Penitentes are a snow formation found at high altitudes. They take the form of tall thin blades of hardened snow or ice closely spaced with the blades oriented towards the general direction of the sun. Penitentes can be as tall as a person.

Penitentes were first described in the literature by Darwin in 1839. On March 22, 1835, he had to squeeze his way through snowfields covered in penitentes near the Piuquenes Pass, on the way from Santiago de Chile to the Argentinean city of Mendoza, and reported the local belief (continuing to the present day) that they were formed by the strong winds of the Andes. These pinnacles of snow or ice grow over all glaciated and snow covered areas in the Dry Andes above 4,000 m (Lliboutry 1954a, Lliboutry 1954b, Lliboutry 1965). They range in size from a few cm to over five meters. (Lliboutry 1965, Naruse and Leiva 1997).

Lliboutry noted that the key climatic condition for the differential ablation that leads to the formation of penitentes is that dew point is always below freezing. Thus, snow will sublimate, which requires higher energy input than melting. Once the process of differential ablation starts, the surface geometry of the evolving penitente produces a positive feedback mechanism, and radiation is trapped by multiple reflections between the walls. The hollows become almost a black body for radiation, while decreased wind leads to air saturation, increasing dew point temperature and the onset of melting. In this way peaks, where mass loss is only due to sublimation, will remain, as well as the steep walls, which intercept only a minimum of solar radiation. In the troughs ablation is enhanced, leading to a downward growth of penitentes.

Recent studies indicate that most of the South American glaciers are drastically reducing their volume at an accelerated rate and could even dis-appear in the next few decades.
By Gino Casassa

Southern South America accounts for about 65 percent of all Andean glaciers. The main areas in this region are the northern Patagonia Icefield with an area of 4,200 km2, the southern Patagonia Icefield with an area of 13,000 km2, and Cordillera Darwin with an area of 2,000 km2. These icefields contain the largest glaciers in the southern hemisphere outside of Antarctica, and are a potentially invaluable source of present and past environmental information from the mid-latitudes, providing a link between the southern tropical and equatorial regions and Antarctica.

There are currently many examples of drastic glacier retreat within the southern South American icefields. O’Higgins Glacier has retreated 15 kilometers during the last century in what is probably the largest retreat in all of South America. A recent thinning of 14 meters a year has been measured at Upsala Glacier, and a record thinning of 28 meters a year has been detected at HPS 12 Glacier in Falcon fjord.

Glaciers of all the South American Andes, including the tropical and equatorial regions, cover a total area of 31,000 km2. Although they store an equivalent global sea level rise of only a few centimeters if they were to melt completely – which represents much less than ten percent of the total volume of mountain glaciers of the world – they are presently contributing more than ten percent of total global sea level rise from mountain glaciers.
Glaciers have a critical importance for the water resources in the region, and are of great significance to mining, tourism and agriculture. There have also been numerous incidents of catastrophic glacier floods and mudflows originating from glacier melt due to volcanic eruptions, which have affected human activities and settlements, causing several tens of thousands of casualties, such as in Nevado del Ruiz, Colombia, the Cordillera Blanca in Peru, east of Mendoza, Argentina, and at the Copiapó River, the Villarrica Volcano and the Paine National Park in Chile.

The Chacaltaya glacier in Bolivia, which provides water resources to the City of La Paz, is predicted to melt completely within the next 15 years if the present atmospheric warming trend continues into the future. The incidence and speed of glacial retreat has generally accelerated during the last decades, and hundreds of years old glaciers will collapse within our own lifetime.

The global picture for Andean glaciers

Although a few glaciers around the world are advancing and increasing in volume – in response to increased local precipitation, such as in New Zealand and Norway – there is an overall tendency for retreat and thinning as a result of the global climate warming observed during the last one and a half centuries, since the so-called Little Ice Age, the last cold period which affected the Earth during 1400-1900 AD.
A direct effect of glacier retreat is sea level rise. The water frozen in all the glaciers of the world, mainly in the ice sheets of Antarctica and Greenland, but also in South American glaciers on the retreat smaller ice caps and glaciers, would be sufficient to raise sea level by 70 meters at a global level. Global sea level is presently rising by nearly 2 millimeters per year, partly due to glacier melt.

