Utter the phrase "global warming" in polite conversation, and you may hear reactions ranging from "it's all a plot by the environmentalists to take away our SUVs!" to "the oceans are rising, we're all going to drown!" Some are convinced that the measured increase in temperatures over the last century are a result of human activity - mostly conversion of fossil fuels to atmospheric carbon dioxide. Others will argue that the 1° C temperature rise is smaller than variations which occur naturally and have been measured by observing ice cores and tree rings going back several thousand years. Part of the problem in interpreting the data is that small changes in the global mean temperature are often accompanied by larger local variations, some of which actually result in lower temperatures for some regions.
Recent work, reported in the December 7 issue of Science, suggests a connection between variable solar radiation and long-range climate fluctuations. Analyzing existing records and proxy data (indirect measurements from tree rings, ice cores, coral growth, etc.) researchers have correlated an extended period of low solar irradiance in the 17th and 18th centuries with an extended spell of cold weather in Europe and North America. Part of this corresponds with a period of unusually sparse sunspot activity known as the Maunder Minimum. The connections are not completely intuitive - high sunspot activity is actually correlated with more sunlight, since the dark spots are accompanied by brighter, hotter regions known as plages. The plages contribute more than the sunspots subtract, so a dearth of sunspots means less sunlight to warm the Earth.
The real surprise is that even small changes can trigger large departures from the equilibrium temperature. That's part of the concern about human activity - we're shifting the baseline just a little, but the consequences could be far out of proportion because of the sensitivity of the system. The reported recent temperature rise is in addition to the normal 11-year cycle of solar activity, but some of our recent warm years are most likely explained by the recently passed solar maximum, when sunspot activity was at its 11-year high.
In the same issue of Science we find a Martian connection to this notion. Data gathered by the Mars Global Surveyor indicate that Mars has warmed slightly over the 2 years of observations. Most striking is the Martian year-to-year retreat of the southern polar cap. These polar caps are composed of solid carbon dioxide (dry ice), which sublimates in summer - passing directly from solid to gas - and freezes out of the atmosphere in winter. The depth of the seasonally varying part of the caps is on the order of a few meters to a few tens of meters. The southern polar cap displays unique circular pits and mesas, and the edges of these features appear to have retreated an average of 3 meters over the time of the observations. This corresponds to the release into the atmosphere of some 1013 kilograms of CO2. If the release of this greenhouse gas continues over many Martian years, the atmosphere will become both warmer and denser, which will cause even more sublimation. The planet could warm dramatically in a century or so … as could Earth, if we don't stop releasing greenhouse gasses into our own atmosphere!
Lunar Phases for January: Third Quarter on the 5th; New Moon on the 13th; First Quarter on the 21st; Full Moon on the 28th.
Jupiter will be at opposition on the 1st - it will rise in the northwest at sunset and be visible all night. Saturn is above and to the right, with Mars high to the south early in the month, settling towards the west near the end. Mercury is visible after sunset, getting higher towards mid-month but disappearing swiftly by the end of the month. Venus will return to the western evening skies late in the month.
An overhead view at mid-month, approximately 8:30 pm finds the Milky Way arching from northwest to southeast. The great square of Pegasus lies to the west, to the left of Mars. Deneb in Cygnus is low on the northwest horizon. Regulus is just coming up to the east - by springtime it will be to the south at this time of evening. Castor and Pollux, the twins in Gemini, are high above the eastern horizon, with Jupiter spending the month in this constellation, above and to the right. The southeast is dominated by Orion, followed by the faithful Dog Star - Sirius. Above Orion we can find Aldebaran, the bright eye of the Bull in Taurus, with Saturn close by for the month.
George F. Spagna, Jr.