I think that the second thing you would have to do is show that 21st century aerosols are somehow higher than late 20th century aerosols between 15km and the tropopause
I fail to see how this is relevant. Pre-2000 SAOD data was incorporated into models and not assumed to be zero due to Mount Pinatubo. Models do, however, assume that the post-2000 SAOD is negligible (see below) because no major volcanic events occurred after that point. I therefore cannot see any relevance between this comment and the paper because pre-2000 SAOD data is already incorporated but perhaps someone could explain the relevance to me.
The relevant issue is whether the assumption that post-2000 SAOD is negligible is valid or not. Vernier et al 2011, Ridley et al 2014 and Santer et al 2014 demonstrate that this assumption is incorrect and so models miss the cooling impact introduced by smaller volcanic events that occurred after 2000 (most of which occurred after 2005).
Perhaps a time line would be helpful:
1992 to 2000 – Large aerosol increase caused by Mount Pinatubo in 1992 and fading to near zero around 2000 (
Source – Columbia University). This is factored into models.
1993 – First year of AERONET data (
source).
1995 – The first year of AERONET data used by Ridley et al 2014.
2000 – The year in which models include no stratospheric aerosol impacts. From Ridley et al 2014, “The climate model simulations evaluated in the IPCC fifth assessment report [Stocker et al., 2013] generally assumed zero stratospheric aerosol after about 2000, and hence neglect any cooling effect of recent volcanoes (see Figure 3 of Solomon et al., 2011).” The Stocker et al 2013 (IPCC AR5 Technical Summary) reference points to
Box TS.3
2004/2005 – Year when the "average" of model runs started to deviate from observations (
see image from Schmidt et al 2014). This is subjective, of course, maybe one would suggest 2002/3. It matters little.
2005 – Year when Ridley et al 2014 find a notable increase in SAOD in the data.
To find the relevant impact on models, you need to study the change in SAOD post-2000. Again, this is done in the paper:
Ridley et al Figure 3
[image
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Fig. 3 - (a) Estimated global mean radiative forcing is shown for datasets from Sato et al. (orange), Vernier et al. (blue) and AERONET mean (black) with 25th to 75th percentile range (grey). The dotted line indicates the baseline model used in many climate model studies to date, which includes no stratospheric aerosol changes after 2000.
(b) The temperature anomaly, relative to the baseline model, including the AERONET mean (black), median (white), and 25th to 75th percentile range (grey), Vernier et al. (blue), and Sato et al. (orange) forcing computed for each dataset
(c) the total global temperature change predicted by the Bern 2.5cc EMIC in response to combined anthropogenic and natural forcing, including the reduced warming when considering the stratospheric aerosol forcing from the three datasets.
The paper demonstrates that the incorrect assumption that SAOD past 2000 was zero misses a cooling impact of increased SAOD, most note ably after 2005. Therefore, part of (but certainly not all) of the recent discrepancy between models and observations can be explained by the fact that models do not include up-to-date volcanic aerosol information. Incorporating this correction would drop the "average" model outputs closer to observations. This is an example of observation improving model projections, so I'm unsure why those skeptical of models would try to (erroneously) discredit this research.
However, the authors have no way of showing that as that data does not exist pre AERONET
Again, I fail to see how this is relevant. Pre-2000, models incorporated SAOD data following the Mount Pinatubo eruption (Stocker et al, 2013). It was only after 2000 that models incorrectly assumed SAOD was zero. Therefore, this is the period of focus for the research. This entire period occurs when AERONET data exists. I should note that prior to AERONET data, there was SAGE II, CALIPSO, COMOS/ENVISAT and OSIRIS/Odin satellites (as used in Vernier et al, 2011). So even if it were relevant, I don’t believe the statement is true.
So given 2 facts, that there were more aerosols than previously thought and the presence of the pause they assume that there has been an increase in the early 21st century. The third option of ‘there were always more aerosols than we thought’ is ignored for the favored conclusion.
1. The post-2000 SAOD was greater than 0, yes.
2. The post-2000 SAOD increases, most notably from 2005-2011, which adds a cooling trend that is currently unaccounted for in models due to the incorrect assumption.
3. This appears to be incorrect. The pre-2000 SAOD data is incorporated into models.
The attribution of these aerosols to increased volcanic activity is pure speculation on the part of the authors
I don’t believe this is true. What information do you have to support this claim? I also claim if this is relevant. The issues is that aerosols have impacted the SAOD post-2000, unlike the assumption carried in models, which would have imposed a cooling trend on global temperatures. I fail to see how or why it's important to anything relevant if they come from volcanoes, other natural sources or anthropogenic sources.
The paper itself seems to suggest otherwise. Ridley et al 2014 describes numerous volcanic events that correspond to increases in SAOD. See Figure 1 from Ridely et al 2014:
[image
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Fig. 1 (a) The SAOD time series for the period 1995 – 2013 for satellite data from Vernier et al. (blue), Sato et al. (orange), AERONET mean, averaged from 30-45°N, (white) with 25th to 75th percentile uncertainty (grey shading), Tsukuba lidar retrievals (36.1°N, 140.1°E) above the tropopause (thick black line) and 15 km (thin black line), and aerosol sonde measurements at Laramie (41°N) above the tropopause (red dots) and 15 km (red crosses). Potentially important equatorial (solid lines) and mid-to-high latitude (dashed lines) volcanic eruptions are shown for Ulawun (Ul), Shiveluch (Sh), Ruang (Ru), Reventador (Re), Manam (Ma), Soufrière Hills (So), Tavurvur (Ta), Kasatochi (Ka), Sarychev (Sa), Eyjafjallajökull (Ey), and Nabro (Na). (b) Ratio of integrated optical depth above the tropopause to that above 15 km from three different lidars and from the in situ observations. The inset contains the same data on a log scale to indicate the ratios greater than 5 that are cropped for clarity on Fig. 1 (a).
The fact that they don’t try and support this claim with hard data suggests to me that they did attempt to do so but found the evidence lacking. In my experience with “climate science” when you ask yourself ‘why didn’t they do X since it’s so obvious’ the answer usually is that they did and didn’t get the answer they wanted.
This seems completely false. It is certainly not supported by anything else said in the post because everything else said in the post is unsupported by the paper or any evidence. I don’t believe such unsupported statements belong in this conversation. Especially ones that attempts, with zero supporting evidence, to degrade all published climate science. In keeping with the comments regarding the quality of discussion on climate change, I don’t believe a quality conversation can happen as long as comments like this persist.
