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Why is future sea level rise still so uncertain?

Filed under: — gavin @ 12 May 2021

Three new papers in the last couple of weeks have each made separate claims about whether sea level rise from the loss of ice in West Antarctica is more or less than you might have thought last month and with more or less certainty. Each of these papers make good points, but anyone looking for coherent picture to emerge from all this work will be disappointed. To understand why, you need to know why sea level rise is such a hard problem in the first place, and appreciate how far we’ve come, but also how far we need to go.

Here’s a list of factors that will influence future regional sea level (in rough order of importance):

  • ice mass loss from West Antarctica
  • ice mass loss from Greenland
  • ocean thermal expansion
  • mountain glacier melt
  • gravitational, rotational and deformational (GRD) effects
  • changes in ocean circulation
  • steric (freshwater/salinity) effects
  • groundwater extraction
  • reservoir construction and filling
  • changes in atmospheric pressure and winds

And on top of that, the risks of coastal flooding also depend on:

  • tectonic/isostatic land motion
  • local subsidence
  • local hydrology
  • storm surges
  • tides

If that wasn’t bad enough, it doesn’t even get into why some of the bigger terms here are so difficult to constrain – but more of that below.

Meanwhile, note that the factors listed above involve the whole Earth system: the oceans, the cryosphere, the atmosphere, the solid earth and lithosphere, and a full range of scales, from the city block and shoreline, to ice dynamics that change over kilometers, to GRD footprints, to the whole global ocean. While each of these elements has a devoted scientific community, sea level rise cuts across all the disciplines. And similarly, while each of these elements has a specialized modeling capability, there is no single model that encompasses all of this (not even close – as yet).

What this means is that estimates of future sea level rise are mixes of information from multiple sources, tied together in more or less sophisticated frameworks (this is the approach in the IPCC SCROCC report and the upcoming AR6) that attempt to build a full uncertainty range from all the disparate sources of information (coupled ocean-atmosphere models, hydrology models, ice sheet models, solid earth models etc.). To reiterate, there is no ‘climate model’ prediction of global sea level rise, though the climate models we often discuss here (the CMIP-class of models), do provide some of the inputs. This means that links and feedbacks between these different elements are not always coherent – e.g. the estimates of groundwater depletion (used for irrigation) or glacier melt might not impact the soils or the freshwater budget of the downstream rivers and ocean.

Two elephant seals in the Southern Oceans arguing about marine ice cliff instability.

Yes, but what about West Antarctica?

The West Antarctic Ice Sheet (WAIS) is the elephant seal in the aquarium. Ever since the 1970s it’s been suspected that it was prone to rapid collapse because the bedrock on which it sits is below sea level (and in some places, thousands of meters below sea level). More recent research constraining Eemian sea level (~125,000 yrs ago) has confirmed that WAIS collapsed at that time, adding 3 or more meters of sea level rise to the contribution from a much reduced Greenland Ice Sheet. Moreover, present day observations from gravity sensors (GRACE/GRACE-FO) show large ice mass losses from WAIS – dominated by the rapid retreats of the Pine Island Glacier and Thwaites glacier, and concomittent decreases in ice sheet elevation (from IceSat2).

Simplified schematic of atmosphere-ocean-ice interactions (Zalasiewicz et al, 2019)

There are many interesting observations and non-observations from WAIS that make this a challenging problem. First, the melting of the ice shelves and the retreat of grounding line is being driven from below as slighty warmer circumpolar deep water (CPDW) has been pushed onto the shelf. The CPDW is thought to be affected by the shift in the westerly winds around Antarctica which have increased in recent decades due to a combination of greenhouse gas forcing and the polar ozone hole (Miller et al, 2006).

Additionally, it looks like the anomalous meltwater from WAIS is causing the local ocean to freshen, stratify and cool (see Rye et al. (2020) or Sadai et al. (2020). Both of these effects make a straightforward connection between global mean warming and WAIS mass loss tricky.

But there is more. For instance, the bedrock topography under the ice sheet is still being refined. The last major revision (BedMap2) was in 2013 (Fretwell et al., 2013), but many areas remain without good data and important revisions are still being made (Morlighem et al., 2020). Also, the topography of the ocean bottom under the ice shelves is still being discovered using autonomous underwater vehicles, for instance, under the Thwaites last year. Meanwhile Bedmap3 is underway...

Furthermore, one important factor in how WAIS will affect sea level is how fast the lithosphere will respond to changes in the ice loading (part of the GRD effects mentioned above). If the mantle is very viscous, then the response is slow and it doesn’t add much to the global sea level change. But if it’s less so, then uplift is more rapid, and it can add more SLR, faster. Unfortunately, It turns out that the specific conditions under WAIS are less viscous than was thought (Pan et al., 2021).

Recent advances

Given, then, that we don’t have a suite of models with all the effects that we can analyze to give us a measure of the uncertainty, what can we do in the meantime? First, we can analyze the models we have and estimate the structural uncertainty among them – for the processes they include. This is what Edwards et al., (2021) do. Using the ISMIP6 and GlacierMIP simulation data and a statistical emulator they map out the responses of these models to the global mean temperature change and ocean-driven melting in Greenland and Antarctica. The nice thing about this is that you aren’t tied to the emission scenarios that were initially used in the MIPs, but you can’t independently calibrate the projections to paleo-climate changes, and you are stuck with the models that were used, some of which are a little out of date.

Alternately, you can take a single ice sheet model with better calibration to paleo-climate changes and drive it with climate model-derived boundary conditions as is done by DeConto et al., 2021. This doesn’t give you an estimate of full structural uncertainty (which is high), but perhaps is more internally consistent. However, the calibration that has been done on this model is (a little) controversial, and it’s worth discussing why.

