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Monday, August 26, 2013

Projecting Dr Trenberth and avoiding his question

Sou | 2:08 PM Go to the first of 15 comments. Add a comment

Which Dr Trenberth?


Anthony Watts, who has written many, many articles about Dr Kevin Trenberth, forgets his name and starts calling him Kenneth (archived - later corrected version).

Source: WUWT




As Frank Kotler says, way way down in the WUWT comments:
August 25, 2013 at 6:13 pm Top post still says “Kenneth” in a couple places. We’re talking about the same guy, right? If we’re going to insist that words have meanings, getting the man’s name right might be a good start…


Predictions and projections


The WUWT-ers are having trouble working out the difference between IPCC model projections and model predictions.  Perhaps they can think of it this way.  IPCC models are used to make projections about climate (surface temperature, precipitation, ice cover etc) for a range of different scenarios.  Scenarios are largely based on emissions trajectories.  That is, if we continue on a very high rate of CO2 emissions, the average global surface temperature will rise much more than if we cut CO2 emissions.  The scenario processes for IPCC AR5 reports are described here.  There are four Representative Concentration Pathways (RCPs) that are described here.  These are:

  • RCP8.5 Rising radiative forcing pathway leading to 8.5 W/m2 in 2100.
  • RCP6 Stabilization without overshoot pathway to 6 W/m2 at stabilization after 2100
  • RCP4.5 Stabilization without overshoot pathway to 4.5 W/m2 at stabilization after 2100
  • RCP2.6 Peak in radiative forcing at ~ 3 W/m2 before 2100 and decline

The word "prediction" could be used when referring to a particular scenario as part of an "if" statement.  For example, IF we were to continue to track on or above RCP8.5 I'd predict we'd face a very challenging future!

Jimbo from WUWT posted a comment about an old blog article by Dr Trenberth.  Here is Dr Trenberth's article in full from Nature's climate feedback blog:

Predictions of climate

Posted by Oliver Morton on behalf of Kevin E. Trenberth
I have often seen references to predictions of future climate by the Intergovernmental Panel on Climate Change (IPCC), presumably through the IPCC assessments (the various chapters in the recently completedWorking Group I Fourth Assessment report ican be accessed through this listing). In fact, since the last report it is also often stated that the science is settled or done and now is the time for action.
In fact there are no predictions by IPCC at all. And there never have been. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios. There are a number of assumptions that go into these emissions scenarios. They are intended to cover a range of possible self consistent “story lines” that then provide decision makers with information about which paths might be more desirable. But they do not consider many things like the recovery of the ozone layer, for instance, or observed trends in forcing agents. There is no estimate, even probabilistically, as to the likelihood of any emissions scenario and no best guess.
Even if there were, the projections are based on model results that provide differences of the future climate relative to that today. None of the models used by IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current observed climate. In particular, the state of the oceans, sea ice, and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models. There is neither an El NiƱo sequence nor any Pacific Decadal Oscillation that replicates the recent past; yet these are critical modes of variability that affect Pacific rim countries and beyond. The Atlantic Multidecadal Oscillation, that may depend on the thermohaline circulation and thus ocean currents in the Atlantic, is not set up to match today’s state, but it is a critical component of the Atlantic hurricanes and it undoubtedly affects forecasts for the next decade from Brazil to Europe. Moreover, the starting climate state in several of the models may depart significantly from the real climate owing to model errors. I postulate that regional climate change is impossible to deal with properly unless the models are initialized.
The current projection method works to the extent it does because it utilizes differences from one time to another and the main model bias and systematic errors are thereby subtracted out. This assumes linearity. It works for global forced variations, but it can not work for many aspects of climate, especially those related to the water cycle. For instance, if the current state is one of drought then it is unlikely to get drier, but unrealistic model states and model biases can easily violate such constraints and project drier conditions. Of course one can initialize a climate model, but a biased model will immediately drift back to the model climate and the predicted trends will then be wrong. Therefore the problem of overcoming this shortcoming, and facing up to initializing climate models means not only obtaining sufficient reliable observations of all aspects of the climate system, but also overcoming model biases. So this is a major challenge.

