Review of the Draft Climate Science Special Report (2017) / Chapter Skim
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Appendix A: Line Comments
Appendix A: Line Comments
Pages 63-116
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From page 63... ...
In the early days of USGCRP the models were primarily atmosphere models with radiative forcing and some feedback loops. Today's models have become more fully coupled system models and hence the term "Earth System models" is more appropriate.
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From page 64... ...
See also main text remark about using slope-based statements. 21 P14/L5 R For western United States temperatures, it would be wise to add a terse qualifier from the discussion in the chapter, e.g., that changes in circulation might be partly responsible for the enhanced warming in the West and suppressed warming in the Southeast, lest an unsuspecting reader surmise that one area is more susceptible to GHG increases and the other less so.
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From page 65... ...
25 P14/L16-19 R The statement here about committed warming seems to be at odds with some papers, including Mathews and Weaver, 2010 (and others cited in main text for Section III.14) , which show that there would be no additional warming if human GHG emissions were to immediately cease.
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From page 66... ...
reductions are projected in western United States winter and spring snowpack are not consistent. Some explanation is needed, e.g., that the first refers to increased precipitation and the second refers to a reduction in the proportion of snowfall to total precipitation due to warming.
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From page 67... ...
There is strong evidence that western United States snowpacks have already been decreasing, so the sentence should say "continued reductions." The phrase "assuming no change in current water-resources management" strays into impacts, policy, and adaptation. It is sufficient to say that temperature changes will overwhelm any increases in precipitation in many places, leading to reductions in snowpack (and summer soil moisture)
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From page 68... ...
Recommend changing to "all" or explaining. 54 P22/L19-26 R It would be helpful if all of the conclusions on differences between local and global sea level rise were quantified (e.g., "0.2 m more or less than the global average")
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From page 69... ...
Recommend adding "but the magnitude of carbon release is currently uncertain" to the end of this statement. See comments in Section III.11 of main text.
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From page 70... ...
Also, the National Academies reports on climate intervention stress the differences between solar radiation management and CO2 removal and to reflect this, discussion of the two topics should be in separate bullets (see also main text)
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From page 71... ...
Now, it reads like a series of ungrounded assertions. 82 P33/L26 S "quite unpredictably" should be replaced with a more appropriate word or phrase 83 P34/L9-13 R For most readers, the contrast between increasing Antarctic sea ice and a shrinking Antarctic ice sheet will be unclear.
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From page 72... ...
86 P34/L28 V Use of a different length of the averaging period for the start and the end of the interval is confusing. See Section II.2 of main text regarding better statistical approaches for reporting observed changes.
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From page 73... ...
102 P39/L15-23 R The changes described in this paragraph should be better quantified, with uncertainty or statistical significance noted. See Section II.2 of main text.
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From page 74... ...
128 P52/L23-28 R This paragraph places too much emphasis on the importance of improving climate models. 129 P55/L5-6 R Consider providing a range or upper limit to projected changes in climate over the next 100 years.
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From page 75... ...
Geophysical Research Letters 40(19)
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From page 76... ...
146 P90/L6-7 R Text should clarify that only the most explosive volcanic eruptions lead to aerosol reaching the stratosphere, where they can have global climate effects. Most volcanoes affect only regional climate due to short lifetime of aerosols in the troposphere.
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From page 77... ...
164 P100/L1-5 S Suggest mentioning the interaction of warming oceans with sea ice and the subsequent acceleration of ice sheet loss. 165 P100/L16 V Text neglects to mention that snow is present in mid-latitudes where it makes a big difference in absorbed solar in springtime.
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From page 78... ...
2013. Ensemble projections of wildfire activity and carbonaceous aerosol concentrations over the western United States in the mid-21st century.
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From page 79... ...
177 P108/L16- V "… only a few very specific types of aerosols (for example, from 17 diesel engines) are sufficiently dark that they have a positive radiative forcing." This sentence should be deleted as it appears to minimize the impact of absorbing aerosols.
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From page 80... ...
Geophysical Research Letters 35(12)
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From page 81... ...
Perhaps "depends primarily on prior emissions and ..." 187 P152/L9 S It is worth mentioning that it is very unlikely that the atmospheric concentration of CO2 will be below 400 ppm in this century. 188 P152/L30 S Chapter 2 is referred to as Scientific Basis, but the title of Chapter 2 is Physical Drivers of Climate Change.
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From page 82... ...