Back in 2015, Pollard et al. (2015) found that their ice sheet model was overall too stable in that it wasn’t able match the large sea level changes that have been inferred for the Pliocene 3 million yrs ago (~20 meters) Eemian 125,000 yrs ago (6 to 9 meters). They added two destabilizing mechanisms, hydrofacturing of ice shelves and something called marine-ice cliff instability (MICI) and tuned the parameters to match the target. They then used this tuned version for future projections. However, the number of potential issues in the model (or any model really) is large – from uncertainties in the bedrock topography, the boundary conditions at bedrock itself, grounding line parameterizations, the resolution, the ice rheology, the lithospheric response etc. And MICI itself is quite uncertain Clerc et al., 2020 and as Edwards et al note, no model that contributed to ISMIP6 included a MICI-like mechanism. There is no guarantee that the specific destabilizing mechanisms used were the actual mechanisms at play in the warmer period. There may be other (unexplored) variations in the ice model that could have provided as good a match and that would have different sensitivity in the modern.

To their credit, DeConto et al. have extended the calibration to Pliocene sea level, the Eemian and the rate of change observed since 1992, though the Eemian constraint is the most important. And they did vary the mantle viscosity in the sea level calculations consistent with the Pan et al values. Even better, they also explored the sensitivity to a southern ocean response to Antarctic meltwater based on Sadai et al. (2020).

The question then is whether these two approaches are consistent and/or complementary.

Total land ice contribution to SLR (Edwards et al., 2021)
Antarctic contributions to sea Level scenarios from DeConto et al (2021)

So what do they show?

As one might expect, there are a lot of moving parts in these results. Many things have been varied. But there are some notable contrasts. First off, the main results for Antarctica in Edwards et al surprisingly suggest very little sensitivity to forcing scenario – basically just a continuation of the current rates of melt, which contrasts strongly with the DeConto et al result suggesting a threshold effect by 2060 between SSP1-26 (consistent with 2ºC) and SSP2-45 (or higher). Edwards et al. also look at some more ‘low probability/high impact’ runs (their ‘simulations for the risk averse’) which are more similar to the DeConto et al. results (around 20 cm from WAIS by 2100).

Remember that the biggest uncertainty is still the emission scenario, and the higher the scenario in terms of global warming, the more uncertain the ice sheet contribution is. Another key point made by DeConto et al. is that the world doesn’t stop at 2100. The consequences of even stable temperatures post-2100, has very large long term implications for sea level. For instance, even a 2ºC eventual warming is associated with around 1 meter of SLR just from WAIS by 2300.

Work to be done

These two papers illustrate the fundamental ingredients that will (eventually) get us to a more reliable estimate of SLR. The structural uncertainty explored by Edwards et al is broad, still incomplete, but essential. The calibration against past change in DeConto et al is also essential, even if the structural uncertainty they explore is narrower. A combined approach would be enlightening – using the DeConto et al model for the current ISMIP6 protocol, and extending that project to include the Eemian as an out-of-sample test might help.

Ice sheet science and the consequent sea level rise, like many cutting-edge topics, generally has a widening of uncertainty when the tools and theory start to really kick off. It is only later that this uncertainty is constrained as more observational data is brought to bear. Then, and not before, will projections start to narrow.

Until then, the most productive way to reduce uncertainties might just be to reduce emissions.