The IPCC report makes it clear that there is a substantial future commitment to further climate change even if we could stabilize atmospheric concentrations of greenhouse gases. And the commitment is even greater given that the best we can realistically hope for in the near term is to perhaps stabilize emissions, which means increases in concentrations of long-lived greenhouse gases indefinitely into the future. Thus future climate change is guaranteed.
So if the science is settled, then what are we planning for and adapting to? A consensus has emerged that “warming of the climate system is unequivocal” to quote the 2007 IPCC Fourth Assessment Working Group I Summary for Policy Makers (pdf) and the science is convincing that humans are the cause. Hence mitigation of the problem: stopping or slowing greenhouse gas emissions into the atmosphere is essential. The science is clear in this respect.
However, the science is not done because we do not have reliable or regional predictions of climate. But we need them. Indeed it is an imperative! So the science is just beginning. Beginning, that is, to face up to the challenge of building a climate information system that tracks the current climate and the agents of change, that initializes models and makes predictions, and that provides useful climate information on many time scales regionally and tailored to many sectoral needs.
We will adapt to climate change. The question is whether it will be planned or not? How disruptive and how much loss of life will there be because we did not adequately plan for the climate changes that are already occurring?
Kevin Trenberth
Climate Analysis Section, NCAR

The Question


The question is not about predictions vs projections. As Dr Trenberth writes in his closing paragraph: We will adapt to climate change. The question is whether it will be planned or not?

This is the global CO2 emissions from fossil fuel and cement production (not including land use change or deforestation) up to and including 2011 from a 2012 report by the PBL Netherlands Environmental Assessment Agency:

SourceTrends in global co2 emissions 2012 Report, PBL Netherlands Environmental Assessment Agency


Click here for an interactive chart in the Guardian, which you can play with.  It shows CO2 emissions from around the world by country, per GDP, per capita etc.


So while WUWT-ers are arguing over whether or not the IPCC makes predictions or is careful with terminology, the world continues to pour carbon dioxide into the air.  We need to drop emissions, by a lot, if we are to have any chance of limiting global warming to just two degrees.

15 comments:

  1. Well, but that is their aim--to buy time for more emissions and more profits. So, no concern about wasting time.

    ReplyDelete
  2. Hello,

    Trenberth said:
    "....In fact there are no predictions by IPCC at all. And there never have been. The IPCC instead proffers “what if” projections of future climate that correspond to certain emissions scenarios. There are a number of assumptions that go into these emissions scenarios......"

    He said there never has been any prediction made by the IPCC. Now here is the IPCC.

    “Based on current model results, we predict: • under the IPCC Business-as-Usual (Scenario A) emissions of greenhouse gases, a rate of increase of global mean temperature during the next century of about 0 3°C per decade (with an uncertainty range of 0 2°C to 0 5°C per decade), this is greater than that seen over the past 10,000 years This will result in a likely increase in global mean temperature of about 1°C above the present value by 2025 and VC before the end of the next century [...] ”
    ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_spm.pdf

    Forecast/Prediction. When a projection is branded “most likely,” it becomes a forecast or prediction. A forecast is often obtained by using deterministic models—possibly a set of such models—outputs of which can enable some level of confidence to be attached to projections….
    http://www.ipcc.ch/ipccreports/tar/wg2/index.php?idp=125

    ReplyDelete
    Replies
    1. There's really no need to emphasise the points I made in my article, Anonymous:

      The WUWT-ers are having trouble working out the difference between IPCC model projections and model predictions. Perhaps they can think of it this way. IPCC models are used to make projections about climate (surface temperature, precipitation, ice cover etc) for a range of different scenarios. ...The word "prediction" could be used when referring to a particular scenario as part of an "if" statement. For example, IF we were to continue to track on or above RCP8.5 I'd predict we'd face a very challenging future!

      WUWT-ers are avoiding the question.

      The question is not about predictions vs projections. As Dr Trenberth writes in his closing paragraph: We will adapt to climate change. The question is whether it will be planned or not?

      Delete
  3. The IPCC did make a prediction based on model results. It was a prediction derived from model run or runs. No?

    Based on current model results, we predict: • under the IPCC Business-as-Usual (Scenario A) emissions of greenhouse gases, a rate of increase of global mean temperature during the next century of about 0 3°C per decade (with an uncertainty range of 0 2°C to 0 5°C per decade), this is greater than that seen over the past 10,000 years This will result in a likely increase in global mean temperature of about 1°C above the present value by 2025 and VC before the end of the next century [...] ”
    ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_spm.pdf

    ReplyDelete
    Replies
    1. You really don't get the difference, or do you?

