Wild et al 2001 on Downward Longwave Radiation

Wild et al. [2001], a blue-chip study, shows that the downward longwave radiation in cold, dry climates is dramatically under-estimated in the GCMs used in IPCC TAR, as shown in the following excerpt from their Figure 4 (from one of the best GCMs). The bias is systemic.

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FIG. 4. Annual cycles of model-calculated and observed DLR (W m22) at some of the most reliable high-latitude sites, midlatitude sites, and low-latitude sites (see Table 1 for more information on these sites): model calculations by ECHAM3 (dotted) and ECHAM4 (dashed), and observed (solid). MARTIN WILD, ATSUMU OHMURA, AND HANS GILGEN, JEAN-JACQUES MORCRETTE, ANTHONY SLINGO, 2001, Evaluation of Downward Longwave Radiation in General Circulation Models, Journal of Climate 14.

Abstract: The longwave radiation emitted by the atmosphere toward the surface [downward longwave radiation (DLR)] is a crucial factor in the exchange of energy between the earth surface and the atmosphere and in the context of radiation-induced climate change. Accurate modeling of this quantity is therefore a fundamental prerequisite for a reliable simulation and projection of the surface climate in coupled general circulation models (GCM). DLR climatologies calculated in a number of GCMs and in a model in assimilation mode (reanalysis) are analyzed using newly available data from 45 worldwide distributed observation sites of the Global Energy Balance Archive (GEBA) and the Baseline Surface Radiation Network (BSRN). It is shown that substantial biases are present in the GCM-calculated DLR climatologies, with the GCMs typically underestimating the DLR (estimated here to be approximately 344 W m22 globally). The biases are, however, not geographically homogeneous, but depend systematically on the prevailing atmospheric conditions. The DLR is significantly underestimated particularly at observation sites with cold and dry climates and thus little DLR emission. This underestimation gradually diminishes toward sites with more moderate climates; at sites with warm or humid atmospheric conditions and strong DLR emission, the GCM-calculated DLR is in better agreement with the observations or even overestimates them. This is equivalent to creating an excessively strong meridional gradient of DLR in the GCMs.The very same tendencies are independently found in stand-alone calculations with the GCM radiation codes in isolation, using observed atmospheric profiles of temperature and humidity for cloud-free conditions as input to the radiation schemes. A significant underestimation of DLR is calculated by the radiation schemes when driven with clear-sky atmospheric profiles of temperature and humidity representative for cold and dry climates, whereas the DLR is no longer underestimated by the radiation schemes with prescribed clear-sky profiles representative for a hot and humid atmosphere. This suggests that the biases in the GCM-calculated DLR climatologies are predominantly induced by problems in the simulated emission of the cloud-free atmosphere. The same biases are also found in the DLR fluxes calculated by the European Centre for Medium-Range Weather Forecasts (ECMWF) model in assimilation mode (reanalysis), in which the biases in the atmospheric thermal and humidity structure are minimized. This gives further support that the biases in the DLR are not primarily due to errors in the model-predicted atmospheric temperature and humidity profiles that enter the radiative transfer calculations, but rather are due to the radiation schemes themselves. A particular problem in these schemes is the accurate simulation of the thermal emission from the cold, dry, cloud-free atmosphere.


  1. John A
    Posted Apr 13, 2005 at 3:42 PM | Permalink

    As a bystander comment, shouldn’t the GCMs be most accurate in cold, dry, cloudless atmospheres and less accurate with the issues of cloudiness and evaporation?

    the biases in the DLR are not primarily due to errors in the model-predicted atmospheric temperature and humidity profiles that enter the radiative transfer calculations, but rather are due to the radiation schemes themselves.

    Does this mean that the expectations of the programmers in modelling radiative forcing are causing this problem?

  2. Douglas Hoyt
    Posted Apr 13, 2005 at 5:57 PM | Permalink

    Perhaps the errors are due to incorrect humidity profiles as discussed here:


    The humidity above 10 km is underestimated substantially. Using the incorrect low humidity values would lead to an underestimation of the LW radiation in the GCMs and an overestimation of the SW radiation at the surface in the GCMs. Both of these biases have been observed in the models.

    Perhaps even more alarming for the modelers is that it means the water vapor feedback cannot be very effective since the upper atmosphere is already saturated with water vapor. That would mean that about 1.5 C of the warming in typical models is erroneous.

  3. Greg F
    Posted Apr 14, 2005 at 4:24 AM | Permalink

    This paper to be published is perhaps somewhat related.

    Since the explanation of Pinatubo by the computer models was wrong in regard to the response time and the negative feedback, Douglass asks, “Are the computer models right when they consider the change to the climate caused by carbon dioxide?”