References

  1. R.L. Miller, G.A. Schmidt, and D.T. Shindell, "Forced annular variations in the 20th century Intergovernmental Panel on Climate Change Fourth Assessment Report models", Journal of Geophysical Research, vol. 111, 2006. http://dx.doi.org/10.1029/2005JD006323
  2. C.D. Rye, J. Marshall, M. Kelley, G. Russell, L.S. Nazarenko, Y. Kostov, G.A. Schmidt, and J. Hansen, "Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends", Geophysical Research Letters, vol. 47, 2020. http://dx.doi.org/10.1029/2019GL086892
  3. S. Sadai, A. Condron, R. DeConto, and D. Pollard, "Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming", Science Advances, vol. 6, pp. eaaz1169, 2020. http://dx.doi.org/10.1126/sciadv.aaz1169
  4. P. Fretwell, H.D. Pritchard, D.G. Vaughan, J.L. Bamber, N.E. Barrand, R. Bell, C. Bianchi, R.G. Bingham, D.D. Blankenship, G. Casassa, G. Catania, D. Callens, H. Conway, A.J. Cook, H.F.J. Corr, D. Damaske, V. Damm, F. Ferraccioli, R. Forsberg, S. Fujita, Y. Gim, P. Gogineni, J.A. Griggs, R.C.A. Hindmarsh, P. Holmlund, J.W. Holt, R.W. Jacobel, A. Jenkins, W. Jokat, T. Jordan, E.C. King, J. Kohler, W. Krabill, M. Riger-Kusk, K.A. Langley, G. Leitchenkov, C. Leuschen, B.P. Luyendyk, K. Matsuoka, J. Mouginot, F.O. Nitsche, Y. Nogi, O.A. Nost, S.V. Popov, E. Rignot, D.M. Rippin, A. Rivera, J. Roberts, N. Ross, M.J. Siegert, A.M. Smith, D. Steinhage, M. Studinger, B. Sun, B.K. Tinto, B.C. Welch, D. Wilson, D.A. Young, C. Xiangbin, and A. Zirizzotti, "Bedmap2: improved ice bed, surface and thickness datasets for Antarctica", The Cryosphere, vol. 7, pp. 375-393, 2013. http://dx.doi.org/10.5194/tc-7-375-2013
  5. M. Morlighem, E. Rignot, T. Binder, D. Blankenship, R. Drews, G. Eagles, O. Eisen, F. Ferraccioli, R. Forsberg, P. Fretwell, V. Goel, J.S. Greenbaum, H. Gudmundsson, J. Guo, V. Helm, C. Hofstede, I. Howat, A. Humbert, W. Jokat, N.B. Karlsson, W.S. Lee, K. Matsuoka, R. Millan, J. Mouginot, J. Paden, F. Pattyn, J. Roberts, S. Rosier, A. Ruppel, H. Seroussi, E.C. Smith, D. Steinhage, B. Sun, M.R.V.D. Broeke, T.D.V. Ommen, M.V. Wessem, and D.A. Young, "Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet", Nature Geoscience, vol. 13, pp. 132-137, 2019. http://dx.doi.org/10.1038/s41561-019-0510-8
  6. L. Pan, E.M. Powell, K. Latychev, J.X. Mitrovica, J.R. Creveling, N. Gomez, M.J. Hoggard, and P.U. Clark, "Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse", Science Advances, vol. 7, pp. eabf7787, 2021. http://dx.doi.org/10.1126/sciadv.abf7787
  7. T.L. Edwards, S. Nowicki, B. Marzeion, R. Hock, H. Goelzer, H. Seroussi, N.C. Jourdain, D.A. Slater, F.E. Turner, C.J. Smith, C.M. McKenna, E. Simon, A. Abe-Ouchi, J.M. Gregory, E. Larour, W.H. Lipscomb, A.J. Payne, A. Shepherd, C. Agosta, P. Alexander, T. Albrecht, B. Anderson, X. Asay-Davis, A. Aschwanden, A. Barthel, A. Bliss, R. Calov, C. Chambers, N. Champollion, Y. Choi, R. Cullather, J. Cuzzone, C. Dumas, D. Felikson, X. Fettweis, K. Fujita, B.K. Galton-Fenzi, R. Gladstone, N.R. Golledge, R. Greve, T. Hattermann, M.J. Hoffman, A. Humbert, M. Huss, P. Huybrechts, W. Immerzeel, T. Kleiner, P. Kraaijenbrink, S. Le clec’h, V. Lee, G.R. Leguy, C.M. Little, D.P. Lowry, J. Malles, D.F. Martin, F. Maussion, M. Morlighem, J.F. O’Neill, I. Nias, F. Pattyn, T. Pelle, S.F. Price, A. Quiquet, V. Radić, R. Reese, D.R. Rounce, M. Rückamp, A. Sakai, C. Shafer, N. Schlegel, S. Shannon, R.S. Smith, F. Straneo, S. Sun, L. Tarasov, L.D. Trusel, J. Van Breedam, R. van de Wal, M. van den Broeke, R. Winkelmann, H. Zekollari, C. Zhao, T. Zhang, and T. Zwinger, "Projected land ice contributions to twenty-first-century sea level rise", Nature, vol. 593, pp. 74-82, 2021. http://dx.doi.org/10.1038/s41586-021-03302-y
  8. R.M. DeConto, D. Pollard, R.B. Alley, I. Velicogna, E. Gasson, N. Gomez, S. Sadai, A. Condron, D.M. Gilford, E.L. Ashe, R.E. Kopp, D. Li, and A. Dutton, "The Paris Climate Agreement and future sea-level rise from Antarctica", Nature, vol. 593, pp. 83-89, 2021. http://dx.doi.org/10.1038/s41586-021-03427-0
  9. D. Pollard, R.M. DeConto, and R.B. Alley, "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth and Planetary Science Letters, vol. 412, pp. 112-121, 2015. http://dx.doi.org/10.1016/j.epsl.2014.12.035
  10. F. Clerc, B.M. Minchew, and M.D. Behn, "Marine Ice Cliff Instability Mitigated by Slow Removal of Ice Shelves", Geophysical Research Letters, vol. 46, pp. 12108-12116, 2019. http://dx.doi.org/10.1029/2019GL084183

67 Responses to “Why is future sea level rise still so uncertain?”

  1. 51

    @49, 48, 47 – I never doubted the Clausius-Clapeyron law for a second. But – it is not valid over a desert without significant rainfall, since the water vapor content remains unsaturated there.
    I would have liked to have believed the satellite data from ISCCP & NASA, because in a few centuries and at breathtaking speed mankind has reduced evaporation over many millions of km² of land area and continues to do so. (See 20)

    I had no idea that Nasa-Satelittes can not be trusted and apparently 25 years of time and money has been wasted here to produce wrong and still published data.

    I am also not so much concerned with the exact global water vapor content of the atmosphere, but with global cloud cover and with the question asked at the beginning:

    Why is future sea level rise still so uncertain?

    For my part, I will return this not entirely unimportant question with a very simple answer: “It will depend on whether humanity finds a concept that slows, stops or even reverses sea level rise.”

    …and here it is

    45,000 km³ of fresh water flows into the seas via rivers every year. Even a high annual sea level rise of 3.7 mm corresponds to “only” ~ 1300 km³ (3%).

    https://wiki.bildungsserver.de/klimawandel/upload/Wasserkreislauf.jpg

    This corresponds to 9L / m² over global land area and 18L / m² for the 50% agricultural area – far too little for a drought lasting 2 weeks to 2 months in a summer in the Rhine Valley at the 49th parallel.

    If you convert this volume into cumulus clouds, you get ~ 2 billion clouds, which improve the earth’s albedo all year round on 3.5 million km². The global cloud cover will improve by ~ 1%, which will cause a negative radiative forcing of
    ~ 0.21 W / m².

    https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter07_FINAL-1.pdf
    page 582

    That is far more than the current annual increase in radiative forcing caused by CO² – and would holistically resolve almost all problems caused by climate change.
    The volume of 1300km³ of water will also ensure an additional assimilation of 1.3-2.6 Gt of carbon in agriculture.
    This newly discovered Israeli / Egyptian climate protection concept starts with rain barrels, cisterns and larger rain retention basins which are equipped with an overflow onto unsealed terrain. But even the smallest stream and river can tolerate a small diversion outside of the drought and low water and is usually much cleaner than in the vicinity of the larger cities.

    Taking out as much CO² emissions as possible …
    but also evaporate as much water as possible through an increasing plant growth — is hopefully the global motto for the atmosphere of the future.
    Artificial, intelligent irrigation is instantly faster, 1000times cheaper and will have to be implemented anyway as an adaptation measure in many regions in the future.
    To make a virtue out of necessity – that’s what we need to do quickly.