199 P159/32- R This section should discuss why models differ in their P161/L7 calculation of climate sensitivity. 200 P160/L25 S CMIP6 is unlikely to be much farther along by the time this report is issued.
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From page 83... ...
. The Committee has recommended deleting this figure, as noted in the main text.
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From page 84... ...
Further, the structure and strength of regional temperature and precipitation impacts of these recurring modes of variability may be modified due to a change in the background climate." 219 P188/L5 S This sounds more like attribution than detection in the usual formulation. 220 P188/L3-37 S Can any of these changes be quantified, even in a relative sense?
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From page 85... ...
Geophysical Research Letters 29(24)
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From page 86... ...
235 P219/L9-10 R This statement would be strengthened considerably with a time series plot to back it up. Such a figure could then be revisited in a subsequent figure with the GCM-simulated past and future temperatures.
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From page 87... ...
Geophysical Research Letters 34(18)
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From page 88... ...
88 Appendix A # page/line V/R/S 257 P240/Fig. V Gray boxes in Figure 6.5 presumably are where insufficient 6.5 observations exist, and the CMIP5 data have been masked in the same places.
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From page 89... ...
268 P255/L27- R This passage seems to be a vehicle to discuss a single study. 29 ETCs are surely more important in winter, and ETCs are surely a less important factor in summer in many NCA regions than other factors (e.g., tropical cyclones, southwest monsoon, other summertime convection)
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From page 90... ...
280 P281/L3-6 R Important to note here that the "dust bowl" was not a purely natural phenomenon -- it was exacerbated by human land management practices. 281 P281/L29 R This section should note that the three characterizations of drought also have a varying range of timescales and are implicitly defined as deficits relative to some notion of what constitutes sufficient water (precipitation, soil moisture, stream flow)
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From page 91... ...
295 P284/L33- V In the statement, "less sensitivity to temperature increases than to 34 precipitation variations, which have increased over the 20th century," the juxtaposition of a directional temperature change and an increase in magnitude of precipitation variations is confusing. The quantity of soil moisture should be sensitive to total moisture input, not to the interannual variability.
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From page 92... ...
Soil moisture percentiles based on total column soil moisture (from multiple land surface models) are already used in NOAA's input to the U.S.
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From page 93... ...
. Beyond the studies cited, authors might also consider mentioning the well-established indirect effects of human activities on wildfire activity in the western United States: warmer temperatures, earlier snowmelt and runoff, and in many areas and times of year, lower soil moisture.
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From page 94... ...
Some commentary about the difficulty of projecting changes in severe storms would therefore also seem appropriate to include here. 323 P309/L10- R Is it worth noting here that Hartmann et al., 2013 found 19 increases in tropical cyclone activity to be "Virtually certain in North Atlantic since 1970?
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From page 95... ...
in tropical cyclone frequency" instead of referring to "the sign of the change in tropical cyclone frequency." 330 P311/L19- S What is the difference between consistency and consensus? 20 331 P312/L9-11 S This sentence should be posed as a statement and not a question.
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From page 96... ...
2010. Temperature-associated increases in the global soil respiration record.
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From page 97... ...
2010. Temperature associated increases in the global soil respiration record.
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From page 98... ...
367 P345/L1 R Stating the growing season changes are "more variable" using referenced figures is not an apt comparison, since Figure 10.3 is a map and Figure 10.4 is a time series. 368 P345/L16- S Are not plant hardiness zones based on temperate and growing 17 season length?
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From page 99... ...
379 P370/L25- S Sea level rise should also be mentioned. 27 380 P370/L25- S Lines 31-33 seem to serve the same purpose as 25-27, but state 33 things in less obscure terms.
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From page 100... ...
395 P373/L30- R "Internal climate variability alone could not have caused 31 recently observed record low Arctic sea ice extents (Zhang and Knutson 2013) ." A probability associated with this statement should be provided, if possible.
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From page 101... ...
Recommend restructuring to something like, "Approximately 50% of the total global soil carbon is found in boreal forest and tundra ecosystems." Also, please clarify whether this value contains carbon contained in permafrost. 409 P376/L16- R The math here is unclear here -- 50% decline between 1967 and 17 2012 (45 years)
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From page 102... ...
413 P377/L36 R The sentence: "Ice mass loss… has steadily declined" is confusing, as it seems to indicate that the rate of mass loss is decreasing around the Gulf of Alaska. That would be surprising given that the Arctic is warming rapidly, where mass loss from the biggest single ice sheet (Greenland)
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From page 103... ...
