AMS Seminar Discusses the Sun’s Role in Warming

Earlier this week Alexandra Kougentakis, Fellows Assistant at the Center for American Progress, attended one of the American Meteorological Society‘s seminars discussing the latest in climate science (which are great resources for policymakers, as they tend to take place on Capitol Hill). She has kindly reported on the event below:

One of the favorite, though well-debunked, claims of the global warming skeptics is that the recent warming is due to the recent up tick in solar activity. The current solar cycle has indeed seen higher-than-average sunspots, but what most strengthens skeptics’ argument is the lack of knowledge about what this means. In that light, the American Meteorological Society’s recent seminar, “Solar Radiation, Cosmic Rays and Greenhouse Gases: What’s Driving Global Warming?” was especially illuminating

The core of the skeptics’ argument is to take legitimate scientific fact and distort it to serve a false premise. Solar activity is among the external factors listed by the IPCC whose variation could be a source of radiative forcing, which is the net change in solar ray penetration between the two atmospheric layers closest to the earth. In other words, solar activity is potentially a cause of climate change. The historic correlation between solar activity and climatic shifts seen in the paleoclimate record provides evidence to this effect. Since the 17th century, the record of 11-year cycles of solar irradiance, or brightness, charted through the analysis of tree rings and ice cores makes clear that solar irradiance has increased. A correlation has been observed between solar activity and climate shifts, at least up until the mid-20th century, when the connection became sharply weaker.

One of the strongest arguments against attempts to link solar activity to current warming has to do with inconsistencies in the solar signal.

As climate scientist Dr. Caspar Ammann pointed out at the AMS seminar, the atmosphere is divided into different layers between which the impacts of ozone of pollution vary. While the models to predict the layers’ temperatures are not yet perfect, it is understood that solar irradiance would warm both the troposphere, the layer closest to the earth, and the stratosphere, the next outer layer. The warming that the troposphere is experiencing now is accompanied by a cooling of the stratosphere, which signifies that the current flux in solar irradiance is not a complete explanation for current climate shifts.

Climate experts widely recognize that the sun is a minor player at best in the current warming trend, and this is due in part to the scope of its impact seen in the past. At the AMS seminar, solar physicist Dr. Judith Lean further made the point that it is not realistic to separate anthropogenic and solar effects of warming since they are occurring simultaneously.

There are a lot of different factors affecting climate, some natural, some anthropogenic, and likely some that haven’t been clearly identified yet. The interaction between these factors makes it difficult to establish a linear connection between temperatures and a single variable. Addressing the specific argument of the skeptics, however, the solar-climate connection alone cannot account for the level of warming that has occurred since the mid-20th century.

The major take-home message of the AMS seminar, highlighted by both Dr. Lean and Dr. Ammann, was that both the empirical record and modeling demonstrates that current warming trends are most directly explained by anthropogenic greenhouse gas emissions, more than any other factor. This will probably do little to silence the ranting of global warming skeptics, but it is important to understand that it is only too convenient to blame nature for the problems that we bring upon ourselves.

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18 Responses to AMS Seminar Discusses the Sun’s Role in Warming

  1. JCH says:

    The lack of comments proves beyond all doubt that climate scientists have totally forgotten about the sun. When will those cloistered geeks come to their senses?

  2. Earl Killian says:

    JCH, climatologists don’t ignore the sun; they discuss it quite openly. You can read a draft of James Hansen’s latest paper here and see the discussion of the sun:
    The sun has increased its output over a hundred million years while temperature and CO2 fell. Then CO2 rose and temperature rose. What does that tell you?

  3. Erl Happ says:

    A factor that applies equally across all latitudes and all altitudes can not explain the warming that we see. The warming is partial. It is seen only in the high latitudes of the northern hemisphere.

    To suggest that CO2 could be the cause of this partial warming one must entirely diconnect from logical thought process. This is an act of faith that places one in a place safe from any question or debate.

  4. Nylo says:

    It is clear that you do not pay attention to what people defending the solar influence on climate actually say. They don’t talk as much about the ammount of solar irradiance, which increases with sunspots but the increase is small, as you say. They talk more about the magnetic field associated with that radiation and how it affects the cosmic rays that reach the Earth, because of the interaction with the Earth’s magnetic field. Basically, when there are no sunspots, we have more cosmic rays reaching the oceans, and it is known that they increase low cloud formation, although we don’t yet know to what extent. So low solar activity means more clouds and increased albedo, adding up to the effect of the reduced irradiance.

  5. JCH says:

    Earl, I was kidding. Others aren’t.

  6. Joe says:

    Nylo: The experts utterly dismissed cosmic rays. They are like a million times weaker than the sun’s radiation. Cosmic rays have been debunked elsewhere at length.

  7. Ed Davies says:

    “Since the 17th century, the record of 11-year cycles of solar irradiance, or brightness, charted through the analysis of tree rings and ice cores makes clear that solar irradiance has increased.”

    Surely the solar cycles since the 17th century have been recorded by direct observation (sunspot counting). Any connection between such proxy data as tree rings and ice cores and solar irradiance is a bit more indirect and open to interpretation.

  8. Fran Manns says:

    Cosmic radiation, far from being ‘utterly dismissed ” or debunked, is being studied by experiment by scientists at the Danish National Space Center. Are there any CO2 greenhouse gas studies, other than qualitative thought experiments by the AGW side since 1890s? See their web site. Read “The Chilling Stars”.

  9. Joe says:

    Fran — Debunked as in

    The IPCC details hundreds of studies on the CO2/GHG side. If you want to be taken seriously, you’ll have to much, much better.