    More info (which needs to be updated now)
    https://www.lumen-laden.de/products/ganzheitliche-alternative-klimaschutz-strategie/

  2. 52

    MS,

    Clement, A.C., Burgman R., and J.R. Norris 2009. “Observational and Model Evidence for Positive Low-Level Cloud Feedback.” Science 325, 460-464.

    Dessler, A.E. 2010. “A Determination of the Cloud Feedback from Climate Variations over the Past Decade.” Sci. 330, 1523-1527.

    “Estimates of Earth’s climate sensitivity are uncertain, largely because of uncertainty in the long-term cloud feedback. I estimated the magnitude of the cloud feedback in response to short-term climate variations by analyzing the top-of-atmosphere radiation budget from March 2000 to February 2010. Over this period, the short-term cloud feedback had a magnitude of 0.54 ± 0.74 (2s) watts per square meter per kelvin, meaning that it is likely positive. A small negative feedback is possible, but one large enough to cancel the climate’s positive feedbacks is not supported by these observations.

    Both long- and short-wave components of short-term cloud feedback are also likely positive. Calculations of short-term cloud feedback in climate models yield a similar feedback. I find no correlation in the models between the short- and long-term cloud feedbacks.”

    Yao, M.-S., and A.D. Del Genio, 1999: Effects of cloud parameterization on the simulation of climate changes in the GISS GCM. J. Climate, 12, 761-779, doi:10.1175/1520-0442(1999)0122.0.CO;2.

    Abstract:

    Climate changes obtained from doubled CO2 experiments with different parameterizations of large-scale clouds and moist convection are studied by use of the Goddard Institute for Space Studies (GISS) GCM at 4° lat × 5° long resolution. The baseline for the experiments is GISS Model II, which uses a diagnostic cloud scheme with fixed optical properties and a convection scheme with fixed cumulus mass fluxes and no downdrafts. The global and annual mean surface temperature change (DeltaTs) of 4.2°C obtained by Hansen et al. using the Model II physics at 8° lat × 10° long resolution is reduced to 3.55°C at the finer resolution. This is due to a significant reduction of tropical cirrus clouds in the warmer climate when a finer resolution is used, despite the fact that relative humidity increases with a doubling of CO2. When the new moist convection parameterization of Del Genio and Yao and prognostic large-scale cloud parameterization of Del Genio et al. are used, ?Ts is reduced to 3.09°C from 3.55°C. This is the net result of the inclusion of the feedback of cloud optical thickness and phase change of cloud water, and the presence of areally extensive cumulus anvil clouds. Without the optical thickness feedback, ?Ts is further reduced to 2.74°C, suggesting that this feedback is positive overall. Without anvil clouds, ?Ts is increased from 3.09° to 3.7°C, suggesting that anvil clouds of large optical thickness reduce the climate sensitivity. The net effect of using the new moist convection parameterization without anvil clouds is insignificant (from 3.55° to 3.56°C). However, this is a result of combination of many competing differences in other climate parameters. Despite the global cloud cover decrease simulated in most of the experiments, middle- and high-latitude continental cloudiness generally increases with warming, consistent with the sense of observed twentieth-century cloudiness trends; an indirect aerosol effect may therefore not be the sole explanation of these obervations.

    An analysis of climate sensitivity and changes in cloud radiative forcing (CRF) indicates that the cloud feedback is positive overall in all experiments except the one using the new moist convection and large-scale cloud parameterization with prescribed cloud optical thickness, for which the cloud feedback is nearly neutral. Differences in ?CRF among the different experiments cannot reliably be anticipated by the analogous differences in current climate CRF. The meridional distribution of ?CRF suggests that the cloud feedback is positive mostly in the low and midlatitudes, but in the high latitudes, the cloud feedback is mostly negative and the amplification of ?Ts is due to other processes, such as snow/ice-albedo feedback and changes in the lapse rate. The authors’ results suggest that when a sufficiently large variety of cloud feedback mechanisms are allowed for, significant cancellations between positive and negative feedbacks result, causing overall climate sensitivity to be less sensitive to uncertainties in poorly understood cloud physics. In particular, the positive low cloud optical thickness correlations with temperature observed in satellite data argue for a minimum climate sensitivity higher than the 1.5°C that is usually assumed.

    Text excerpts:

    “In every run without exception, global low cloud amount and middle cloud amount decrease when CO2 is doubled, contributing to a positive feedback.”

  3. 53

    MS, #51–

    I am also not so much concerned with the exact global water vapor content of the atmosphere, but with global cloud cover…

    Again, these are quite distinct beasts; clouds are *liquid* water, not vapor.

    NASA’s Earth Observatory:

    …while the places with the most water vapor in any month are always among the cloudiest, it is not always true that the cloudiest places are among the most humid locations. The tropics are both very humid and very cloudy, but in many months, the Southern Ocean is among the cloudiest places on the planet, even though the amount of water vapor is relatively low. This pattern occurs because cloud formation depends on both water vapor and air temperatures. The colder the air, the more readily any water vapor in the air will condense into clouds.

    https://earthobservatory.nasa.gov/global-maps/MYDAL2_M_SKY_WV/MODAL2_M_CLD_FR

  4. 54
    Piotr says:

    Matthias Schürle (51): I had no idea that Nasa-Satelittes can not be trusted and apparently 25 years of time and money has been wasted here to produce wrong and still published data.

    The problem seems to be with your understanding than with NASA satellites themselves. it was you who stated: “How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010?” and when asked about the source – you quoted … a paragraph on The International Satellite Cloud Climatology Project (ISCCP) – which deals with …. clouds, and nothing about “2mm”.

    MS(51) I am also not so much concerned with the exact global water vapor content of the atmosphere, but with global cloud cover

    then why make claims on the “ decrease of ~ 2mm absolute water vapor content“, INSTEAD of saying something about clouds? We can’t read your mind – we can only go by what chose as important to your argument.

    MS(51) and with the question asked at the beginning: Why is future sea level rise still so uncertain?

