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Study: Water-vapor feedback is “strong and positive,” so we face “warming of several degrees Celsius”

By Joe Romm  

"Study: Water-vapor feedback is “strong and positive,” so we face “warming of several degrees Celsius”"


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A new study in Geophysical Research Letters (subs. req’d), “Water-vapor climate feedback inferred from climate fluctuations, 2003–2008” analyzed recent variations in surface temperature and “the response of tropospheric water vapor to these variations.” They concluded that the “water-vapor feedback implied by these observations is strongly positive” and “similar to that simulated by climate models.” The analysis concludes:

The existence of a strong and positive water-vapor feedback means that projected business-as-usual greenhouse-gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius. The only way that will not happen is if a strong, negative, and currently unknown feedback is discovered somewhere in our climate system.

A “warming of several degrees Celsius” = the end of life as we know it (see “Is 450 ppm politically possible? Part 0: The alternative is humanity’s self-destruction“).

While some denyers/delayers/inactivists, like MIT’s Richard Lindzen, have argued that negative feedbacks dominate the climate — all of the evidence points to amplifying feedbacks dominating (except the one negative feedback that the deniers fiercely fight, discussed below).

That was a key point of my post “Are Scientists Underestimating Climate Change, Part 1“: In the real world, key climate change impacts — sea ice loss, ice sheet melting, desertification, and sea level rise — all are either near the top or actually in excess of their values as predicted by the IPCC’s climate models. For a more recent detailed discussion of accelerating climate impacts and what that portends for the future on our current emissions path, see the new WWF report Climate Change: faster, stronger, sooner.”

The major climate models are missing key amplifying feedbacks, some of which were discussed in “Are Scientists Underestimating Climate Change, Part II.” These feedbacks include:

And this all supports the analysis that the climate is much more sensitive to changes in greenhouse gas emissions and other “forcings” than the IPCC models have been saying and that a doubling of atmospheric concentrations of carbon dioxide from preindustrial levels to 550 ppm will ultimately warm the planet far more than 3°C, as NASA’s James Hansen argues (see ‘Long-term’ climate sensitivity of 6°C for doubled CO2).

A number of major studies looking at paleoclimate data come to the same conclusion. Here are three:

Scientists analyzed data from a major expedition to retrieve deep marine sediments beneath the Arctic to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” This 2006 study, published in Nature (subs. req’d), found Artic temperatures almost beyond imagination–above 23°C (74°F)–temperatures more than 18°F warmer than current climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

A second study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the Middle Ages. This 2006 study found that the effect of amplifying feedbacks in the climate system–where global warming boosts atmospheric CO2 levels–”will promote warming by an extra 15 percent to 78 percent on a century-scale” compared to typical estimates by the U.N.’s Intergovernmental Panel on Climate Change. The study notes these results may even be “conservative” because they ignore other greenhouse gases such as methane, whose levels will likely be boosted as temperatures warm.

The third study, published in Geophysical Research Letters (subs. req’d), looked at temperature and atmospheric changes during the past 400,000 years. This study found evidence for significant increases in both CO2 and methane (CH4) levels as temperatures rise. The conclusion: If our current climate models correctly accounted for such “missing feedbacks,” then “we would be predicting a significantly greater increase in global warming than is currently forecast over the next century and beyond”–as much as 1.5°C warmer this century alone.

Yes, natural negative feedbacks exist that would “eventually” absorb any excess carbon dioxide, but as one of the authors of a 2008 Nature Geosciences article explained, “not for hundreds of thousands of years” (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks“).

Truly only one negative feedback in the planet’s overall carbon cycle can act with sufficient speed and strength to avert catastrophic climate impacts: The dominant carbon-based life form on this planet will have to respond to the already painfully clear impacts of our carbon emissions by slashing those emissions sharply and eventually running the planet on carbon-negative power.

The time for this negative feedback is now.


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9 Responses to Study: Water-vapor feedback is “strong and positive,” so we face “warming of several degrees Celsius”

  1. john says:

    The WWF study left out one of the more serious feedbacks — the dying of the boreal and alpine forests.

    Boreal forests are the largest terrestial carbon sink, and they are shifting form sink to source as they are assaulted by pine bark beetles.

    There are other, less well known but significant feedbacks. For example as ice shrinks populations of krill are plummeting. Aside from being a key species in the food chain, their feeding habits also remove substantial amounts of carbon from the atmosphere. Less Krill means more carbon staying in the atmosphere.

    The plain truth is, there are a lot of “minor” feedbacks such as this that cumulatively explain why our models have failed to keep up with reality.

  2. paulm says:

    This is the reality…not nice.

    Australia’s Stern review warns of runaway global warming
    “Carbon emissions are rising so fast that the world has no chance of hitting climate targets, says Australian economist”

    The only way that we can limit the rise to 2C is if we have a deep global depression now and throw everything in to coming out of it with zero emission technology!

    Even at 2C we might have gone past major thresholds so its still fingers crossed.

  3. paulm says:

    Here is more reality….were probably fried!

    Looking at CO2 levels (forget temp) – Pretty much every relative CO2 rise in history as resulted in mass extinction. See..


    Now look at the recent levels of CO2….

  4. Hank Roberts says:

    Paulm, pointer to graphics that also state the data sources, which may be useful in explaining this stuff:

  5. A. McIntire says:

    Over the last 30 years or so, we’ve warmed at a rate of 1.28 C per century.


    Hansen’s estimates of 3 to 6 C are a hysterical overreaction.

    Incidentally, desertification would be a net negative, not positive, feedback.
    Compare temperatures in Florida with those in the desert southwest or North Africa at comparable latitudes. True, the DAYTIME temperatures are warmer in the desert, but at night those desert temperatures drop a LOT. The AVERAGE diurnal temperature is warmer in non-desert Florida-

    [JR: CO2 levels are rising, and that's why The rate of temperature rise accelerates. But what is the point in arguing with somebody who so confused about desertification. If we lose soil carbon over one third of the land, that is an unmitigated climate catastrophe.]

  6. A. McIntire says:

    The effect of CO2 is logarithmic. The rate of increase has been roughly constant over the last 30 years- that would imply the effect of CO2 on temperature would be going down.

    [JR: Factually untrue. Try reading this blog.]

    The Clausius Clayperon equation would inply that WATER VAPOR would increase almost exponential, leading to a roughly linear increase in temperature, but NOTHING would indicate an acceleration in temperature change. Incidentally, there has been no measured increase in water vapor, which I’ll admit is pretty diffiuclt to measure accurately. In fact, measured temperatures have gone down worldwide since 2002, probably because the PDO has gone into a negative phase. When the temperature increase was detected in the late 1970s, the PDO had just shifted from a negative to a positive phase. The resulting natural increase in temperature was assumed to be part of global warming. As a result, the rate of temperatue increase caused by manmade global warming was wildly overestimated. Another problem with Hansen’s model is the assumed positive feedback caused by melting glaciers. At the end of the last ice age a lot more ice was exposed directly to the sun. Now that the icecaps are restricted to the poles, the feedback from melting ice would be a heck of a lot less than the feedback 10,000 years ago.

    [JR: Try reading his paper or this blog -- many other amplifying feedbacks exist.]