Note also that P381/L9 much of the CH4 released is likely to oxidize to longer-lived CO2. 430 P382/L10- S "Climate models have been predicting… for more than 40 11 years." To make the meaning completely clear, it would be better to say "For more than 40 years, climate models have been predicting…" 431 P383/L12 S Summary sentence simply reiterates previous text and does not integrate the key finding, evidence base, and key uncertainties in a concise way.
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From page 104... ...
DOI: 10.1029/2008GB003327. 438 P385/L38 S Recommend revising "…is affecting coastal erosion" to "is increasing coastal erosion." 439 P386/L4 S Consider replacing thermohaline circulation with MOC or AMOC?
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From page 105... ...
Consider replacing with "Assessment of vulnerability to rising sea levels…." Then, the last sentence could simply begin: "A risk-based perspective on sea-level rise points to the need for an emphasis on how changing…." 451 P412/L12 S Consider rewording to read: "1) increased volume of seawater from thermal expansion of the ocean as it warms, and 2)
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From page 106... ...
(2015) to the list of references for ice mass loss in the Bellingshausen Sea region.
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From page 107... ...
2013. Oceanic control of sea level rise patterns along the East Coast of the United States.
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From page 108... ...
. global average surface ocean acidity .
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From page 109... ...
502 P459/L38 R Recommend providing the comparison of the rates of N2O production through this mechanism and terrestrial anthropogenic production 503 P462/L16 V The full citation to "Rahmstorf et al., 2015" is not included in the References section. 504 P463/L20 V This web-site for CDIAC ocean data is in the process of being subsumed into NOAA, and may be unavailable soon.
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From page 110... ...
512 P482/L7-8 R Statement would benefit from clarification that the Paris goal is not exactly the same as 2°C or 1.5°C, it is "Holding the increase in the global average temperature to well below 2°C above pre industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels." 513 P482/L28- V Distinguishing between committed warming and committed 37 emissions is important here. The different scenarios diverge slowly first because the problem is intrinsically one of cumulative emissions and second because, in the near term, annual emissions on trajectories of ambitious mitigation and continued high emissions are similar and diverge only through time.
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From page 111... ...
520 P484/L32 V It is a little misleading to say that the concept of balance between sources and sinks in the Paris Agreement implies that CO2 emissions need to drop to zero. The definition of a range of warming targets (any warming target)
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From page 112... ...
Just as progress on climate change requires extensive science, so will balanced consideration of climate intervention. 533 P489/L16- R Recommend using this paragraph as the introduction to climate 25 intervention, not the concluding one.
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From page 113... ...
549 P505/L3-5 R This should also be stated in Chapter 12 on SLR and currently is not. 550 P505/L16- V An example of something like a tipping point was the 27 accelerated loss of Arctic sea ice about 10 years ago and the
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From page 114... ...
2014. Impact of reduced Arctic sea ice on Greenland ice sheet variability in a warmer than present climate.
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From page 115... ...
SUGGESTED GLOSSARY TERMS Aerosol-cloud interactions Aerosol-radiation interactions Agricultural drought Atlantic meridional Albedo Anticyclonic circulations overturning circulation Atmospheric blocking Atmospheric river Baroclinicity Bias correction Carbon dioxide removal Climate intervention climate sensitivity CMIPs (general description) CO2 equivalent CO2 fertilization Cryosphere Denitrification Deoxygenation Dynamical downscaling Earth system models Empirical statistical Effective radiative forcing Eutrophication downscaling models Extratropical cyclone Geoengineering Global temperature potential Global warming potential Hydrological drought Hypercapnia Hypoxia Ice wedge Instantaneous radiative forcing Intended nationally Long wave cloud radiative determined contributions IPCC effect (INDCs)
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From page 116... ...
116 Appendix A Paris Agreement Pattern scaling Perfect storms Permafrost Permafrost active layer Petagram Positive feedback Proxies Radiative forcing Representative concentration Relative sea level Rossby waves pathways Saffir-Simpson storms Scenarios Sea level pressure Shared socioeconomic Shortwave cloud radiative Snow water equivalent pathways effect Special Report on Emissions Solar radiation management Structural uncertainty Scenarios Teleconnections Thermohaline circulation Thermokarst Tipping elements Tipping points Transient climate response Undersaturation (vs. Tropopause Urban heat island saturation)
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