2 Key Climate Terms to Know

Lisa MooreThis post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

Scientists use some technical terms in discussing climate change that can cause confusion. Two that are especially useful to know are "forcing" and "feedback".

You’ll hear these terms a lot in discussions of how human activity impacts climate – and especially when the topic turns to the melting Arctic. If you know what they mean, you’ll have a much better understanding of the dynamics behind climate change.

"Forcing" and "feedback" both refer to effects on the Earth’s climate system. Climate changes when there’s a change in climate system’s energy balance – the amount of energy absorbed from the Sun, versus the amount of energy radiated back into space from Earth’s lower atmosphere and surface. A process that changes this energy balance – and thus the climate – is called a "climate forcing".

Many things can cause climate forcing. Some, like shifts in the Earth’s orbit around the Sun or volcanic eruptions, are natural events. Others, like increased concentrations of greenhouse gases in the atmosphere, are caused by human activities. Climate change caused by human activity is called "anthropogenic forcing".

A climate feedback is an indirect (or "secondary") change within the climate system that occurs in response to a forcing. For example, warmer air can hold more water vapor, and water vapor can trap more solar energy in the atmosphere, augmenting the warming effect. This is a positive climate feedback because the secondary effect is in the same direction as the primary effect – both are warming.

Another example of a positive climate feedback occurs with sea ice, which is why you hear the term "feedback" in discussions of Arctic warming. As temperatures rise, sea ice melts and exposes open water. Water is darker than ice so it reflects less sunlight and absorbs more energy. This augments the warming effect, leading to more sea ice melting, and so on in a loop.

Climate feedbacks also can be negative, reducing the initial effect rather than augmenting it. For example, increased water vapor in the atmosphere due to warming can lead to more cloud formation. Thick low clouds can block sunlight from reaching the Earth by reflecting it back into space. This creates a cooling effect – a negative climate feedback.

Positive climate feedbacks are dangerous because they can accelerate climate change towards tipping points, critical thresholds at which a small change qualitatively alters the state of some Earth system. For example, the Greenland Ice Sheet could start a slow but irreversible meltdown if global temperature rises above a tipping point, which scientists warn could be just 2°F above today’s temperature.

Tipping points also can trigger climate feedbacks. For example, if the Earth warms enough to melt permafrost (a tipping point for the Arctic region), the melted ground can release greenhouse gases that, in turn, accelerate warming. In fact, studies show that methane emissions are increasing from areas of thawing permafrost in Siberia.

Sound scary? It is. This is why many scientists are pushing hard for legislation to cap greenhouse gas emissions.

This entry was posted in Basic Science of Global Warming. Bookmark the permalink. Both comments and trackbacks are currently closed.


  1. Posted February 29, 2008 at 7:26 pm | Permalink

    A very informative and enlightening article. Thank you very much. We are a big fan of your site.

  2. fred1
    Posted March 3, 2008 at 8:25 pm | Permalink

    So historically, it has been 2 degrees F warmer than it is currently. when it was warmer than now by more than 2 degrees F did the Greenland ice sheet have a “slow but irreversible meltdown?” the same can be said about the Siberian permafrost….

    i am sure there have been times in the last 500,000 years where global temps were warmer than they are today? and similar events (Greenland ice cap meltdown, Siberian permafrost methane emissions increasing).

    you are basing your concerns about these future events since they have happened in the past correct?

    so, can you point to links that show in the past when temps were warmer we had the GReenland ice pack meltdown and dangerous levels of methane released from the Siberian permafrost? how much warmer was it and how long ago did these events occur? can you back up your above statements with historical facts and events?

  3. earthscientist
    Posted March 11, 2008 at 7:05 pm | Permalink

    Ms. Lisa , Please allow yourself to task grid science facts before you support only one science team(Hansen,et al) with facts that they cannot properly support in the presence of any grid scientist.

    I partially explained the grid science process in a comment in 4-11 here about his book.

    All scientists have a great responsibility to do their own work and your support of the earths eco-system is very commendable to us.

    We do ask though that you seek further answers as to the earths processes before you sign in to the GHG model of continued warming and the complete destruction of our earth based on the assumption of carbon being the culprit and the process escalating.

    As I have stated,it is a periodical process and does have an ending date and magma temp and weather processes will return to stability,acceptable to those concerned.

    Actually the facts are that we will have a much cooler period for a few years because as the energy componentry abates,it pulls some of our grid fields energy to it,just as comets pull energy to them. So be prepared for that eventuality.

    We have oxygenation pouring in constantly from our grid field and methane will fall to ground as it always has.

    Also as I have stated before in other formats,jet fuel pouring into our atmosphere creates most of the problems for our ozone shield as well of course the halogens.

    I continually assert that the climate meetings ,if those scientist types were serious about the gases in our atmosphere would hold video meetings instead of assisting in the pouring of the carbon components all the way to their favorite vacation / meeting spot.

    We have designed a complete train system and call for aircraft to only be used for over ocean flights to assist the oxygenation of the planet,which will never be fixed no matter how many wind plants or solar or the foolish carbon sequestration schemes as long as science folks do not support the remediation process with proper perspective as to the real issues of our eco-system.

    We have also designed a complete trash remediation system so our aquifers will not be further destroyed.

    There are plastic to oil processes to turn our plastic waste back to oil and we use that in our trash model along with a long list of other processes that always take things into perspective so as not to task against business or labor.

    The list goes on and on of the new processes grid scientists wish to remediate our eco system with……..And it puts everyone to work.

  4. fred1
    Posted March 17, 2008 at 9:41 pm | Permalink


    you never answered my question….So historically, when it has been 2 degrees F warmer than it is currently, did the Greenland ice sheet have a “slow but irreversible meltdown?”

    Can you show me historical data that proves that the Grrenland ice sheet meltdown has ocurred in this past when temps were 2 degrees warmer than now?

  5. Posted March 18, 2008 at 9:49 am | Permalink

    Check out IPCC Chapters 6, 10 and 19.

    For example, from Chapter 19, starting at the bottom of page 793:
    “paleoclimateic evidence suggests that Greenland and possibly the WAIS contributed to a sea-level rise of 4-6 meters during the last interglacial, when polar temperatures were 3-5 degrees C warmer, and the global mean was not notably warmer, than at present. Accordingly, there is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the WAIS, would occur over a period of time ranging from centuries to millennia for a global average temperature increase of 1-4 degrees Celsius (relative to 1990-2000), causing a contribution to sea-level rise of 4-6 meters or more.”

    There are references to other studies and sections of the IPCC report that give more detail.