9 Responses to Study: Water-vapor feedback is “strong and positive,” so we face “warming of several degrees Celsius”
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 newClimate 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:
- The defrosting of the permafrost
- The drying of the Northern peatlands (bogs, moors, and mires).
- The destruction of the tropical wetlands
- Decelerating growth in tropical forest trees — thanks to accelerating carbon dioxide
- Wildfires and Climate-Driven forest destruction by pests
- The desertification-global warming feedback
- The saturation of the ocean carbon sink
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.