    I think the clouds are one of the least important source of this uncertainty –
    the article points to “ ice sheet science” as the factor that has to be constrained first. And until we get better handle on predicting of ice shelves,
    they conclude: “ the most productive way to reduce uncertainties might just be to reduce emissions“.

    If you want to promote rain barrels and other storage – my suggestion would be: do it the context of adapting to the future extremes weather events – helping to intercept some of the rains and provide them for human use (irrigation or other) when it is dry, but to should be from the view point of an individual or a community, as the scale is too small to effectively affect the macro hydrological flows – eg. to smooth the flood-drought extremes in a river – wetlands and hydroreservoirs have a better scale to do so. Not even saying about the ability to mitigate sea-level rise.

    So my suggestion is:
    – “write what you know (that you can prove)” – promote barrels as one way to ADAPT, for individuals and communities, to water supply changes caused by climate change. BTW, this being a low-tech would fit into Killian’s idea of simplification.

    – don’t try to sell it as way to _mitigate_ large scale climate change impacts – like changes hydrology on land and in sea level, because your all your barrels combined would have too small volume to have a noticeable effect on total river runoff or sea level rise.

  5. 55

    @52,53,54 – SORRY for my misinterpretation of:

    https://www.climate4you.com/ClimateAndClouds.htm#Clouds, evaporation and climate

    https://isccp.giss.nasa.gov/analysis/climanal1.html

    The graphs used there clearly show a decrease in atmospheric water and low cloud cover. @ Piotr – please note, that 99,7% of all atmospheric water is water vapor. The clouds contain only a 0,25-0,3%. Among the different cloud types, the highest long-term association between water vapour content and cloud cover is apparently seen in relation to low clouds, while other cloud types show little association. On a shorter time scale, however, the annual variation of water vapour and global cloud cover occur in concert with each other.

    Unfortunately, I overlooked the note explaining this discrepancy since 1998/99:
    ” Please note that the step-like change in atmospheric water content 1998-1999 may be related to changes in the analysis procedure used for producing the data set, according to information from ISCCP. The cloud cover data, however, should not be affected by this. ”

    However, we also experience a lower annual cloud cover from the fact that at least here in Europe & Germany the annual number of hours of sunshine (depending on the region and year) has often increased by more than 20% within the last 70 years:

    https://climate.copernicus.eu/sunshine-duration
    https://www.dwd.de/DE/leistungen/zeitreihen/zeitreihen.html?nn=480164

    This increase does not only take place in summer during the longer periods of drought, but alarmingly also in winter and spring. Only autumn often has a more or less constant solar radiation that reaches the earth’s surface.
    Due to the high position of the sun and the longer days, clouds naturally continue to have the greatest cooling effect in summer, which is why their loss is particularly painful in the increasingly frequent summer droughts. It would also be the time of the year, in which mankind could ideally produce additional (artificial) clouds with additional artificial irrigation.

    P(54) I think the clouds are one of the least important source of this uncertainty

    I think clouds are one of the most important sources of this uncertainty – one that we can also deal with.
    You also underestimate the roof areas of this world. The urban area sealed by humans is ~ 1% of the land area(1.500.000km²). With global mean values ​​for annual precipitation amounts of ~ 1000mm, there is a volume of precipitation over this area, that corresponds to a sea level rise of almost 4mm.
    With an estimated 25% roof area, rain barrels have the potential of 1mm sea rise. Streets, (parking) spaces and other urban areas often force water into the sewer system and through sewage treatment plants without need, which also causes high costs.
    The catchment area of ​​the Rhine alone, in which I live, has hundreds of thousands of springs, streams and rivers that are suitable for diversion to keep the water in the landscape, to fill up the water table, to rewet moors and forests.

    With a worldwide increased awareness that clouds are one of our best climate protection, and the global demand to wrest a small part of the runoff from the rivers of the world – we create a strong tool for climate protection in addition to CO² avoidance, that could withstand the sea level rise.

    There are not an infinite number of concepts for lowering sea level rise – in any case, meditation on the Mauna Loa and trust in human reason will not get us any further.

  6. 56
    Piotr says:

    Matthias Schürle(55):” Unfortunately, I overlooked the note explaining this discrepancy since 1998/99: Please note that the step-like change in atmospheric water content 1998-1999 may be related to changes in the analysis procedure used for producing the data set, according to information from ISCCP

    Well … here goes your decreasing trend… and your bitter criticisms of NASA and satellites: MS (51): “I had no idea that Nasa-Satelittes can not be trusted and apparently 25 years of time and money has been wasted here to produce wrong and still published data.”

    MS(55): “I think clouds are one of the most important sources of this uncertainty

    Based on what? Based on that the article opening this thread says it is …not?
    Based on your: “ @ Piotr – please note, that the clouds contain only a 0,25-0,3% of atm. water“?
    Based on the fact that even 100% of atm water is still MANY orders of magnitude less than water locked in land ice – hence even a tiny % change in the latter would outweigh even a massive change in atm water vapour, and even more so of something that makes at most … “0.3% of that atm vapour”?

    Perhaps you heard somewhere that clouds are the major source of the climate model uncertainty – yes, but they meant in predicting the temperature, NOT the sea-level.

    MS55: “ one that we can also deal with.

    How, other than via geoengineering?

    MS55: “in Europe & Germany the annual number of hours of sunshine (depending on the region and year) has often increased by more than 20% within the last 70 years

    Germany and even Europe are only a tiny part of “global”. And regional trends reflect regional changes in the atmospheric patterns – say position of a Jet Stream deciding what air masses you get + plus you get i recent decades reduction in aerosol emissions, from smokestacks and cars, which reduces the number of the available CCNs (cloud condensation nuclei).

