There are two kinds of ice ages; they are fundamentally different and therefore require different methods of mitigation: (i) Major (Milankovich-style) glaciations occur on a 100,000-year time-scale and are controlled astronomically. (ii) Little ice ages were discovered in ice cores; they have been occurring on an approx. 1500-yr cycle and are likely controlled by the Sun. The current cycles cooling phase may be imminent and calls for urgent action.
Major glaciations on a 100,000-year time scale
I recently published an essay on how to avoid the next major ice age; there have been nearly 20 such glaciations in the past two to three million years. The coolings are rather severe: the most recent one, ending only about 12,000 years ago, covered much of North America and Europe with miles-thick continental ice sheets and led to the disappearance of barely surviving bands of Neanderthalers; they were displaced by the more adaptable Homo Sapiens.
According to the Serbian astronomer Milankovich, glaciation timing was controlled by astronomical parameters, such as oscillations with a 100,000-year period of the eccentricity of the Earths elliptic orbit around the Sun; oscillations with a period of 41,000 years of the Earths obliquity (inclination of the spin axis to the orbit plane, currently at around 23 degrees); and a precession of this spin axis, with a period of about 21,000 years.
While many consider the timing issue as settled, there are plenty of scientific puzzles still awaiting solutions: For example, how to explain the suddenness of de-glaciation, transiting within only centuries from a glaciation maximum into a warm Inter-glacial, like the present Holocene period.
Most expect the next glaciation to arrive rather soon; but calculations by Prof Andre Berger of the Catholic University of Louvain, Belgium, suggest a delay of some 40,000 yearsso there may be no great urgency. Nevertheless, it would be useful and of great scientific interest to verify the existence of a hypothesized trigger that might be disabled by human actionat low cost and negligible risk.
Little ice ages (LIA) and the Dansgaard-Oeschger-Bond (D-O-B) cycles
After digesting hundreds of comments about my essay on stopping the next major ice age, I recognized the need to explain the existence also of little ice ages, which are likely of solar origin. They seem to occur quite apart from the major glaciations, have a cycle length of about 1500 years, and demand different methods of mitigation. They were discovered in Greenland ice cores by the Danish researcher Willy Dansgaard and by (Swiss scientist) Hans Oeschger, and further observed in ocean sediments by the late US geologist Gerard Bond [see Unstoppable Global Warming: Every 1500 years, by Singer and Avery, published by Rowman&Littlefield, 2007].
We dont know what triggers an LIA, but suspect a strong correlation with a quiet Sun and prolonged absence of sun spots. Experts in this fieldWillie Soon (Harvard Observatory), Harjit Ahluwalia (University of New Mexico), Russian astronomer Habibullo Abdussamatov, and many othersbelieve that the next LIA is imminent. The most recent LIA lasted from 1400 to 1830 ADoff and on. It followed the Medieval Warm Period (MWP), when wine grapes grew in northern England and Norsemen were able to farm in southern Greenland.
The impact of the LIA was rather severe. Climatology pioneer Hubert Lamb documents crop failures, starvation, and disease in Europe, together with ice fairs on the frozen Thames. During much of the American Revolution, New York Harbor was frozen over. And we recall paintings of George Washington crossing the Delaware River, impeded by ice floes.
How to overcome an LIA
To avoid the huge human misery and economic damage, one would like to counteract the cooling phase of the D-O-B cycle but how? The next LIA may be imminent; but there is no obvious trigger for solar
influence; our understanding of solar physics is limited by the rather short history of observation of the Sun. While data on sunspots go back centuries, modern observations using spacecraft extend only for years.
An obvious scheme to counter a cooling is to make use of greenhouse (GH) warming. However, carbon dioxide is not the answer: CO2 is limited in supply and is already saturatedhence additional CO2 is not very effective. Synthetics, like SF6, are too long-lasting and may have risky side-effects. The answer may be water, but in the form of ice crystals; the scheme is easily tested and is transitoryreversible and incurring little risk.
Here is how I picture the operationstarting with a small feasibility test and validation of the theory:
A KC-135 or similar aerial-refueling aircraft carries ~100 tons of water, which is to be injected as mist just above the tropopause, at the bottom of the stratosphere, near an atmospheric temperature minimum. At a surface density of water mist of 0.1 kg/m2, the area covered would be ~1km2.
Like contrails, I expect some visible cirrus, which should disappear rapidly, leaving behind invisible cirrus ice crystals that are strong absorbers/emitters of infrared (IR) radiation, covering also the atmospheric window region of 8 to 12 micronsthus creating a major GH effect and possibly even some detectable warming at the Earths surface. Any satellite-borne IR-instrument should be able to see this emitter patch and follow its spread and decay.
However, all this is based on theory and calculations, which I published in 1988 in the peer-reviewed journal Meteorology and Atmospheric Physics. Obviously, all predictions must be validated by direct observations. Once the scheme is scientifically verified, operational planning for countering the cooling can take over.
As usual, there are many scientific questions that require answers chiefly, understanding the physical mechanism that drives the D-O-B cycles; how to explain the size, shape, and duration of the abrupt quasi-periodic warmings. Currently, there is a hot dispute about the synchronicity of the cycles between the two polar regions, revolving about the limited accuracy of ice-layer dating in Antarctic cores.
While the science is certainly interesting and important, there is no need to delay the crucial and urgent tests of geo-engineering; they involve only minor costs and little risk to the atmospheric environment.