Sentences with phrase «on water vapour feedbacks»

TAR, ¶ 7.2.1.3 Summary on water vapour feedbacks, pp. 426 - 7.

Skeptical Science has covered cloud feedback here, and as an interesting aside, amongst many papers on this subject, Dessler has a new paper on water vapour feedbacks in the Journal of Climate.

The tropical tropospheric hot spot prediction is not based on water vapour feedback to warming, and it is especially not unique to warming due to any other GHG forcing.

Not exact matches

Remember that direct greenhouse effect from CO2 is quite small; the predictions rely on positive feedback from other effects (particularly water vapour feedbacks, a far more significant greenhouse gas) to cause substantial warming.

Both cause temperature change so both will play a role in any future water vapour feedback process that is dependent on temperature.

The argument that water vapour is a feedback, rather than a forcing, seems to rest on the fact that it is condensable within a few days, rather than 100's of years like CO2.

On temperature dependence, water vapour feedback, once in place, will be self - sustaining (it will require a greater forcing to reverse compared with the initial forcing it started with)?

Note also that going back to the ice ages, the glacial - interglacial temperature swing can not be explained without full water vapour feedback on top of both the ice sheet albedo and CO2 effects.

We can wait for the post on Water Vapour and feedback effect for a response to this.

[Response: These feedbacks are indeed modelled because they depend not on the trace greenhouse gas amounts, but on the variation of seasonal incoming solar radiation and effects like snow cover, water vapour amounts, clouds and the diurnal cycle.

Water vapour is a feedback, not a forcing (though since people keep failing to understand the distinction I will do a post on this topic at some point).

There's one piece to that jigsaw which is not often discussed: the primary feedbacks (water vapour, clouds), which ultimately determine the magnitude of the imbalance, are mainly dependent on surface temperature change rather than the mere presence of GHGs or related energy fluxes.

You really need to account for the vertical structure of temperature (the lapse rate), and if you want your model to get a number of basic things right you need to include spectrally grey absorbers — plus the additional mixing in the troposphere (which depends on convection, and hence affects water vapour feedbacks) etc....

On the real planet, there are multitudes of feedbacks that affect other greenhouse components (ice alebdo, water vapour, clouds etc.) and so the true issue for climate sensitivity is what these feedbacks amount to.

This means that the water vapour greenhouse effect feedback depends on the surface specific heat, latitude and altitude; all of which affect temperature.

This «climate sensitivity» not only depends on the direct effect of the GHGs themselves, but also on natural «climate feedback» mechanisms, particularly those due to clouds, water vapour, and snow cover.

Based on evidence from Earth's history, we suggest here that the relevant form of climate sensitivity in the Anthropocene (e.g. from which to base future greenhouse gas (GHG) stabilization targets) is the Earth system sensitivity including fast feedbacks from changes in water vapour, natural aerosols, clouds and sea ice, slower surface albedo feedbacks from changes in continental ice sheets and vegetation, and climate — GHG feedbacks from changes in natural (land and ocean) carbon sinks.

Second, the feedbacks are all based on a series of assumptions that climate science will not question (water vapour, positive cloud feedback, no / tiny lapse rate change).

I tabled two papers on water vapour and feedback on recent threads.

However, there are other feedbacks (water vapour, lapse rate, clouds) which depend roughly linearly on dT, so you can rewrite the above as

The most credible of the contrarians, Richard Lindzen, has relied primarily on arguments that the feedback from water vapour, which plays a central role in climate models, might actually be zero or even negative.

The identified atmospheric feedbacks including changes in planetary albedo, in water vapour distribution and in meridional latent heat transport are all poorly represented in zonal energy balance model as the one used in [7] whereas they appear to be of primary importance when focusing on ancient greenhouse climates.

«As for alleged past water vapour feedback, this warming was not due to water vapour, as the feedbacks would have multiplied and fed back on themselves and led to the end of life on earth.

To date, while various effects and feedbacks constrain the certainty placed on recent and projected climate change (EG, albedo change, the response of water vapour, various future emissions scenarios etc), it is virtually certain that CO2 increases from human industry have reversed and will continue to reverse the downward trend in global temperatures that should be expected in the current phase of the Milankovitch cycle.

