This article appeared in the Summer, 1997 issue of New Mexico Resources.
While old-timers scratch their heads to prompt memories of decades past, Curtis Monger digs deep into the desert soil to prod memories of 700 millennia.
Around the world, weather records are most often gathered from core samples of deep ice and tree rings, both in short supply in the Chihuahuan Desert studied by Monger, soil scientist with NMSU's Agricultural Experiment Station. So he mines fossils of microscopic pollen and isotopes in caliche from trenches in southern New Mexico, Mexico, and Big Bend, Texas.
These fossils will never catch attention in a museum display, but they are painting a picture of the ice age in southern New Mexico that alters some botanists' visions.
"The Chihuahuan Desert was much more of a grassland than forest during the ice age," Monger says. "Depictions of our desert as forested in the ice age are based on evidence from pack rat dens."
But pack rats, Monger says, left their botanical cache around the Chihuahuan region in cliff-side dens that were at higher elevations, where more trees exist even today. Some of today's barren mountains probably were forested, while lowlands were grass, based on Monger's pollen fossils and soil isotopes, which were distributed evenly in the Chihuahuan basins.
That ice age in the Chihuahuan region would have been very nice sweater weather (or light hide weather for the inhabitants in those days), Monger says. The Chihuahua was characterized by many large lakes in what is now dry rangeland.
The world is now in the latest 10,000- to 20,000-year interlude between longer 100,000-year-long ice ages, which geologic evidence shows to be part of a regular cycle. The warming and drying in this period in the Chihuahuan region peaked some 8,000 years ago, making the region a true desert with grasslands giving way to shrubs as part of a natural desertification process. After that, grasses began to recover as the weather trend turned toward the next ice age.
Humans were in the region at least 11,000 years ago, Monger says, but it wasn't until some 3,000 to 4,000 years ago that people first experimented with agriculture. By that time, corn had made its way up from Mexico as a domesticated crop, before spreading across the continent. Not until 2,000 years ago did agriculture appear to be a serious undertaking in the region.
When Europeans entered the region, grass was the major lowlands plant. Humans made their mark on the poor, sandy soil portions of the area. From digs, clearly many of these areas, often characterized by mounds of sand, were once flatlands.
"But it is important to point out that negative human impact was spotty," Monger says. "Where soils hold water, like in playa lakes, there is no discernible impact from humans."
In the long term, there is greater environmental concern. The earth may be taking a dramatic departure from its regular on-off cycle for ice ages. Carbon dioxide, the major element that traps earth-warming solar radiation in the atmosphere, has been measured in air trapped in glacial ice. Its levels shadowed the slow, regular ice age cycle closely until now. Usually the levels vary from 200 to 300 parts per million in the atmosphere, between the peak of ice ages and the peak of the warm interludes.
Such a swing normally took thousands of years. Yet the same 100-parts-per-million swing occurred from 1957 to the early 1990s, ranging from 260 to an off-the-chart 360.
A hope remains that this is a statistical aberration, which is an artifact of measurement. After all, the measurements from this century were not taken from bubbles trapped in ice. If it is a true comparison, however, the implication is that the world may be headed for weather unprecedented in the last 40,000 years. Within a couple of generations, big changes in sea current temperatures, higher sea levels, and unusual turns in weather patterns could be in store.
Beyond that, the mere increased presence of carbon dioxide appears to fertilize shrubs, putting them at a competitive advantage over grasses that most people associate with desirable rangelands. Monger cautions that predicting what New Mexico will be like in two or 20 generations isn't possible. He notes that if current global weather models had been used in 1920 to forecast today's climate, they would have exaggerated the effects of carbon dioxide.
"The science isn't there yet," Monger says. But he's excited to be part of the process of getting it there.