Wednesday, September 28, 2011

Global warming might save us

kw: observations, global warming, sunspots, ice ages

This graph, from Wikimedia Commons, is one of the most striking compilations of long-term observations to be had. The blue line charts more than 260 years of sunspot observations gathered since daily observation of the sun began in 1749. The red symbols add less regular observations that stretch back to the time of Galileo.
The most prominent feature is the regular 11-year solar cycle, followed by the significant variations in the height of the solar maximum with each cycle. The Maunder Minimum, a 40-year period in which three solar cycles passed with nearly no sunspots, coincides with the first, and coldest, phase of the Little Ice Age from 1650-1880.

There is not exact correspondence between sunspot activity and climatic heating or cooling. Solar Cycle 4, the beginning of the Dalton Minimum, lags just a little the significant cooling episode that caused the Continental Army under George Washington such suffering during the Revolutionary War. Many of our weather proverbs relate to late LIA conditions in New England. In particular, the old saw about the groundhog's shadow on Feb 2, which originated in Massachusetts in the mid-1800's, is quite a bit out of date. Clear conditions in midwinter no longer foretell a coming cold spell nearly so accurately. We are now in the midst of, or perhaps near the end of, the Modern Maximum which began with Cycle 18 about the time I was born.

The next image, also from Wikimedia Commons, shows recent cycles in more detail, plus predictions for cycle 24, which began in 2010 rather than 2007 as predicted, and 25, which is sheer speculation at this point.
The prediction for Cycle 24 is lower now. Cycle 23 peaked at around 135, while the prediction in the image below, from, shows a prediction of about 90. That matches the range of sunspots during the early 1900's, and it was based upon those that predictions of a cooling episode were made in the 1960s, before the MMax became clear. It is not stated where the very low prediction for Cycle 25 arises, but if 24 is 90 or lower, and 25 is similar, we'll have significant cooling by the year 2030.

One feature of this chart deserves discussion. The curves go below zero! This is because sunspot number was correlated with f0F2 several decades ago, and now "official" sunspot number is taken indirectly. The f0F2 parameter refers to the critical frequency of reflection for the F2 layer in the ionosphere, measured by HF radar. Ham operators occasionally hear loud clicks in various HF bands (3-30 MHz) around sunrise, midday and sunset, caused by the radar measurements, which take only a few seconds. Since the correlation is not perfect, some measurements of critical frequency "figure out" to a sunspot number below zero. I have not located actual sunspot counts for recent years with which to compare this graph.

A lot is riding on the actual magnitude of Cycle 24. It could fool us; there is a lot we still don't know about solar dynamics. We have hardly a clue as to the cause of the Maunder Minimum. What we do know is that, although sunspots are cooler than the rest of the solar disk, the rest of the disk runs a little hotter on average, so that a strong cycle like Cycle 19 might have 1-2% greater sunlight hitting Earth than occurs during a solar minimum such as 2008 or 1995. Averaged out over twenty years or so, the reduced sunlight from a couple of weak cycles can make for stronger ENSO episodes (El NiƱo-Southern Oscillation) and deeper winters. A single year does not show such trends clearly, but decadal averages can. We'll have to wait and see.

In the meantime, let us consider the Medieval Climate Optimum, the period of 500-600 years before the LIA, during which global temperature was probably at least 2-3°C warmer than the decade of 2001-2010. Crops flourished and it was a time of prosperity. Global warming could drive us not just to that point, but beyond it. However, if we have a couple of weak solar cycles, the warming will likely be largely offset. Whether this is seen as coincidence or divine providence, it appears at first blush that we're going to have a postponement of the full effect of global warming, giving us time to increase the efficiency with which we use energy, perhaps even moving our transportation habits back to cars with Model A performance (they'd go 50-60 mph or 80-100 kph, but with 20HP, took a while to get there). That's what it will take to approach 100 mpg/160 kpg.

The other side of the coin is that, without global warming, we could have another series of winters such as those of the 1780's. Imagine postponing your Easter Egg hunt until the snow melts, or wearing your flannel underwear from September to April or May (add six months to these if you're in South America or Australasia). I like cold weather, but it has its limits. I have lived in South Dakota, and having SD conditions in PA would take some getting used to, such as putting our water main deeper underground where it couldn't freeze. A little global warming might just be our best friend!

No comments: