Climate change feedback effects

Starting with an index card full of items to include, I tried to make a map of basic feedbacks relating to climate change. I got this far, then decided that it probably cannot be done in two dimensions, except perhaps on a really massive sheet of paper:

Selected climate feedbacks

Note: a chemical formula in [square brackets] indicates the concentration of that substance.

Consider, for instance, a single pathway of effects. Agriculture uses fossil fuels, which produce CO2. The CO2 raises global temperature, affecting global cloud cover in an uncertain way. The cloud cover affects temperature, by reflecting more or less solar radiation back into space. It also affects the rate of forest and plankton growth (as does the original increase in CO2).

All told, you need to account for phenomena in the following domains: atmosphere (gas concentrations, cloud effects), hydrosphere (ocean density, temperature, currents), cryosphere (ice and glacier levels, permafrost), and biosphere (plant growth, forest fires). Add to that feedbacks within human behaviours (agriculture and forest burning, for instance) and feedbacks between anthropogenic and non-anthropogenic sources of climate change, such as volcanic eruptions (lithosphere) and changes in orbits and solar output. Doubtless, I have overlooked and forgotten many relevant effects, also.

My hat goes off to the producers of general climate models (GCMs) that have started to incorporate the most important of the linkages shown above. These complex dynamic systems are tricky things, not easily dealt with through the general tendency in science to break questiond down and understand them bit-by-bit.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

16 thoughts on “Climate change feedback effects”

  1. Surely no existing climatic models actually include all of those things.

    Of course, unless there are big surprises in how some of those relationships change as greenhouse gas levels do, we may not need to model the rest.

  2. You also left out the whole ozone system.

    You could add another purple box for CFCs and HCFCs, a blue box for stratospheric ozone, and connections between CFC concentration and ozone levels, ozone levels and plant growth, and CFC concentration and temperature.

  3. Because of the harmful effects of extra UV on crops, “Stratospheric ozone” should be linked to “Agriculture” as well. There are surely dozens if not hundreds more boxes and links. For instance:

    Oceanic acidity

    [CO2] to “Ocean pH”
    “Ocean pH” to “Plankton” (two way?)

    Air travel

    “Air travel” to “Jet contrails” and [CO2]
    “Jet contrails” to “Cloud cover”

    Heating and air conditioning

    Link “Temperature” back to “Fossil fuel use”

  4. Adding [SO2] would make things more complicated still. That would link to plant growth (land and sea), fossil fuel use, and ocean pH.

  5. “The Earth’s climate is so irreducibly complicated that we will never grasp it completely, in the way that we might grasp a law of physics. These uncertainties infect the relationship between science and policy-making.”


  6. An Abrupt Climate Change Scenario and Its Implications for United States National Security

    PETER SCHWARTZ & DOUG RANDALL / GBN Global Business Network October 2003

    Imagining the Unthinkable

    The purpose of this report is to imagine the unthinkable – to push the boundaries of current research on climate change so we may better understand the potential implications on United States national security.

    We have interviewed leading climate change scientists, conducted additional research, and reviewed several iterations of the scenario with these experts. The scientists support this project, but caution that the scenario depicted is extreme in two fundamental ways. First, they suggest the occurrences we outline would most likely happen in a few regions, rather than on globally. Second, they say the magnitude of the event may be considerably smaller.

    We have created a climate change scenario that although not the most likely, is plausible, and would challenge United States national security in ways that should be considered immediately.

  7. “Charney was seeking the equilibrium global warming, the warming after the atmosphere and ocean have come to a new final temperature in response to increased carbon dioxide. The immediate effect of doubling carbon dioxide, if everything else were fixed, would be a decrease of about 4 watts (per square metre) in the heat radiation from Earth to space. This is simply physics… The added carbon dioxide increases the opacity (opaqueness) of the atmosphere for heat radiation, so radiation to space arises from a higher level, where it is colder, thus reducing emission to space.

    Any physicist worth his salt can immediately tell you the answer to Charney’s problem if everything except temperature is fixed… We can use Planck’s law to calculate how much Earth must warm up to radiate 4 more watts and restore the planet’s energy balance. The answer we find is 1.2 degrees Celsius. So the climate sensitivity in this simple case of Planck radiation is 0.3 degrees Celsius per watt of climate forcing.

    This simple Planck’s law climate sensitivity, 0.3 degrees Celsius per watt of climate forcing, is called the no-feedback climate sensitivity. Feedbacks occur in response to variations in temperature and can cause further global temperature change, either magnifying or diminishing the no-feedback, or blackbody, response. Feedbacks are the guts of the climate problem. Forcings drive climate change. Feedbacks determine the magnitude of climate change.

    Hansen, James. Storms of My Grandchildren. p.42 (hardcover)

  8. In addition to its role in protecting the Earth from the Sun’s harmful ultraviolet rays, ozone is also a greenhouse gas. The ozone layer is part of a vast chemical network, and changes in environmental conditions, such as changes in temperature or the atmospheric circulation, result in changes in ozone abundance. This process is known as an atmospheric chemical feedback.

    Using a comprehensive atmosphere-ocean chemistry-climate model, the Cambridge team, working with researchers from the University of East Anglia, the National Centre for Atmospheric Science, the Met Office and the University of Reading, compared ozone at pre-industrial levels with how it evolves in response to a quadrupling of CO2 in the atmosphere, which is a standard climate change experiment.

    What they discovered is a reduction in global surface warming of approximately 20% — equating to 1° Celsius — when compared with most models after 75 years. This difference is due to ozone changes in the lower stratosphere in the tropics, which are mainly caused by changes in the atmospheric circulation under climate change.

    “This research has shown that ozone feedback can play a major role in global warming and that it should be included consistently in climate models,” said Nowack. “These models are incredibly complex, just as the Earth is, and there are an almost infinite number of different processes which we could include. Many different processes have to be simplified in order to make them run effectively within the model, but what this research shows is that ozone feedback plays a major role in climate change, and therefore should be included in models in order to make them as accurate as we can make them. However, this particular feedback is especially complex since it depends on many other climate processes that models still simulate differently. Therefore, the best option to represent this feedback consistently might be to calculate ozone changes in every model, in spite of the high computational costs of such a procedure.

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