Can trends in flying, shipping and agriculture taken with a weaker solar cycle mean we don’t really need Geo-engineering ? By Dr Chris Barnes Bangor Scientific and Educational Consultants June 2013.
Dr Barnes Homepage http://www.drchrisbarnes.co.uk
A very brief review of geo-engineering by ocean iron seeding and stratospheric solar radiation management is made. The unforeseen dangers of ocean iron seeding may easily outweigh those of sulphate injection SRM. Drivers for climatic change are very briefly reviewed. Aerosols are discussed, particularly in the light of natural and anthropogenic sources and there stronger than previously thought ability as negative climate forcers. Sulphate aerosol in particular appears to be on the increase, contrary to the stated claims of some. Coincidental Sulphate injection by the sub -sonic air fleet, as a result of agriculture and ship tracks, coupled with a weaker than expected present solar cycle and a predicted even weaker next solar cycle is thought sufficient to exclude the need for geo-engineering at present. A small continued degree of warming may be economically and agriculturally more desirable than a Maunder minimum style cooling. Present figures seem to indicate that warming has halted. Erring on the side of caution the air fleet should perhaps not for the present switch to very low sulphur fuel. In addition to increasing aerosols, contrail avoidance technologies may already be impacting positively in terms of stabilising climate. Our ordinary air fleet used appropriately may be sufficient to perform all the world's climate and/or weather engineering until at least the year 2040.
For the past few decades there have been a number of proponents of geo-engineering and its attendant methods of climate mitigation of supposed global warming (1-3). The most shocking example is an illegal experiment in ocean iron seeding carbon sequestration which has already taken place (4). This action was illegal according to a previous definition by Reyfuse et al 2008 (5). There has also been much talk about and indeed many proposals for causing cooling by stratospheric sulphate injection see Rasch et al (6). Government committees have also been set up (7). Although the effectiveness of bringing this about by re-routing aircraft has recently been challenged by Laakso et al 2012 (8).
The purpose of this present work is to show that taken together with other forms of natural and anthropogenic aerosol injection and reduced solar radiation there is presently sufficient coincidental
stratospheric sulphate injection as a result of the subsonic aviation fleet operating at normal heights below the tropo-pause to offset current warming without the need to geo-engineer. This appears to be borne out by other studies of the present author (9).
Particularly as some recent findings tend to suggest that the last few decade's trend in warming has at worst slowed (10) or ceased (11) or at best even reversed (12).
Warming or cooling there are only four real known parent drivers for change. These are anthropogenic change, tectonic change (volcanism and earth quakes) and solar change (luminosity and emissions) and GCR (Galactic Cosmic Ray Events).
In order to reconcile this apparent cessation of warming one has to reach the conclusion that either there are either unknown strongly negative climate forcing factors or that known negative forcing factors have been significantly underestimated or that solar irradiation and GCR plays a very important part.
Saved by the aerosols
Fairly recently, Bellouin et al (2005)(13) have provided the best measurement to date of aerosol direct radiative forcing of -1.9 +/- 0.3 W/m^-2 . In 1997, Hansen et al (14) concluded that there was potentially a missing climate forcing of up to -1 W/m^-2 due to indirect aerosol effects on clouds. The combined effect of these two factors alone is sufficient to offset positive forcing as defined by the IPCC (15) previously ascribed to CO2 but suggested by others to be partially (40% ) (16) or exclusively or predominantly due to aircraft contrails (9).
There is a large body of evidence to suggest that atmospheric aerosols both sulphate and mineral and stratospheric particles, both capable of negative climate forcing (17-29 ), are on the increase (30,31) and make a highly statistically significant difference to cloud droplet number concentrations(32). Indeed nearly all today's clouds are shaped by the effects of human perturbation (33). Further there is a body of evidence to suggest that subsonic aircraft operating at normal cruise altitudes below the tropo-pause inject sulphate aerosol up to 3 km into the stratosphere (34-37) . Further this injection increases non-linearly with fuel sulphur content (38-42). It would thus seem bizarre then that Belloiun et al (2005) claims that aerosols are in decline (43). On the other hand Susan Soloman (2012)(44) working at NOAA, the very same organisation which employs one of Belloiun's co-workers claimed that aerosols were on the increase and that recent measurements demonstrate this but that the “background” stratospheric aerosol layer is persistently variable rather than constant, even in the absence of major volcanic eruptions. Several independent data sets also show that stratospheric aerosols have increased in abundance since 2000 (45,46 ). Soloman further states that near-global satellite aerosol data imply a negative radiative forcing due to stratospheric aerosol changes over this period of about –0.1 watt per square meter, reducing the recent global warming that would otherwise have occurred. Observations from earlier periods are limited but suggest an additional negative radiative forcing of about –0.1 watt per square meter from 1960 to 1990. Further climate model projections neglecting these changes would continue to overestimate the radiative forcing and global warming in coming decades if these aerosols remain present at current values or increase.
