Hotter Now than Ever?
Paleoclimatologists have used proxy data (tree rings, ice cores, and so on) to reconstruct the Earths climate in the distant past. Many remarkable discoveries have been made, including the fact that climate has changed dramatically and rapidly in the past due entirely to natural causes. Others are claiming, however, that this evidence shows that the current warm period is human-induced.
Jonathan Overpeck, head of the paleoclimatology program for the National Oceanic and Atmospheric Administration, told an audience at a meeting of the American Geophysical Union in San Fransisco, that the earth is warmer now than it has been in the last 1,200 years. “There is no period that we can recognize in the last 1,200 years that was as warm on a global basis,” said Overpack. “That makes what were now seeing more unusual, and more difficult to explain without turning to a greenhouse gas mechanism.”
“Not only,” said Overpack, “has the 20th century produced the hottest years on record but the magnitude of change appears to be without parallel since at least 800 A.D.” Overpack also addressed the issue of the dramatic warming of the Middle Ages, known as the Medieval Warm Period, which has been used as an historic example of dramatic natural climate change. Overpack claims that it never happened. He argues that “the thaw appears to have been limited to northern latitudes in Europe and North America, while other parts of the globe saw little change in temperature” (Washington Post, December 8, 1998).
Overpacks argument is specious, however. He claims that the temperature changes of this century are global, but this is untrue. Patrick Michaels, a climatologist at the University of Virginia, has pointed out that the small amount of surface warming over the last century has been largely confined to the northern latitudes of America and Siberia. The rest of the globe has remained mostly unchanged, similar to the Medieval Warm Period. This, of course, raises global average temperatures but so did it in the Middle Ages.
How Widespread are El Nios Effects?
This last year has seen the rise of El Nios fame. Many of 1998s notable weather events were generally linked to El Nio in the press. This may have given the public the impression that El Nio has more influence on the worlds climate system than is warranted. The September issue of the International Journal of Climatology addresses the issue of El Nio/La Nia impacts.
The study looked at El Nios impact (thought to be significant) on the South Pacific by studying upper atmospheric winds for three major La Nias and four El Nios since 1975. They found, “a considerable deal of inter-cold and warm event variability in the propagation of height and temperature anomaly patterns [such that] clear and unequivocal propagation signals common to all cold and warm events are not revealed. This is because the anomaly movement is rarely consistent from one warm (cold) event to another, especially in the subtropical to subpolar latitudinal range.”
Commenting on the study, the World Climate Report explains, “outside of the tropics, the impact from every El Nio or La Nia event differs. There is no compelling evidence that El Nios are becoming more common . . . .[or] are linked to global warming. In short , El Nios are like all other climate events unpredictable” (www.nhes.com).
El Nio and Temperature Change
The link between global warming and El Nio has not yet been made, but this has not stopped global warming activists from connecting the two phenomena. John Daly has taken a look at the satellite temperature data and the southern oscillation index (SOI), “an index number derived by comparing air pressure at sea level between Darwin and Tahiti. During an El Nio episode, the index becomes a negative number, and is characterized by warming of the central and eastern Pacific Ocean . . . . During a La Nia episode, the reverse happens and a cooling takes place.” By comparing the two sets of data it is easy to see that there is a cause and effect relationship between temperature and the SOI, but it is the El Nio/La Nia cycle that effects temperature and not the other way around.
The data show that “global temperature lags the SOI by between 6 and 9 months,” says Daly. “It is clear that the Southern Oscillation is the causative agent. An effect can only follow a cause, it cannot precede it, and so there is no dispute here about what the chain of cause and effect must be.
Daly argues that, “based on the the assumption that the Southern Oscillation is the primary driver of year-to-year global temperature, with a 6 to 9 month lag time, we can now predict that since the SOI has now gone sharply into La Nia mode in the last 6 months, global temperature will follow (with the predicted time lag) and fall to below the zero line (the long term average of temperature) in the next few months. The latest monthly value for temperature was +0.33C in October 1998, after reaching a peak of +0.72C in April. Since the SOI moved into La Nia mode in June, we can expect global temperature to fall below the zero line by March 1999.”
Commenting on the claim that manmade carbon emissions is the cause of El Nio Day says, “The Greenhouse industry readily blames greenhouse gases, but the idea that a few parts per million of CO2 can cause the overturning of trillions of megatonnes of sea water is fanciful to say the least, a reasoning based more on ideology than on science. Those who point to greenhouse gases as the cause of El Nio fail to describe exactly what mechanism they imagine the gases to be performing to achieve such a feat” (www.vision.net.au/~daly/soi-temp.htm).