Signs of recent glacier wastage have been detected in the ice sheets of Greenland and Antarctica, and also in many of the earth’s mountain ranges, including Africa, the European Alps, the Himalayas, Alaska and the Andes. In spite of important studies carried out on South American glaciers by European, North American, Japanese, and South American scientists, many basic scientific issues concerning the present and past glaciations in South America and their relation to climate are yet to be explored and studied. Moreover, the potential impact of the retreat of glaciers on the environment and human activities has yet to be adequately assessed.

Climate change needs to be better understood

The climate is undergoing drastic changes on a global scale, with clear evidence of recent warming. In nine of the last twelve years, the mean global average temperature has been higher than at any time since the start of historical records at the beginning of the 19th century.
The mean global temperature during the 1990s is probably the warmest of the last 1,000 years according to records, and the extreme heat which affected Europe this summer is not running counter to the trend: temperatures were recorded at five to ten degrees higher than normal, in several cases exceeding 40ºC. There is a general consensus within the scientific community that global warming is at least partly due to the enhanced greenhouse effect as a result of the burning of fossil fuels since the Industrial Revolution.
It is not clear yet how much of this warming is attributable to anthropogenic greenhouse gases as compared to warming due to natural climate variability since the Little Ice Age. The role of natural solar variability in global warming is also not clear. There is high priority in resolving these issues, especially considering ongoing international efforts to limit the emission of greenhouse gases, in particular the ratification of the Kyoto Protocol. Continued research on the world’s glaciers – including those of South America – will contribute important knowledge for understanding why, how and how quickly our global climate is changing.

By now most people have heard of El Niño, if only to know the name refers to some kinds of abnormal weather. The definition of "abnormal" varies widely with geography, though. For people who live in Indonesia, Australia, or southeastern Africa, El Niño can mean severe droughts and deadly forest fires. Ecuadorians, Peruvians, or Californians, on the other hand, associate it with lashing rainstorms that can trigger devastating floods and mudslides. Severe El Niño events have resulted in a few thousand deaths worldwide, left thousands of people homeless, and caused billions of dollars in damage. Yet residents on the northeastern seaboard of the United States can credit El Niño with milder-than-normal winters (and lower heating bills) and relatively benign hurricane seasons

Originally, the name El Niño (Spanish for "the Christ child") was coined in the late 1800s by fishermen along the coast of Peru to refer to a seasonal invasion of warm southward ocean current that displaced the north-flowing cold current in which they normally fished; typically this would happen around Christmas. Today, the term no longer refers to the local seasonal current shift but to part of a phenomenon known as El Niño-Southern Oscillation (ENSO), a continual but irregular cycle of shifts in ocean and atmospheric conditions that affect the globe.
El Niño has come to refer to the more pronounced weather effects associated with anomalously warm sea surface temperatures interacting with the air above it in the eastern and central Pacific Ocean. Its counterpart—effects associated with colder-than-usual sea surface temperatures in the region—was labeled "La Niña" (or "little girl") as recently as 1985.

The shift from El Niño conditions to La Niña and back again takes about four years. Understanding this irregular oscillation and its consequences for global climate has become possible only in recent decades as scientists began to unravel the intricate relationship between ocean and atmosphere. Although meteorologists have long been forecasting daily weather based on atmospheric measurements taken around the world, they had relatively little information about conditions in many parts of the world’s oceans until the advent of arrays of fixed unmanned midocean buoys in the Pacific Ocean and orbiting satellites.

But technological advances were not the only key. As the following article recounts, atmospheric and oceanographic researchers, after years of independent inquiry into the basic workings of air and sea, at last joined forces. An elegant synthesis of these two fields of research now enables climatologists and oceanographers to construct theoretical models to simulate and predict the broad climate changes associated with ENSO.
For example, scientists can now warn vulnerable populations of an impending El Niño event several months in advance, providing precious time in which to take steps to mitigate its worst effects. Invaluable as this prediction of El Niño is, it is just the first step toward the much longer-term goal of providing the climatic counterpart to the daily weather prediction that we have come to take for granted.