He argues that the current computer models which make more alarming predictions are unreliable, and based on the assumption of large positive «water vapour feedbacks».

One rational way to explain the short - lived nature of the MWP is to conclude that the water vapour the initial warming produced had a moderating, ie, negative feedback, on the warming.

The great simplicity of negative water vapour feedback on warming is that it is «symmetrical,» which is always a good sign that you might be on to a fundamental rule in nature, because natural systems usually have an elegant beauty that cut both ways.

If water vapour feedback was positive then due to the increased evaporation spurred on by the original warming in the MWP there should have ensued a period of elevated temperatures for thousands of years until the cooling of the Holocene as we dip into the next glacial period overwhelmed the positive water vapour forcing.

BH: Some of them are talking about climate sensitivity at 1.2 C, at 1.5 C. I think this is completely implausible because the basic energetics of the climate system responding to the additional greenhouse gas emissions almost from simple physics, has to be at least 1.2 C and possibly more before you begin to take into account any of the feedbacks in the system from water vapour in clouds and so on.

Existing climate models with a positive feedback from H2O are plain wrong, since they don't allow the heated water vapour to rise, forming clouds that contribute to global dimming, offsetting CO2 effects on temperature.

In addition, although the post 60s warming period is over, it has allowed the principal green house gas, water vapour, to kick in with humidity, clouds, rain and snow depending on where you live to provide the negative feedback that scientists use to explain the existence of complex life on Earth for 550 million years.

Based on the understanding of both the physical processes that control key climate feedbacks (see Section 8.6.3), and also the origin of inter-model differences in the simulation of feedbacks (see Section 8.6.2), the following climate characteristics appear to be particularly important: (i) for the water vapour and lapse rate feedbacks, the response of upper - tropospheric RH and lapse rate to interannual or decadal changes in climate; (ii) for cloud feedbacks, the response of boundary - layer clouds and anvil clouds to a change in surface or atmospheric conditions and the change in cloud radiative properties associated with a change in extratropical synoptic weather systems; (iii) for snow albedo feedbacks, the relationship between surface air temperature and snow melt over northern land areas during spring and (iv) for sea ice feedbacks, the simulation of sea ice thickness.

(2) It made the point (not an original point, but on the other hand one that is not widely known even among the cognoscenti) that water vapour feedback in the global warming story is very largely determined by the response of water vapour in the middle and upper troposphere.

The evidence of greenhouse warming, from cooling stratosphere to polar amplification, especially in the north, is clear — and the well - grounded feedbacks are on the positive side, from water vapour to albedo.

Much of the time these «outsider» critiques are not based on anything other than a desire to confuse (claims that IPCC doesn't mention water vapour feedbacks for instance, or that there is a deliberate attempt to downplay solar effects on climate or that the number of vineyards in England a thousand years ago implies that CO2 has no radiative effect) and have no traction in the scientific community.

1) CO2 is not rising significantly compared to earlier in the 20th century (Beck, Segalstad, Jaworowski) 2) OK, so CO2 is rising, but human sources are but a minor player (Howard Hayden, Spencer on WUWT) 3) OK, so human CO2 is significant, but its temperature effect is nonexistant (Heinz Hug) 4) OK, so CO2 has a temperature effect, but it is dwarfed by water vapour (Lindzen, Reid Bryson, Tim Ball 5) OK, so the CO2 temperature effect is not completely dwarfed by water vapour, but the sun is much more important (Svensmark, Shaviv, many others) 6) OK, so the solar output has been flat since the 50ies, but there are no net positive feedback (Lindzen again, Spencer again) 7) Actually, there has been no significant global warming (Watts, Singer + more), 8) Hey, all this warming is a) unstoppable anyway (Singer again) b) good for humanity (Michaels).

Now there were two papers put out by a Swiss team (you should know who) on consideration of European warming where they argued that natural effects could be ruled out; the first paper argued for strong water vapour feedback causing the 1980 to 1998 temperature rise and the later paper, using exactly the same data, argued for a reduction in aerosols causing a recovery in temperatures over the same period.