  7. 57
    nigelj says:

    Matthias Schürle @51 appears to suggest we combat climate warming by increasing the atmospheric water vapour and thus cumulous cloud formation to reflect solar energy. But wouldn’t even more atmospheric water vapour, a greenhouse gas, increase radiative warming cancelling out the cooling effect? Googling my suspicions I found this which suggests they were right, and further problems manipulating cloud formation:

    https://isccp.giss.nasa.gov/role.html

  8. 58

    #57, nigel–

    If that’s Matthias’s proposal, the issue would seem to me to be, could we even meaningfully affect atmospheric water vapor in the first place?

    I have difficulty imagining that we could ever rival the natural evapotranspiration fluxes to a significant degree (though I admit I have no analysis backing this intuition.) And then consider the short atmospheric residence time… It makes me think of old King Cnut (AKA “Canute”) trying to hold back the tide.

    (Though I’ve read in recent years that contrary to the long commonly-held version of the tale, Cnut wasn’t megalomaniacal at all, but rather a wise king commending humility to his courtiers via a dramatic reductio ad absurdam.)

  9. 59

    @Piotr – Based on what? – Do I think you are at home in a country, where handguns are sold on the next corner and children often go to school with them?

    Here’s a list of factors that will (be)influence(d by clouds for the) future regional sea level (in rough order of importance):

    Do clouds influence the factor
    ice mass loss from West Antarctica – yes
    ice mass loss from Greenland – yes
    ocean thermal expansion – yes
    mountain glacier melt – yes
    gravitational, rotational
    and deformational (GRD) effects – no
    changes in ocean circulation – yes
    steric (freshwater/salinity) effects – yes
    groundwater extraction – yes
    reservoir construction and filling – yes
    changes in atmospheric pressure and winds – yes

    Here I propose an addition —
    *changes in the water cycle.* – yes

    The author says also:

    “Remember that the biggest uncertainty is still the emission scenario, and the higher the scenario in terms of global warming, the more uncertain the ice sheet contribution is.”

    So I could also say: if the cow shits – the sea level rises.
    Uncertainty of cloud -> is uncertainty of temperature -> is uncertainty of sea level rise. Don`t lose your head guy.

    My personal meta-factor is the albedo – and (low) clouds play an enormous role there. They keep ~ 20% of solar radiation off the earth’s surface.

    Even if the author meant CO² and other greenhouse gases in the first place by emissions – I claim that we as mankind are also increasingly influencing water (vapor) emissions.
    Every km² of burned rainforest, boreal forest or drained bog and wetland reduces global evaporation and increases the runoff into the oceans.

    You will probably have to be forced at your shotgun to recognize evapotranspiration as a heavyweight in the radiation budget.
    In the global radiation balance, ~ 80W / m² evaporation is a temporally and locally averaged value, which in summer can be up to ~ 350W / m² in real terms at noon. — Without any water, as is often the case in a desert, 350W / m² are then converted into heat and NOT into cooling clouds. –

    https://www.theworldcounts.com/challenges/planet-earth/forests-and-deserts/global-land-degradation/story

    On the other hand, the ~ +3.5W / m² radiative forcing, which is in accordance with the Paris Agreement on Climate Protection (~1.5 ° C) – is peanuts.

    P says: “Based on the fact that even 100% of atm water is still MANY orders of magnitude less than water locked in land ice – hence even a tiny % change in the latter would outweigh even a massive change in atm water vapour, and even more so of something that makes at most … “0.3% of that atm vapour”?

    I say yes: Most of the millions year old, millions of km³ antarctic land ice sheet is made out of tiny snowflakes. Falling out of clouds with its very tiny fraction of the global water.

    P asks: “How, other than via geoengineering?”

    I would call rain barrels, cisterns, groundwater charge and artificial irrigation more like home-engineering.
    Europe may be small – but God knows not the only continent affected by drought and temperature records.

  10. 60
    MA Rodger says:

    Kevin McKinney @58,
    (Your mention of King Cnut and his seaside demonstration of his kingly limitations to his obsequious courtiers reminds me of the explanation for Caligula’s declaration of war against the sea.)

    The Matthias proposal is perhaps spoilt by its delivery and the bells-&-whistles added about SLR as well as what appears to be a few errors.

    It is well established that the difference in warming between land and ocean is due both to the thermal lag of the ocean mass (a temporary thing) and also the increase of evaporation from the oceans (a permanent thing). I read this as being the central point being made by Matthias:- an increase in evaporation over land will reduce the warming.
    It is true that the land is becoming significantly less-wet under AGW and may well be significantly less-wet due to more direct human activity like chopping down trees and draining marshes. There is also a decrease in low cloud when low cloud is a cooling factor so less low cloud would presumably increase warming, but I wouldn’t like to speculate over any connection between drier land and decreased low cloud.

    But it seems what is fundamental to the Matthias proposal is humanity’s impact on the water cycle – specifically how much is being evaporated from land. A recent paper (CarbonBrief coverage HERE) has suggested that despite land becoming drier, on average AGW is increasing evaporation from land. So perhaps the actual point of the Matthias proposal is that humanity could boost the cooling effects of land evaporation. If such boosting were significant and remembering ‘what goes up must come down’, this would likely come with some big changes in climate, changes whose impacts may well rival AGW itself.

    I hope this interpretation assists the discussion and is not misrepresenting the Matthias proposal.
    (Perhaps I should add that the idea of using land water storage to combat SLR is ill-thought-out. If we are faced with 1m of SLR, we would have to somehow cover the continents with an average of 2m of water to reverse such a rise.)

