The latest Accretionary Wedge, the acclaimed gathering of the Geoblogosphere, is hosted this time by Geologist Ron Schott at his "Geology Home Companion Blog" and he is asking for "the most memorable or significant geological event that you've directly experienced."

If a geologist claims to have directly experienced a geological event there are only two possible explanations: the event happens extraordinarily fast or the geologist is very, very old.

In 1859 the British physicist John Tyndall discovered the importance of CO2 and water vapour for the temperature balance in earth's atmosphere. In 1896 the Swedish scientist Svante Arrhenius calculated the variations of temperature for different concentrations of CO2, observing that the emissions of the industry of this gas could modify the atmosphere and the climate.

In 1938 the first measurements in the Polar Regions showed an increase in the measured temperature and since 1979 the scientific community is actively warning of the influence of humankind on the global climate (The New York Times has an exhaustive timeline of Science and Politics of Climate Change).

If we compressed earth's history in one year, these 150 years would be approximately one second and still more than double an average human lifespan. It therefore could seem that the physics behind anthropogenic global warming is abstract and the effects only perceivable by a human observer in a remote future.

However black and white photos from just two generations ago show us entire valleys covered by a glacier and the glacial retreat has increased in speed in the last decades. Now even a young geologist can report the disappearance of glaciers and the actual environmental and climate change as first hand experience - a memorable, but also alarming experience.

Fig.1. & Fig.2. Two alpine glaciers at the beginning of the 20th century and in the early 21st century (image in public domain).