climate in any meaningful way. If we do nothing about CO2 climate “events” will happen, if we do something about CO2 (Kyoto) climate “events” will also happen.
This leads to my second question. How convinced are we that any action we take will have a Net positive benefit for mankind? In either scenario, do something about CO2 or do nothing, there will be winners and losers we can not “change” so that there are just winners. Who decides who the winners should be? Should Peoples in higher latitudes “win” or those closer to the equator? Northern Hemisphere or Southern? Do we try to stabilise CO2 at 1990 levels, at pre industrialised levels or at some other level we pick e.g. 400ppm? Which one is the “best”? If after these descisions are made will anybody notice a difference?
This brings me to my final question. Roger in an earlier post highlighted a question raised at realclimate “What if the Hockeystick is wrong?”. Well I would like to raise a similar what if. What if CO2 is not the problem? What if is is solar activity or land usage or some other unsuspected phenomenon? We spend all our time, effort and money on trying to control CO2 and it turns out it wasn’t the problem after all.
Any responses will be appreciated.
July 25th, 2005 at 9:31 pm
See for example:
http://pubs.giss.nasa.gov/docs/2005/2005_HansenNazarenkoR.pdf
http://www.grida.no/climate/ipcc_tar/wg3/392.htm
But you knew that.
Why do I suspect an answer which goes, “since we don’t get immediate gratification, we should do nothing”? You appear anxious to prepare a fallback position for the denialists, morphing them into the it ain’t any use party.
I suppose I now have to endure a lecture about how with a long induction period before a change is seen any action will be politically impossible. Nonsense.
It IS politicially possible as has been shown in many of the signatories of the Kyoto Protocol who are taking action and looking to move beyond those first steps. That what is being done is not perfect is no reason to do nothing either.
I’ve endured ten years of this silliness wrt the Montreal Protocols, until finally the mixing ratios are decreasing EXACTLY AS THE MODELS PREDICTED. BFS.
July 25th, 2005 at 10:24 pm
Eli- Thanks much for your comments. The references that you provide don’t answer the questions that I’ve raised. “Do nothing” is not a policy option that you have seen advocated on this site or in my writings. The questions I have raised are perfectly fair and worth discussing. The question is not whether to act, but how. And on EU “success” with respect to Kyoto, please see this discussion:
http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000137update_on_european_g.html
Experiences with respect to actual efforts to reduce emissions is precisely why we should be having a wide-ranging discussion of policy options.
July 25th, 2005 at 11:09 pm
1 CO2 – probably a couple of months or so, certainly within a couple of years.
2 Temp – a few decades
3 Sea level – several decades/century
4 Extremes – several decades/century
All rough estimates, E&OE.
Of course all these also depend to some extent on understanding and believing that model outputs are useful – there would no doubt be sceptics who would claim it was all just natural variability, whatever happened. Also, note that being undetectable (at a certain confidence level) doesn’t mean that an effect does not exist.
July 26th, 2005 at 10:02 am
Roger Pielke Jr. also writes: “And there are some obvious permutations also worth considering, such as for example (a) halting CO2 emissions in 2020, (b) cutting CO2 to 1990 levels by 2012, and (c) cutting global CO2 emissions by 50% by 2030.”
Here are my guesses for the “50% probability values” for warming from 1990 to 2100, based on those three scenarios.
a) Halting (bringing emissions instantaneously to zero) in 2020: Approximately 0.8 degrees Celsius of warming from 1990 to 2100.
b) Cutting CO2 emissions to 1990 levels by 2012 (note: I’m assuming that they are then kept at 1990 levels for the rest of the century): Approximately 1.0 degree Celsius of warming from 1990 to 2100.
c) Cutting global emissions to 50% (of current levels…presumably in a straight-line reduction) by 2030 (and then presumably keeping them at that level for the rest of the century): Approximately 1.0 degree Celsius of warming from 1990 to 2100.
In other words, in my opinion three scenarios are almost indistinguishable from one another, in terms of the expected temperature rise from 1990 to 2100. (This is mainly because of the rise of approximately 0.2 degrees Celsius that has already occurred from 1990 to 2005, plus an assumed 0.5 degrees Celsius warming that is “in the pipeline”…i.e., which will happen even if CO2 emissions were instantaneously stopped.)
P.S. Since I didn’t express the first scenario in these terms, my estimate of the “50 percent probability” value for warming from 1990 to 2100 that would result from an instantaneous cut to zero emissions right in 2005 (and maintaining at zero) would be about 0.5 degrees Celsius. In other words, the slightly *falling* CO2 levels (resulting from zero emissions) would actually shave off the warming that has occurred from 1990 to 2005, and the only warming would be the 0.5 degrees that’s already in the oceans.