  11. 61

    @nigelj 57,Kevin 58

    I posted this link in MS 51 and will repeat doing so.

    https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter07_FINAL-1.pdf

    Page 578-582

    7.2.1.2 Effects of Clouds on the Earth’s Radiation Budget

    The effect of clouds on the Earth’s present-day top of the atmosphere
    (TOA) radiation budget, or cloud radiative effect (CRE), can be inferred
    from satellite data by comparing upwelling radiation in cloudy and
    non-cloudy conditions (Ramanathan et al., 1989). By enhancing the
    planetary albedo, cloudy conditions exert a global and annual shortwave cloud radiative effect (SWCRE) of approximately –50 W m–2 and,
    by contributing to the greenhouse effect, exert a mean longwave effect
    (LWCRE) of approximately +30 W m–2, with a range of 10% or less
    between published satellite estimates (Loeb et al., 2009). Some of the
    apparent LWCRE comes from the enhanced water vapour coinciding
    with the natural cloud fluctuations used to measure the effect, so the
    true cloud LWCRE is about 10% smaller (Sohn et al., 2010). The net
    global mean CRE of approximately –20 W m–2 implies a net cooling effect of clouds on the current climate. Owing to the large magnitudes
    of the SWCRE and LWCRE, clouds have the potential to cause significant climate feedback (Section 7.2.5). The sign of this feedback on climate change cannot be determined from the sign of CRE in the current
    climate, but depends instead on how climate-sensitive the properties are that govern the LWCRE and SWCRE.

    @Kevin – “I have difficulty imagining that we could ever rival the natural evapotranspiration fluxes to a significant degree (though I admit I have no analysis backing this intuition.)”

    2-4mm sea level rise over 71% ocean area = 4,9 – 9,8mm over 29% land area.
    Now imagine a farmer after 2 weeks of summer drought – looking to his corn or whatever.
    5-10L/m² is about as much as a moderate summer thunderstorm delivers in precipitation.
    Even at the 49th parallel north, we can now see extended periods of drought between April and October. 50% of the global land area is used for agriculture and can easily evaporate a multiple of the sea level rise – theoretically, a similarly large volume can be sunk in the 30% forest areas, which in summer already partially die under heat stress and drought.

    I would like to show how this climate protection strategy could be implemented locally, using my city and its possibilities as an example. In the urban and rural district, 750,000 inhabitants live on an area of ​​1250km².

    This area extends from the western bank of the Rhine to the foothills of a low mountain range, which we call the Black Forest.
    On the relatively flat surface there are ~ 15-20 smaller quarry ponds, some of which are located directly on the banks of the Rhine, but some are also 4-8km away from the Rhine.
    These lakes were created through sand and gravel mining and mostly contain very clean groundwater. On the shores of the lakes, you can read the groundwater level of the area.

    With a 4km long and approx. 50cm thick water pipe we discharge approx. 475L / sec from the Rhine outside of the drought period – and into the groundwater of the Rhine plain. How much will this pipeline cost ? few million euros ?
    With 12,5 million m³ extra water per year it`s a fantastic buisness, as citizens here pay ~ € 2,-/m³.

    560km² of agricultural area will now have 22L/m² extra in summer available. Actually still far too little, as my m² garden easily slurps away 10L / m² after a long, hot, sunny day.
    Since the natural variability of our precipitation is somewhere between 700mm and 900mm / year, we can easily discharge 5-10 times the amount of water in a dry summer.

  12. 62

    Mathias, I tried to put a little quantitative flesh on the project you propose, per your #61 and its antecedents. Here’s what I came up with.

    Earth’s ocean surface is ~362 million km2, and a 2 mm ‘skin’ = 2/millionths of 1 km, so the volume of water cited implied by your SLR figure is ~724 km3. A hypothetical lake with that volume would rank 16th in the world.

    Now, how does that compare with natural fluxes? Annual precipitation over the globe is apparently a bit over 1000 mm. We’ll assume, probably a bit contrafactually, that that’s proportionate over land and sea, and that figure therefore applies to the oceans. So that’s pretty close to 3 mm/day, for around 1000 km3–a volume that would more than fill the world’s 14th largest lake. (Lake Ladoga, if you care).

    The Rhine takeoff pipe was spec’ed to carry 475L/s, which is about 41 million L in a 24-hour day. Or 0.000041 km3… which means you’d need a tad over 24 million of those babies.

    With a water supply equal to one Lake Ladoga per day. Compare the Amazon, with the greatest average discharge rate on Earth, @ 209,000 m3/s. That works out to ~18 km3/day. Call the daily total 50 Amazon River’s worth.

    And, don’t forget, power to pump it all–recall that E-P had put the volume of water needed for US pumped hydro storage at ~1 Lake Erie (480 km3). (But I forget the time frame involved just now… more than one day, I think.) Anyway, it’s a pretty significant amount, even considering that it’s on a global scale.

    This is all pretty rough, admittedly, but so far I’m not seeing this project as highly practical on the global scale–although you could certainly do it on a local scale, as your example shows.

  13. 63
    Piotr says:

    Matthias Schürle(55): “,i> I think clouds are one of the most important sources of this uncertainty ”
    ===
    Piotr(56) “Based on what? Based on the article opening this thread saying it is …not?
    Based on your own claim that “the clouds contain only a 0,25-0,3% of atm. water“?
    Based on the fact that even 100% of atm water is still MANY orders of magnitude less than water locked in land ice?
    ===
    Matthias Schürle(59) “Do I think you are at home in a country, where handguns are sold on the next corner and children often go to school with them “?

    That ….. definitely punched a major hole in my arguments ;-) Comparing to that you assigning me a wrong country – only the icing on that cake…. ;-)

    MS(59) “ So I could also say: if the cow shits – the sea level rises.

    that’s … a surprisingly accurate metaphor for your argument here.

    MS(59) “Most of the millions year old, millions of km³ antarctic land ice sheet is made out of tiny snowflakes.

    ….which took them close to …. a million years. I bet that if you keep pilling up your “ cow shits ” for a million years – you would end up with a quite an impressive pile too. But who has the million years to wait for that….

    MS(59) “ Uncertainty of cloud -> is uncertainty of temperature -> is uncertainty of sea level rise

    The first part (“ Uncertainty of cloud -> is uncertainty of temperature “) sounds right since …this is what I have tried to explain to you in my P(56) by saying:
    “Perhaps you heard somewhere that clouds are the major source of the climate model uncertainty – yes, but they meant in predicting the temperature, NOT the sea-level.”
    Unfortunately, the rest of you post indicates that you are just saying it, without applying to your argument, e.g.:
    MS(59) “ Most of the millions year old, millions of km³ antarctic land ice sheet is made out of tiny snowflakes.
    which means that you are still talking about clouds as a SOURCE OF WATER, not clouds as affecting temperatures.

