BLOGS

Figure 1. The Vadret da Tschierva glacier in 1935 (top) and in 2022 (bottom).Photos courtesy of swisstopo, L. Hösli, G. Carcanade, M. Huss, VAW-ETHZ.

Topics: Civilization, Climate Change, Fluid Mechanics, Global Warming, Meteorology, Research

Glaciers—dynamic masses of ice descending from the mountain tops—have always been fascinating to humankind. They intrinsically belong to the high-alpine environment. Countless photographs immortalize their bright white beauty and the power they radiate. Glaciers have been depicted on oil and parchment for centuries, as if trying to capture their transience. They are constantly moving; under the influence of gravity, the ice generated at high elevation flows downwards and shapes tremendous glacier tongues that are speckled with deep fissures known as crevasses. Sometimes, the openings to these crevasses are hidden by a light dusting of snow; subsequently, mountaineers need a lot of experience to accurately judge their exposure to the ice.

Even though glaciers are not living things, they are not lifeless. For many mountain regions worldwide, glaciers function similarly to lungs: They absorb snow in wintertime and “breathe” out water during hot summer days. This glacier water is urgently needed, especially in dry periods.

Glaciers consequently have a relevance that goes far beyond the mountain peaks where they reside. A reduction in meltwater from glaciers would be painful for nature and the global economy: irrigation of fields would be restricted, the temperature and mineralization of rivers would change, and during periods of drought, serious bottlenecks could come into existence for the drinking water supply and for shipping on rivers. In addition, melting glacial ice contributes to sea-level rise and therefore directly or indirectly affects billions of people living near the coast.

Despite, or perhaps because of, their majestic appearance, glaciers can also pose an immediate threat. Glaciers can produce floods and ice avalanches that endanger villages in the valleys. Together with permafrost, glaciers also stabilize mountain flanks and therefore reduce the potential for rock falls and landslides—a role that is becoming increasingly lost.

The so-called “eternal” ice of glaciers tells a long and dynamic story. During the Ice Age, ice sheets covered a large part of the North American continent, as well as Europe. The last time this happened was around 20,000 years ago—a blink of the eye from a geological perspective. Since then, the climate has changed, due both to natural factors and to anthropogenic influences—human-caused factors—which have massively accelerated over the past 100 years (Marzeion et al., 2014). As a result, the glaciers are still present, but they are getting smaller every year.

The Alps’ iconic glaciers are melting, but there’s still time to save (most of) the biggest, Matthias Huss, Bulletin of the Atomic Scientists.

Observations of clouds, sunbeams, and birds—like those seen in this photo taken in Salisbury, UK—were important elements of classical weather forecasting. (Image courtesy of Peter Lawrence.)

Topics: History, Meteorology, Research

In August 1861 the London-based newspaper The Times published the world’s first “daily weather forecast.” The term itself was created by the enterprising meteorologist Robert FitzRoy, who wanted to distance his work from astrological “prognostications.” That story has led to a widespread assumption that weather forecasting is an entirely modern phenomenon and that in earlier periods only quackery or folklore-based weather signs were available.

However, more recent research has demonstrated that astronomers and astrologers in the medieval Islamic world drew widely on Greek, Indian, Persian, and Roman knowledge to create a new science termed astrometeorology. Central to the new science was the universal belief that the planets and their movements around Earth affected atmospheric conditions and weather. It was enthusiastically received in Christian Latin Europe and was further developed by Tycho Brahe, Johannes Kepler, and other astronomers. The drive to produce reliable weather forecasts led scientists to believe that astrometeorological forecasting could be more accurate if they used precise observations and records of weather to refine predictions for specific localities. Such records were kept across Europe beginning in the 13th century and were correlated with astronomical data, which paved the way for the data-driven forecasts produced by FitzRoy.¹

Islamicate astrometeorologists were the first to replace the ancient practice of observing only short-term signs, such as clouds and the flight of birds, to predict the weather. They based their action on the hypothesis that weather is caused by the movements of planets and mediated by regional and seasonal climate conditions. Improved calculations of planetary orbits and updated geographical and meteorological information made the new science possible and compelling.

The prospect of acquiring reliable weather forecasts, closely linked to predictions of coming trends in human health and agricultural production, made the new meteorology attractive in Christian Europe too. Considerable pride shines through medieval Christian accounts of the weather questions that they could now start to answer. Central among them was one that classical meteorologists had failed to figure out: How can weather vary so much from one year to the next when the seasons are caused by regular, repeating patterns produced by Earth’s spherical shape and its interactions with the Sun?

Medieval weather prediction, Anne Lawrence-Mathers is a professor of history at the University of Reading in the UK. Physics Today