  10. Nylo says:

    Joe, you continue to miss the point. It’s not about any “warming power” of the cosmic rays themselves. It’s the fact that they influence cloud formation and that increases the albedo, which causes more of the normal Sun radiation not to reach the surface and be reflected back to the space. The cosmic rays affect as if they were a catalyzer of other reactions that result in a cooling effect. They are not conferring any energy to the system. Their action is more subtle.

  11. Joe says:

    Nylo — You didn’t read the link. Yes, “Their action is more subtle” — so subtle that there is in fact no supporting data.

  12. David B. Benson says:

    Nylo — No change in cosmic ray flux during the last fifty years. Global warming during the last fifty years. Something else must be causing the change. Hmmm. Measured increase in CO2 during the last fifty years. !! (Moment of Zen enlightenment.)

  13. Nylo says:

    David, this is about spreading science, not lies. Cosmic ray flux has indeed changed. Look at the article “Influence of Cosmic Rays on Earth’s Climate”, by Henrik Svensmark in 1998. I found it in Google’s cache. I provide the link:

    I will copy below 3 paragraphs that concentrate on this issue:

    […] Clouds reflect more energy than they trap and this leads to a cooling in the range of 17 to 35 Wm-2 [21-23]. It is not easy to estimate the net change in radiative forcing from a solar modulation of the cloud cover. The main problem is that it is not known which part of the cloud volume is affected. This is important because different cloud types have different radiative properties. Although the net effect of clouds is to cool the planet, high thin clouds tend to warm the Earth’s surface, and therefore one could imagine that an increase in cosmic ray flux could lead to a warming. However, high thin clouds which tend to warm the Earth’s surface occur in association with high thick cooling clouds, and together the two cloud types tend to mitigate their effect on the energy balance [24]. The results of Fig. 3b seem to suggest that an increase in cloud cover results in a cooling, which again suggest that a larger part of the cloud volume is affected.

    From Fig. 3 it is seen that the temperature in the period 1970-1990 rose by approximately 0.3’C. It is possible to compare the variation in cosmic ray flux (assuming it is directly correlated with cloud cover) and this temperature change via some simple assumptions. From cloud satellite observations and numerical cloud modeling it is found that a 1% change in the total composition of Earth’s cloud cover corresponds to 0.5 W/m2 change in net radiative forcing [25]. From Svensmark and Friis-Christensen [7] it is known that from 1987 to 1990 global cloudiness changed approximately 3.0% which can be estimated to be 1.50 W/mZ [7]. In the same period cosmic rays from the ion chamber changed 3.5% as seen in Fig. 2. We can now calculate the approximate radiative forcing by noting that the mean 11 year average increase of cosmic rays in Fig. 3 from 1975 to 1989 is 1.2%, which then corresponds to a possible 0.5 W/m2 change in cloud forcing. This is a fairly large forcing, about 4 times the estimated change in solar irradiance. The resulting temperature change is difficult to estimate exactly. Studies obtained from a general circulation model gave a sensitivity (0.7 to I’C/Wm-2 for DS =0.25%, where S is the solar constant) [26]. The direct influence of changes in solar irradiance is estimated to be only 0.1’C [6]. The cloud forcing, however, gives for the above sensitivity, 0.3-0.5’C, and has therefore the potential of explaining nearly all of the temperature changes in the period studied.

    The solar cycle length has been shown to be an important parameter due to its close connection with temperature variations of the Earth. This parameter is determined empirically and it has not been straightforward to interpret. The present work gives a hint on why it is relevant to Earth’s climate. The physical interpretation is based on the close agreement between variations in solar cycle length, GCR flux, and temperature as seen in Fig. 3. The solar cycle length is therefore a measure of the processes occurring within the sun of unknown dynamical origin which manifest themselves in the solar activity within the heliosphere that modulates the GCR, averaged over the solar cycle.

    One can disagree with the conclussions he obtains, but not with the data. There has been a change in the solar flux, indeed. a 3,5% decrease. And there has been a cloudiness reduction, indeed. A 1% decrease. This seems to indicate that cloud formation is related to cosmic rays, to some extent. Further data found in the article supports this. And this has happened during 20 years of increased warming.

    I disagree with him anyway because I don’t think that the GCR explains all the heating. GH effect is real, it exists. Only its effect on temperature is not as overwhelmingly important as the alarmists try to persuade us it is.

  14. Nylo says:

    Error correction: the 3,5% variation is in cosmic rays and is in the period of only 1987 to 1990. The overall variation of cosmic rays in 11 years of high solar flux is only 1,2%, but is enough to explain the warming trend in that period of time.

    Here you have another interesting article about relationship between cosmic rays and temperature. The graphs are very clarifying…

  15. Nylo says:

    One more interesting article about this phenomenom in the Wikipedia:

  16. David B. Benson says:

    Nylo — Go find the original data on cosmic ray flux. Do the statistics (properly) on that data. I stand by my statement.

  17. Nylo says:

    David, you can stand by what you want to stand by. You can even stand by the Earth being flat. That won’t make it true. I already gave you the data. If you think that it is not the true data, despite having been published in peer-reviewed scientific journals and being aproximately the same for different ways of measuring cosmic ray flux (the Neutron Monitor in Climax, Colorado, since 1953, or ionization chambers since 1937), it is YOU who has to provide with new data and prove that it is more… correct, so to say, to prove your point.

  18. Francis Manns says:

    People find what they look for and the minute a scientist believes his own hypothesis, he’s a dead duck as a scientist.
    My hypothesis is climate change is not man-made.
    The hypothesis runs:
    It’s not solar irradiance alone.
    It’s not sunspots alone.
    It’s not CO2 above 18 C.
    it’s not water vapour alone.
    It’s not cosmic radiation alone.’
    But it may be cosmic and solar radiation modulated by solar magnetic activity subtly changing the cloud albedo of Earth.

    Beware the unintended consequences of sequestering plant food during the famine.