  4. Michael Ballantine
    Posted Apr 14, 2005 at 7:59 AM | Permalink

    Good posting Greg. The paper certainly sounds good. Actual observations over a relatively short time using a consistent set of instruments that only need short term stability instead of long term stability and correlation to other esoteric stuff.
    Sounds like indisputable proof that the current models need a lot of work and are useless in their present condition for any kind of useful predictions.
    A single, reproducable, observable fact that does not fit a theory/model is all it takes to disprove the theory/model. It is really too bad that so many prominent climate “scientists” have forgotten/ignored this simple axiom of real science.
    Let’s keep ’em coming people.

  5. Chas
    Posted Apr 20, 2005 at 12:46 PM | Permalink

    Here’s a link to the Douglass & Knox paper that Greg pointed out:

  6. John A.
    Posted Apr 20, 2005 at 1:58 PM | Permalink

    Re: #5


  7. Greg F
    Posted Apr 22, 2005 at 3:09 PM | Permalink

    Wow … thanks a lot Chas. I just read through it quickly and this, I believe, will prove to be a very important paper. They used a volcanic eruption to measure impulse response of the atmosphere. Anybody who has any experience with signal processing (DSP) will understand the implications of this paper. (The U of R has a pretty good EE department … hmmmm).

  8. Michael Mayson
    Posted Apr 24, 2005 at 11:34 PM | Permalink

    Here is another observation – changes in the earth’s albedo – that climate models do not take into account.


    If they stand up to scrutiny, these observations will also have major implications.

  9. Chas
    Posted Apr 25, 2005 at 3:42 AM | Permalink

    Here’s a link to the earth-albedo paper that Micheal Mayson pointed out:

    I’ve just tried a(Beta)Google search page http://scholar.google.com
    It looks as if it might be pretty good at tracking down copies of papers.

  10. Michael Mayson
    Posted Apr 26, 2005 at 2:21 AM | Permalink

    Thanks Chas – I got to the Science site and the paper ( without having to log in) from here http://www.bbso.njit.edu/~epb/papers.html. There are some other interesting papers as well.

  11. Chas
    Posted Apr 26, 2005 at 11:48 AM | Permalink

    Michael it is curious how sometimes one seems to get to the full paper via a link to a journal,though the bbso link didnt do it for me this time. (BTW the link needs its last full stop removing).
    Many thanks for pointing to the paper! It does look to be exceptionally important.
    -There is a second (public)collection of interesting .pdfs on the site at: http://solar.njit.edu/publications.htm
    incl a recent cloud:cosmic ray study 🙂

  12. Michael Mayson
    Posted Apr 26, 2005 at 2:53 PM | Permalink

    Chas – amongst those papers at http://solar.njit.edu/publications.htm is this one

    “The Earthshine Project: Update on Photometric and Spectroscopic Measurements”

    whihc comments:

    “Our simulations suggest a surface average
    forcing at the top of the atmosphere, coming only from
    changes in the albedo from 1994/1995 to 1999/2001, of
    2.7-1.4 W/m2 (Palle et al., 2003), while observations
    give 7.5-2.4 W/m2. The Intergovernmental Panel on
    Climate Change (IPCC, 1995) argues for a comparably
    sized 2.4 W/m2 increase in forcing, which is attributed to
    greenhouse gas forcing since 1850.
    Still, whether the Earth’s reflectance varies with the
    solar cycle is a matter of controversy, but regardless of
    its origin, if it were real, such a change in the net sunlight
    reaching the Earth would be very significant for the
    climate system.”


    “Traditionally the Earth’s albedo has been considered
    as a roughly invariant parameter in global circulation
    models and climate studies. With the earthshine project,
    we have shown how, on the contrary, the Earth’s albedo
    is quite a variable parameter for which a detailed study
    of its seasonality, long-term variability and climate implications
    need to be carefully undertaken, if we are to
    fully understand the present changes in the Earth’s climate.”

  13. Chas
    Posted Apr 27, 2005 at 12:30 AM | Permalink

    !!! Micheal, I dont know if you post at RC, but it would be interesting to read what Gavin makes of these two. The ‘Water Vapour’ commenting looks open.
    If your post is rejected/deleted then they are probably very significant 😉

  14. Michael Mayson
    Posted Apr 27, 2005 at 5:28 AM | Permalink

    Chas – I did post this at Real Climate but they appear to not know much about it – which I find disturbing – see http://www.realclimate.org/index.php?p=119#comments.

  15. Chas
    Posted Apr 27, 2005 at 3:25 PM | Permalink

    Nice post- Though sadly Rasmus seems to have confused the nightly values of Fig.2 with the annual means of Fig.3
    They didnt seem to have come across De Laat and Maurellis’s industrial CO2:temperature trends work either.

  16. Hans Erren
    Posted Feb 16, 2007 at 6:54 AM | Permalink

    I don’t know how this is incorporated in the models:

    A parametrisation of ocean albedo which is depending on wind speed.

    Jin, Z., T. Charlock, W. Smith Jr., and K. Rutledge, 2004: A parameterization of ocean surface albedo. Geophys. Res. Let., 31, L22301, doi:10.1029/2004GL021180.


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