Do aerosols have a downside?
It is thought that aerosols might impact on the world's hydrological cycles (47). Hydrological changes have been mentioned elsewhere in connection with persistent aircraft contrails both by the present author (48) and others (49) and here may lay the association.
Other aerosol mechanisms
Aerosols also change the global atmospheric electric current (50,51) and hence the two way propagation of acoustic gravity waves (52-55). The present author has commented on these effects elsewhere (48).
Our understanding of longer term (tens of years plus) planetary/weather cycles is fairly limited (56,57). There is however more than just anecdotal evidence for their existence. Britain has just experienced its coldest Winter and Spring period since 1947. Apparently from the available records the summer of 1947 was the fifth hottest ever on record (58,59) and yet normal seasonal temperatures were not experienced until the last week in May and first week in June. 1963 had a winter followed by an early summer period with similar trends (58-60). Here in Britain in 2013 we are now experiencing a similar recovery of temperature. One cannot perhaps but help ponder on the strength of natural cycles outweighing anthropogenic influence.
Conclusions and further work
Given our present love of flying and international travel and overseas holidays aerosols inadvertently injected from passenger aircraft will, presumably, continue to increase. All aerosols are predicted to grow in numbers until at least 2040 , see Wolf and Hidy 1997 (61).
Our agricultural practices are also estimated to provide between 30-50 % of the dust required for aerosol nucleation above the Atlantic ocean, Abbatt et al (62). Since progressively more land is being turned over to agriculture, wind lofted particles here also provide another increasing source of aerosol, see Miller and Tigen (63). Natural salt spray over the oceans provides most natural sulphate aerosol , see Jacobson 2001 (64) but this is probably being modified as shipping increases, see Hooper and James (65) and ship tracks (66) will require quantification and investigation. Space flight and decaying space junk also significantly adds to particulate matter in the stratosphere (67).
The last two solar cycles have been weaker than for some time (68,69) and the next one is predicted to be minuscule (70). During the Maunder minimum average global temperatures fell particularly in the Northern Hemisphere where the fall was probably between 1 and 2 Celsius (71). Such a fall in global temperatures would impact more severely on modern agriculture than a .5 degree rise (72).
It is imperative that climate scientists take all the present work and its references into account in and in proper context before deciding if geo- engineering climate mitigation will ever be required.
Based on the above premise that aerosols appear to have a far stronger negative forcing effect on climate than previously thought and spreading contrails and contrail cirrus a far stronger positive forcing effect (see O Boucher - Nature Climate Change, 2011 - nature.com) and despite the claims of some, particularly sulphate aerosol appears to be continuing to increase, coupled with the prediction that the next solar cycle could be extremely weak, it is the personal and present view of the present author that geo-engineering should not presently be used. On the plus side, if stratospheric experiments were tested, aerosol residency is measured in days or months (73) rather than several years as with CO2 in the stratosphere (74) or some five hundred years in the atmosphere as a whole before equilibration with the sea (75), see Craig 1957, so any experimentation (should it ever be granted) would if it went wrong only produce transient changes of similar duration. A great fear of its use is inducing either runaway cooling or excessive dimming which could severely sicken the world's agriculture and population. A greater fear is with the use of ocean iron seeding for in addition to phytoplankton being a known CO2 sink, they are also thought to control marine aerosols (76,77), a continued unchecked or increasing production of which could eventually induce either runaway cooling or excessive dimming which could severely sicken the world's agriculture and population.
Whereas at least for the moment the available climate figures seem to tell us that global warming has halted. The author believes it would be premature for the air fleet to switch to ultra low sulphur fuel as this could tip the balance back to warming by reducing sulphate aerosol loading of the UTLS and encouraging spreading contrails. Coincidentally, it would seem very recently indeed that the UK Met Office has considerably revised down its estimate for the warming produced by line shaped contrails, see Forster et al 2010 (78). Contrail avoidance technologies may help cut warming in future, see Noppel and Singh 2007 (79). Such technologies are now being developed and employed even for use in the presence of cross winds at various places in the world, see Sridhar et al 2011 (80). It is somewhat speculative but given the tremendous
impact of air traffic on our climate one wonders if contrail avoidance alone has helped with the recent cooling trends? Certainly at the author's residence the number of days in a year where persistent spreading contrails are observed does seem to have fallen significantly since its peak in about 2005.
What seems certain to the present author is that scientifically applied use of normal air fleet aircraft technology alone viz a viz engine design, fuel components, flight path and routing ought to be sufficient to control (geo-engineer) climate until at least 2040 based on present predictions. As the present author has stated elsewhere it is known that there are also inadvertent local weather changes associated with contrails in particular and as science better also comes to understand these regular contrail weather engineering distinct from or in association with separate techniques such as seeding might become the norm.
Provided of course no materials are employed which injure populations below.
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