    As for your second arrow, i.e.: “[clouds-caused] uncertainty of temperature -> is uncertainty of sea level rise
    – iceshelves are primarily destabilized by Antarctic seawater. I doubt your tiny increase in cloudiness over Germany would really alter that.

    MS(59) Don`t lose your head guy

    Ignorance correlates with arrogance.

  14. 64
    Piotr says:

    Nigel: “Matthias appears to suggest we combat climate warming by increasing the atmospheric water vapour and thus cumulous cloud formation to reflect solar energy.
    Kevin: “if that’s Matthias’s proposal…
    MARodger: “perhaps the actual point of the Matthias proposal is that humanity could boost the cooling effects of land evaporation

    It reminds me my childhood summers in the mountains, laying on a grass, next to my brother and my cousin, pointing at a cumulus in the sky – “ It’s bird! It’s plane! “It’s a …. definitely not the Superman, since we don’t have that imperialist cartoon on our TV!“.

    Our Matthias’s style reminds me also Trump: he moves from topic to topic, often making contradictory claims, and those who are trying to make sense of it – latch on the first recognizable argument and dispose of the rest. “ It’s bird! (ignore plane thing garbage) .

    For example – his 1st post (20) starts with: “Water vapor, and not CO2, is the most important greenhouse gas.” So by increasing evaporation, he didn’t want to cool off Earth through higher cloud albedo (Nigel and Kevin) nor do evaporative cooling (MAR), but to …warm it even more (“the most important greenhouse gas”!)??? How this would help with the topic of this thread – SLR?
    Then a couple paragraphs below, he hints using the increased evap. to …. lower SL – via directing rain water into the air instead of allowing it to flow to the ocean. So which is it?

    Maybe not important, since with his claims on water vapour trends proven false, it turns out he wasn’t interested in the vapour, but in clouds.

    When we pointed that the clouds contain much too little water to directly affect SLR – and the actual influence of clouds is only indirect via albedo – he claims that this … is what he meant all the time, and … almost immediately contradicts himself by arguing:
    Most of the millions year old, millions of km³ antarctic land ice sheet is made out of tiny snowflakes
    Obviously he is no longer talking about cloud albedo.

    And what he lacks in logic and knowledge he makes up with arrogance:

    I had no idea that Nasa-Satelittes can not be trusted and apparently 25 years of time and money has been wasted here to produce wrong and still published data.
    after he missed”the step-like [drop] in atmospheric water content 1998-1999 may be related to changes in the analysis procedure” in the fig description.

    Or his response to Gavin:
    – Gavin:“ Remember that the biggest uncertainty is still the emission scenario, and the higher the scenario in terms of global warming, the more uncertain the ice sheet contribution is.
    – Matthias: “So I could also say: if the cow shits – the sea level rises […] Don`t lose your head guy.
    Touche!

    With NASA and Gavin put in their place in such a spectacular way, Matthias highly technical response to me ​“ Do I think you are at home in a country, where handguns are sold on the next corner and children often go to school with them “?
    seems mild by comparison, if a tad perplexing. Even if I did live in the US…:-)

  15. 65
    nigelj says:

    Matthias Schürle @61, thanks for the link on “Effects of Clouds on the Earth’s Radiation Budget” however it doesn’t change what I said or invalidate the study in the link I posted which showed its not clear that trying to increase the numbers of low level clouds by enhanced evaporation would actually cool the planet. There would certainly be big side effects with changes to rainfall.

    Its also not clear whether you could get enough enhanced plant growth to cause enough of a difference to atmospheric water vapour and cloud formation. Your numbers mostly focus on processes happening long term in equilibrium. It’s change that counts.

    I also note that there has been enhanced plant growth at scale due to the extra CO2 fertilisation process but it has not cooled the climate.

    I see where you are coming from and such ideas are interesting.

  16. 66

    #64–

    “…children often go to school with [handguns]…”

    A gross irrelevancy, of course–but just for the record, children do *not* often take handguns to school in the US. (Though admittedly, part of the reason is that doing so is heavily penalized, and enforcement is locally quite intense.)

    You hear of instances, of course, but they are rare enough to be newsworthy still.

  17. 67

    @ Kevin – “Now, how does that compare with natural fluxes? Annual precipitation over the globe is apparently a bit over 1000 mm.”

    Here are some numbers of the global water cycle and radiation balance:

    https://wiki.bildungsserver.de/klimawandel/upload/Wasserkreislauf.jpg
    https://upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Sun_climate_system_alternative_(German)_2008.svg/440px-Sun_climate_system_alternative_(German)_2008.svg.png

    80W/m² * 24h * 365d : 0,675KWh (Evaporation energy of 1kg water) = 1038mm(L).
    If you estimate SLR only 2mm/year – over land area this is 4,9mm (0,47% of natural flux = 0,376W/m²). This is a ~ 10% ! of radiation forcing since 1750 !

    With a 475L / sec pipe in Karlsruhe
    we could manage 20% for our 1250km² area. If possible, it is important to switch from groundwater abstraction to river water or bank filtrate, on the one hand to fill up (ground) water reservoirs and to wrest as much km³ as possible from the sea level.
    Any concept to mitigate the effects of climate change naturally requires a global scale. If science realizes that water has always played an outstanding role in saving a burning house, I have not the slightest doubt about feasibility.

    A discharge from a stream or river does not always have to be accomplished with pumps and energy expenditure. – You can often even generate electricity with small hydropower just further up in the steeper terrain. Um die Vielzahl der möglichen Entnahmestellen für ein einzelnes Einzugsgebiet zu demonstrieren – hier die Donau in Österreich als Beispiel:
    https://lumen-laden-de3.webnode.com/_files/200006581-f07b8f07bb/flusssystem_oesterreich2w.jpg

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