Life in the Rear-view Mirror

Another Ice Age or Continued Global Warming?

The scientific record going back to more than half a million years shows that the earth has seen many ice ages. They happened with regularity: about one every one hundred thousand years. They are associated with the eccentricity of the earth's orbit, which changes every one hundred thousand years from circular to elliptical. This change of eccentricity is known as the Milankovitch cycle, named after the scientist that discovered it. Based on the evidence of the past half million years, until recently scientists believed that we were on the verge of another ice age. Rising CO2 levels, well beyond what was seen in the past, has some scientists questioning that.

It's only the last ten thousand years that the northern hemisphere has experienced relatively warm temperatures. The typical climate cycle has global temperatures rising for about twenty thousand years and then dropping for about eighty thousand. This short period, in between ice ages is referred to as the interglacial period. With some luck, rising levels of CO2 may push out the start of the next ice age, giving us a respite from impending colder temperatures.

The temperatures, which are inferred from pollen measurements in ice cores, don't go straight up and straight down. There are many ups and downs within the rising and falling trends. There are two more Milankovitch cycles that affect the ups and downs. One is due to the earth's axial tilt, which varies from about 21.5 to 24.5 degrees, and has a period of 41,000 years. The other is due to the earth's precession. The earth's orbital plane changes every 26,000 years and causes the North Star to change from Polaris (currently) to Vega, in the future.

In addition to the three Milankovitch cycles, which affect the larger structure of the temperature graph, there are the sun's own magnetic storms that affect the fine structure.

In the last 35 years, for which solar irradiation has been accurately measured by satellites, there have been three solar minima in 1987, 1997, and 2009. The period is about 11 years and the variations are very small, ranging from 1360 to 1364 Watts per square metre. The peaks occurred in 1990, 2000, and in 2013 - each peak being lower than its predecessor. They are driven by sunspot activity. Interestingly, between 1650 and 1700 there was very little sunspot activity, and that period is known as the Maunder Minimum.

The reason why very small changes in solar irradiation have a significant impact on climate is the ultraviolet component, which creates ozone in the stratosphere. Ozone helps to warm the stratosphere, particularly above the tropics, enhancing the wind currents in the stratosphere and the mass exchange with the troposphere. In effect, the ultraviolet rays help to amplify the very small changes in solar radiation that occur during sunspot cycles.

Sunspots are dark regions of the sun, which are much cooler than the rest, created by the sun's magnetic field. However, the same magnetic field creates faculae, which are much brighter than the rest of the sun and more than compensate for the cooler sunspots. As the sunspot number rises or falls, the distribution of energy within the light spectrum changes. High levels of sunspot/facula activity enhance radiation in the ultraviolet and x-ray wavelengths far more than the visible portion of the spectrum. At the peaks of solar activity, ultraviolet and x-ray radiation increase by several percent, whereas total solar irradiation increases only 0.1%. Therefore, it's not the increase in total solar energy that affects climate, but the higher level of ozone produced by the disproportionate increase in ultraviolet and x-ray radiation.

The sun's magnetic field protects the earth from harmful cosmic radiation. When it enters the earth's atmosphere, it produces Carbon-14 and Beryllium-10. The quantities produced are an indication of the sun's magnetic field strength, which is cyclic. Concentrations of C-14 and Be-10 in ice cores examined by scientists vary significantly with time and reveal cycles of 2300, 210, 88, and 11 years. Therefore, climate is also affected with these same frequencies.

The Little Ice Age, which affected the northern hemisphere, particularly Europe, between 1550 and 1850, was marked by rapid expansion of mountain glaciers, especially in the Alps, Norway, Iceland, and Alaska. It could have been caused by any number of the above-mentioned solar factors, but more likely due to changes in the sun's magnetic field strength. All this is to say that, given what we know from past experience, straight-line extrapolations of current global warming trends are fraught with peril.

If the Greenland and West Antarctic ice sheets are melting, shouldn't they cause ocean temperatures to cool? And if ocean temperatures cool, shouldn't air temperatures also cool, or at least moderate the effect of greenhouse gases? Quite possibly, for the next decade or two, we could have a cooling trend!

A major concern of global warmers and climate changers is rising sea levels. A combination of factors, such as: rising ocean surface temperature, increasing ice melt, increasing rain water runoff, and depletion of land aquifers, are causing ocean levels to rise. Between 2000 and 2010, the average increase in ocean level was 30 mm. If the same rate keeps up for the rest of the century, the total increase by 2100 will be 300 mm - about one foot. To put that into perspective, consider the following.

During an ice age, the oceans evaporate water to the atmosphere and the latter deposits it on the landmasses as ice. Throughout the interglacial period, the ice masses melt and the water returns to the oceans, raising their level. Twenty thousand years ago, in the grip of the ice age that covered most of the northern hemisphere, ocean levels were about 120 m below the present; and then they started rising. By simple arithmetic, the ocean level has risen 6 mm per year (120,000 mm/20,000 years), on average. Therefore, the current 3 mm per year increase is well below the average of the last 20,000 years. During the melting of the ice sheets, the rate of rise was much higher - 20 to 30 mm per year. Moreover, before the last ice age began, about 100,000 years ago, ocean levels were 4 to 6 metres above the present ones! Why are we alarmed about a cycle that has been repeating itself for eons?

Another thing, global warmers and climate changers tend to speak of climate as strictly a global phenomenon. It's not!

Climate is also a local and regional phenomenon. We even speak of microclimates, to indicate particular climates affecting only a very small area of the Earth's surface. Moreover, ice ages always occur in the northern hemisphere, where most of the earth's landmass is located. Therefore, the northern hemisphere could be in a deep freeze, while the southern hemisphere could be enjoying balmy weather.

Despite the wealth of scientific information, there is a lot of emotion and irrationality associated with the subject, not to mention fear mongering. At a time when infrastructure is crumbling all over the developed world; millions of people are dying from waterborne diseases because they don't have access to clean water; and world population keeps growing at alarming rates, people are prepared to divert precious resources to CO2 sequestration, or other cockamamie schemes. Slowing population growth and feeding another one billion people within the next decade are by far more pressing problems.