      Is it that you don't understand what Dr Trenberth was saying? Because you are basically repeating what he is saying. For a given scenario (eg BAU) you could call it a prediction. But that is very different from a blanket - this is what is going to happen regardless. Any "predictions" are, as you keep writing, conditional on a number of factors. In particular which emissions trajectory we choose for the coming years. Taken together the model runs and individual and aggregate results are projections not predictions. It's only in the context of an "if a scenario pans out" that the word "predict" could be used.

      I see a number of people on WUWT can't or won't accept the difference, so you're not alone.

      Or maybe you just enjoy semantic arguments. I can relate to that :)

      Delete
  4. Please pay close attention to the point of the dispute. Focus on the last part of Trenberth's assertion.

    "In fact there are no predictions by IPCC at all. And there never have been."
    http://blogs.nature.com/climatefeedback/2007/06/predictions_of_climate.html

    This is what was challenged.

    ReplyDelete
    Replies
    1. No, that wasn't what was challenged. That was not the real point to the dispute at all. What it was was a WUWT game of gotcha based on wordplay.

      Dr Trenberth is correct in essence. The IPCC doesn't say the world will xyz. It only makes provisional statements. If abc then xyz. Whether it uses the word "prediction" is irrelevant. If you read the IPCC reports more carefully, you'll not that even if the word "predict" is used, it's used in a conditional context.

      The reason the WUWT-ers are harping on the word is probably because they want to avoid the real issue - as I discussed in my article. Plus they want to continue to say "but you predicted xyz" without referring to provisos, scenarios, uncertainties or anything else that scientists take such pains with in their research.

      It's evasion and games, that's all. Typical WUWT.

      Delete
  5. I am Jimbo so I know what I was challenging.

    "In fact there are no predictions by IPCC at all. And there never have been."

    Trenberth says "there never have been". This is not true, see the link below where I give an example of a prediction and the assertion by the IPCC of when a "projection" becomes a "prediction".


    http://wattsupwiththat.com/2013/08/25/trenberths-ipcc-claim-of-no-predictions-by-ipcc-at-all-refuted-by-ipccs-own-words/#comment-1401817

    ReplyDelete
    Replies
    1. Welcome Jimbo.

      Would you also concede that in the context of what he was discussing Dr Kevin Trenberth was correct as is my interpretation? Or would you say you were simply playing gotcha.

      And would you concede that at WUWT the followers have not yet graduated to considering the question posed by Dr Trenberth at the end of his article?

      And would you concede it will be some years before many are willing to consider his question because it's likely to be some years before a lot of them, perhaps most even, are finally convinced that an ice age is not going to come...any day now...any day now...?

      Delete
  6. wait, why is Watts surprised that Nature employs science journalists? there's significantly more to the journal than the peer-reviewed papers: there's news, editorials, reviews, obits. does he expect professional researchers to write all of those as well?

    ReplyDelete
  7. IPCC
    Forecast/Prediction. When a projection is branded “most likely,” it becomes a forecast or prediction. A forecast is often obtained by using deterministic models—possibly a set of such models—outputs of which can enable some level of confidence to be attached to projections….

    Did you see
    "...IT BECOMES A forecast or PREDICTION..."?

    If the IPCC does not do predictions then why define what constitutes a prediction??? Just answer this question.

    ReplyDelete
    Replies
    1. Maybe so that people understand the difference? Maybe in the hope that they'd think about scenarios before jumping to conclusions about projections for global average surface temperature and other changes to come.

      Didn't work too well for some people, did it :(

      Delete
  8. "Would you also concede that in the context of what he was discussing Dr Kevin Trenberth was correct as is my interpretation? Or would you say you were simply playing gotcha."

    No I do not concede. Trenberth made a clear statement. Now, do you concede that in fact the IPCC has made at least ONE prediction in the past??? Can you say yes or no?

    ReplyDelete
    Replies
    1. Is that you, Jimbo? Or is this another Anonymous.

      Whoever - by your comment you don't understand the climate models that Dr Trenberth was talking about. How they are built and how they are used. And I take it that you don't understand the concept of scenarios either. So there's little chance you'd understand any response I gave.

      For the benefit of anyone else who gazes down the page, I guess you go beyond the surface temperature projections of computer models (which is what Dr Trenberth was talking about) and could call the fact that warming is unequivocal and is caused by humans leads to implied predictions, because we haven't shown much sign of cutting CO2 emissions. So the implied if not stated predictions are that earth will continue to warm, seas will continue to rise, ice will continue to melt and the pH of oceans will continue to fall. But you don't need his climate models to make that prediction. And, barring a few supervolcanoes in rapid succession or an all-out nuclear war, it's a sure bet.

      Delete

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