Quarry workers extracting basalt in 1914 high on Bonn's river bank — opposite the UN’s climate secretariat — found remains of a woman, a man, a dog and their artifacts, all neatly buried. Radiocarbon dating would later show that they had lived 14,000 years ago.

That find in Oberkassel on Bonn’s outskirts was far younger than the famed Neanderthals, 42,000-year-old remains excavated at another quarry near Düsseldorf in 1856 — just three years before Charles Darwin upset creationists by publishing his theory of species evolution.

2009: Researcher Liane Giemsch examines the skeletons

Living 14,000 years ago, Bonn's unnamed homo sapiens couple probably lived in seasonal camps, hunting the likes of deer and beaver, as western Europe emerged from its largely treeless ice phase, known scientifically as the Last Glacial Maximum.

That deep chill had lasted more than 10 millennia and had been the most recent in seven cycles of glacial advance and retreat across the globe of the past 650,000 years.

Polar ice near Berlin, Hanover

Water froze, forming polar shield ice that also lay across Scandinavia, as far south as Berlin and Hanover. The freeze sucked the world's oceans lower by as much 125 meters (137 yards), leaving Britain — now pensive over Brexit — very much part of Europe's landmass.

Bands of hunter-gatherers, sometimes called the "Magdalenian,” mammoths, horses and woolly rhino had taken refuge in mostly tundra grasslands and scrub in an arc just north of Europe’s Alps from the Atlantic to the Black Sea, and especially in what is now France and the Iberian Peninsula, decorating caves such as the one at Lascaux.

From Bonn's clifftop: COP23 by night

Beyond their comprehension perhaps would have been the invisible, odorless and relatively small atmospheric constituent called carbon dioxide (CO2) and more climate-potent gases such as methane and nitrous oxide (laughing gas).

Earth warms, again

Cyclic warming was again in train, but this time humans, in what became known as the Holocene, began developing potent environment-changing technologies.

These would far exceed fire- and spear-making practiced during the decline of Neanderthals, who, however, left some Europeans with trace DNA in their genes, according to Max Planck researchers.

Cyclic changes in levels of atmospheric carbon dioxide — the "villain” at Bonn's UN climate talks — were still relatively routine, well below the rapid 20th-century surge to 407 parts per million now measured on Hawaii's Mauna Loa volcano by America's Scripps oceanographic observatory set up in 1958.

Ancient pollen, seeds and insects

How do we know all this? Not only because of ancient carbon dioxide contained in tiny air bubbles trapped in ice bored from Greenland and the Antarctic, but also from ancient pollen found in lake beds southwest of Bonn in Germany's volcanic Eifel region.

Extracting a frozen sediment core (Geo-science Institute, Uni Mainz)

The Eifel’s “maar” lakes, funnel-like volcanic vents, have over eons trapped sediments, layer by layer, revealing tree and plant pollen, insects, sand grains and dusty loess from drier ice phases.

Europe’s vegetation changes can be envisioned because the ancient pollen mix tells what trees existed or died off — birch, hazel, oaks, pines, juniper or grasses — each sensitive to certain conditions caused by factors such as temperature, moisture and acidity.

Knowing this, paleontologists have deduced the ancient vegetation cover, looking for clues also in ancient wood samples, such as growth rings.

The Eifel's last major volcanic eruption at Maria Laach 12,900 years ago carpeted campsites with ash, protecting bones, food remains and artifacts for present-day paleontologists to find and analyze.

Dauner Maar in the volcanic Eifel region

Climate-sensitive forest transformations

So, Bonn’s ancient residents, fast-forwarding, would have experienced Europe being transformed from frozen tundra into mixed, often dense forests dominated later by oak and then beech.

Entering the “Atlanticum” or climatic maximum, the Holocene's mild period from 8,000 to about 6,000 years ago, they would witnessed the adoption from the Middle East cultures of animal domestication and cereal cropping.

Dogger Bank mammoths

Ice sheets were melting; sea levels were rising, flooding, for example, the North Sea’s Dogger Bank, where fishing boats have since trawled up mammoth bones, and spear tips, possibly from drowned settlements.

Prehistoric Bonn: campsites, a Rhine with meanders, and looking south, the volcanic Eifel on the distant horizon.

West of the Urals, human individuals emerged who were no longer intolerant to milk but kept the ability to digest the protein lactose after childhood. It became feasible to keep cattle, goats, horses and sheep, drink their nutritious fluids and turn their wool into textiles.

Just as well, because of the relatively brief temperature slumps, one being the "Piora" oscillation about 5,800 years ago. Cereals grew only sporadically; swollen rivers inflicted erosion.

Early Middle Ages warmer

Fast-forwarding again: Civilizations in Egypt, Mesopotamia, China, the Americas and Italy came and went, leading up to Europe's warmer "high” Middle Age towards 1200 AD.

What some call the "Little Ice Age” set in from 1300 and lasted until 1850, a tumultuous era of famine, warfare and epidemics, with icy landscapes documented by painters such as Pieter Bruegel the Elder in 1565.

The cold helped put an end to the Emperor Napoleon’s march on Russia in 1812; the freezing weather was attributed to sunshine-blocking volcanic ash from Guadeloupe, which was followed by Indonesia's Tambora eruption in 1815.

Then came fossil fuels

As mass industrialization took over, the worldwide burning of fossil fuels, especially coal, sent "anthropological" carbon dioxide levels sky-high as compensatory "sinks" such as forests and oceans were overwhelmed.

Tempering this trend were volcanic ash showers, El Nino weather in the Pacific and shifting Gulf Stream flows in the Atlantic, and fluctuations in the Sun's radiation and Earth orbit wobble.

Rapid Hothouse

Created in 1988, the UN’s IPCC climate panel began warning that the Earth was being turned into a hothouse.

Its identified culprits were deforestation, but especially mass consumption of coal, oil and gas, releasing usable energy but also billions of tons of extra carbon dioxide.

It was a pattern already postulated in 1895 by Swedish scientist Svante Arrhenius.

What would the prehistoric couple have seen?

Gazing from their Rhine clifftop, probably terrified by the roar of fossil-fueled vehicles, trains, aircraft while watching river barges still shipping coal upriver to cities like Mannheim, our prehistoric couple and their dog would have been perplexed, even terrified.

On the horizon, beyond Bonn, they would see steam rising from two of Europe's larger coal-fired power stations, Niederaussem and Neurath.

Niederaussem's steam plume — but CO2 is invisible

Long used to the warmth of their campfire, they perhaps would have heard COP23 delegates calling for total “decarbonization” by 2050 and Pacific islanders pleading for severe reductions before 2020 to avert otherwise inevitable flooding of their island homes.

Conference progress

They would have heard climate activist Tracy Sony from Botswana saying progress had been made at the conference, but "finance" from wealthier countries was still needed so Africa could “leapfrog, especially in areas of agriculture and renewable energy.”

And, listening to climate sages such as German oceanographic researcher Professor Mojib Latif, our prehistoric couple would hear him say: "We are carrying out a large-scale experiment. We are basically gambling with our planet.”