So for all four scenarios, the expected warming is somewhere between 0.5 degree Celsius (for cutting emissions to zero immediately) and 1.0 degree Celsius (for cutting emissions to 1990 levels by 2012, or for cutting emissions by 50% by 2030).
P.P.S. Note that my “50 percent probability estimate” for the temperature increase that would result from absolutely no deviation from “business as usual” is 1.2 degrees Celsius. This corresponds to industrial emissions of CO2 peaking at approximately 1.5 times their 1990 levels in 2030, and declining to approximately 0.7 times their 1990 levels by 2100.
http://markbahner.typepad.com/random_thoughts/2005/01/prujections_ipc.html
July 26th, 2005 at 10:30 am
Ross McNaughton asks:
1a) “What is the probability that the Earth will be moving into an Ice Age by 2100? Is it a 1 in 1000 or 1 in 10 chance?”
My opinion is the probablity is less than 1 in 10, but more than 1 in 1000. Just to take a very crude guess, I’d guess 1 in 100.
1b) “If after all our effort to stabilise temperature the earth starts to dramatically cool what should we do, try and make it warmer?”
In my opinion, a cooling of 2-3 degrees Celsius from the current temperature would be much, much worse than a warming of 2-3 degrees Celsius. So, yes, in my opinion, if the earth appears likely to dramatically cool, we definitely should try to stop that cooling.
2) “This leads to my second question. How convinced are we that any action we take will have a Net positive benefit for mankind?”
This is an extremely important and excellent question. I discuss this very question on my global warming website (caution: should be viewed with a pop-up blocker):
http://markbahner.50g.com/
http://markbahner.50g.com/is_it_bad.htm
To my knowledge, there has NEVER been a careful and unbiased study that asks the question: “Is there an ‘optimum’ temperature for the earth, and if so, what is it?”
Even though I haven’t formally studied the matter, my initial guesstimate going into the study would be:
1) Yes, there is an “optimum” temperature for the earth, and
2) it is somewhere between 1 degree Celsius cooler than at present and 2 degrees Celsius warmer than at present.
Any such study would involve a very significant number of “value” judgements…e.g. “Is it better to have good skiing conditions, or more pleasant days at the beach?”
P.S. I think one way that one could somewhat evaluate what the “optimum” temperature is, would be to look at movements of people within countries, and from country to country. For example, are people in the United States moving to the South or the North? What about people in Canada? Britain? And so on.
July 26th, 2005 at 1:30 pm
I am not a climate scientist, but have followed the “science” and arguments for 10 years now. Based on what I think I have learned, I would be in close agreement with all of Mark Bahner’s observations. I would like to see one additional question added to a)”How long would it take for atmospheric CO2 concentration to return to 300 ppm?” I ask this because I find atmospheric residence time estimates for a pulse of CO2 of 50 to 200 years, and the IPCC worst case SRES scenarios would require a half life in excess of 500 years. Murray Duffin
July 26th, 2005 at 11:16 pm
Roger -
May I stray briefly from discussing climate, since your wonderful hypothetical has so many implications?
If instead of halting anthropogenic CO2 emissions instantaneously on 31 December 2005 we halted them as fast as we could replace our cars, buildings and factories with radically more efficient models; and simultaneously used wind turbines, building-integrated solar, and biomass to supply our greatly reduced energy demand, much more than climate would change:
The air would be pristine. We would all be healthier. We would be much more comfortable in our quieter cars and well-insulated homes. Owning these vastly superior assets would make us wealthier. Energy security would be available to every country, and no longer be a casus belli. We would no longer worry about sending petrodollars to the Middle East or about nuclear power plant safety and security. With all these advantages, even China wouldn’t mind having wasted $18 billion on Chevron.
And Amory Lovins (cited by commenters Murray Duffin and Lynn Vincentnathan on other threads) would be happy indeed that we finally listened.
July 28th, 2005 at 3:55 pm
Murray Duffin writes, “I would like to see one additional question added to a) ‘How long would it take for atmospheric CO2 concentration to return to 300 ppm?’”
OK, the scenario is that, in the year 2020, CO2 emissions go from whatever they are at that time (my guess is about 30 percent above 1990 values) to absolutely zero. And stay that way forever. The CO2 atmospheric concentration in the year 2020 should be approximately 405 ppm.
The question is, “How long would it take for concentrations to drop to 300 ppm (from 405 ppm)?”
