Gwynne Dyer is a Canadian-born independent journalist whose column is published in more than 175 papers in 45 countries.

by Gwynne Dyer

Five hundred years ago the native people of the Americas were hit by half a dozen plagues as bad as the Black Death, one after another, and 95% of them died. The plagues of the ‘Great Dying’ don’t sound that bad – measles, influenza, diphtheria, smallpox – but for the native people they were deadly.

When the tens of millions of native Americans died,  the forests grew back on the land they used to farm. All those forests absorbed so much carbon dioxide that the average global temperature dropped, and what would otherwise have been a minor cyclical cooling became the Little Ice Age. It got so cold that there were famines in Europe. Climate justice, maybe?

The lead researcher of the team at University College London who joined up the dots is doctoral candidate Alexander Koch. (He hasn’t even got his PhD yet.)  It’s quite a story.

When Christopher Columbus arrived in the Caribbean in 1492, there were about 60 million people living in the Americas, and 99% of them were already farmers. Eurasian civilisations had a bit of a head-start on them technologically, but their numbers and their economies were very similar: there were 70 or 80 million Europeans, and most of them were farmers too.

A century later there were only 6 million native Americans left: a 90% fatality rate. Yet at that time, there were still only about a quarter-million Europeans in the Americas. It wasn’t the Europeans who did the killing – it was their diseases.

The native Americans had no resistance to the quick-killer Eurasian diseases that the Europeans brought with them. Those diseases had emerged in the densely populated countries of Europe and East Asia one at a time over thousands of years, passing from the herds and flocks of  domesticated animals to their human owners, who now also lived in herd-like conditions.

Each one of these new diseases killed millions before the survivors developed some resistance, but the Asian, European and African populations had time to recover before the next one emerged. The native Americans got all the plagues at once, and they died like flies.

This caused the largest abandonment of farmland in all history, which is what really interests Alexander Koch and his colleagues. As the forests grew back, they absorbed huge amounts of carbon dioxide, cutting the amount in the air by about ten parts per million (10 ppm).

The reforestation dropped the average global temperature enough to caused the Little Ice Age, which lasted for more than two hundred years and killed another couple of million people in local famines in Eurasia.

Our impact on the environment has now grown so large that a ten ppm cut in atmospheric carbon dioxide is almost meaningless. We are currently adding around ten ppm of carbon dioxide to the air every four years – but if we were to reforest all the land that was cleared around the world in the past 150 years but is not prime agricultural land, we could sequester 50 ppm of carbon dioxide.

That might win us the time we need to get our carbon emissions down without triggering runaway warming. Instead, the Brazilians elect Jair Bolsonaro to clear-cut the Amazon, and the United States elects Donald Trump to outsource US climate policy to the fossil fuel industry.

We are better informed than the native Americans about the factors that will decide our fate, but we may be no better than they were at avoiding it.