I’m too lazy to do a careful analysis, but currently something like 50% of the CO2 emitted by humans doesn’t show up as concentration increases in the atmosphere. And concentration in the atmosphere is increasing by about 1.8 ppm per year. So if emissions dropped to zero, concentration should *fall* by about 1.8 ppm per year. (Again, I’m too lazy to look up actual values.)
Since we’re talking about 405 ppm – 300 ppm = 105 ppm…dividing that by 1.8 ppm per year equals about 60 years. But actually, the decline would not be that steep…the decline per year should get smaller and smaller as one got closer to 300 ppm. (In fact, if you’d chosen a value of 280 ppm, which was the value before the Industrial revolution started, the answer could theoretically be “an infinite amount of time…or at least until the start of a new Ice Age.)
So my guesstimate would be not less than 60 years…nor more than a few hundred. (If you want a better estimate, you’ll have to send some money.
)
July 30th, 2005 at 5:36 pm
The difference we are discerning would not be between the present and the recent past but between the road taken and the road not taken. It is a change “large enough to be discerned” only in comparison to some alternative history. That doesn’t mean the change will be perceivable by the body politic, though, which may present a real problem.
Anyway, if I understand the question correctly, it’s easy to estimate. It took a change of about 80 ppmv CO2 to create a discernible climate shift from the preindustrial background. When your two scenarios diverge by about that much, amounting to atmospheric concentration differences of about 80 ppmv you are entering statistically different climates. That is the edge case. Comparing to the business-as-usual increases of about 1% per year, we are looking at twenty years of so.
More realistic strategies (opposed to abruptly ending all anthropogenic emissions) will take even longer to have a discernible effect even compared to a hypothetical alternative realization, one which will not be perceived by the public.
Ouch. Thanks for the exercise. That is really a very awkward result, isn’t it?
July 31st, 2005 at 2:50 pm
Michael Tobis writes, “Anyway, if I understand the question correctly, it’s easy to estimate. It took a change of about 80 ppmv CO2 to create a discernible climate shift from the preindustrial background.”
No, this is incorrect for many reasons:
1) It is not just CO2 that has contributed to the “discernible climate shift from preindustrial background.” It’s true that CO2 has gone from about 280 ppm before the industrial revolution to approximately 380 ppm today (i.e., has increased by approximately 100 ppm).
But the atmospheric methane concentration has also more than doubled, and nitrous oxide (N20) levels have increased. Also, chlorofluorocarbons are present that weren’t present at all in the “preindustrial background.” Tropospheric ozone (aka, Los Angeles type “smog”) is also higher than in the preindustrial background.
All these effects add to the forcing from carbon dioxide:
http://intl.pnas.org/cgi/content/full/95/22/12753/F2
If we take into effect *all* the greenhouse gases (and neglect aerosols…some of which are thought to cool, and some of which are thought to warm), the current “CO2 equivalent” concentration is more like 60% above the pre-industrial value, or more like 450 ppm.
2) More importantly, absent feedbacks, the world temperature does NOT respond linearly changes in CO2 concentration, i.e. each 80 ppm increase doesn’t produce an equal change in temperature. Absent feedbacks, the world temperature responds changes linearly with LOGARITHMIC changes in CO2 concentrations. From the IPCC First Assessment Report, the following equation was given for radiative forcing versus CO2 concentration:
Delta F = 6.3*ln(C/Co), where
Delta F = Change in radiative forcing in Watts/square meter,
C = Carbon dioxide concentration at the time of interest
Co = Concentration at the previous time of interest.
Plugging in values of 280 ppm and 360 ppm, we get:
delta F = 6.3 ln(360/280) = 1.58 Watts/m2
But going up 80 more ppm, from 360 to 440 ppm, produces:
delta F = 6.3 ln(440/360) = 1.22 Watts/m2.
In other words, each 80 ppm increment produces a SMALLER temperature increase (absent feedbacks).
“When your two scenarios diverge by about that much, amounting to atmospheric concentration differences of about 80 ppmv you are entering statistically different climates.”
No, that is not correct, for the reasons I gave above.
July 31st, 2005 at 3:01 pm
Michael Tobis writes, “When your two scenarios diverge by about that much, amounting to atmospheric concentration differences of about 80 ppmv you are entering statistically different climates. That is the edge case. Comparing to the business-as-usual increases of about 1% per year, we are looking at twenty years of so.”
No, this is complete rubbish. The idea that CO2 concentration increases of 1% per year (i.e. about 3.8 ppm per year) represent “business as usual” is nothing but a bald-faced lie.
CO2 concentrations have been increasing by about HALF that value over the last 20 years:
http://www.cmdl.noaa.gov/gallery/ccgg_figures/co2trend_global