New evidence suggests that the planet could well be in the grips of another Ice Age by now if it weren't for the actions of farmers thousands of years ago.
A study published in the journal Scientific Reports says that early agricultural practices significantly increased emissions of the heat-trapping gases carbon dioxide and methane.
Had it not been for those practices, Earth's climate would be significantly cooler today, the research from the University of Wisconsin-Madison shows.
When compared to a similar geologic time period 800,000 years ago, the global average temperature was 1.3degC cooler than in 1850.
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While studying carbon dioxide and methane trapped in Antarctic ice, researchers noticed that methane emissions began decreasing about 10,000 years ago, but started to increase again about 5000 years later.
A similar phenomenon was observed with carbon dioxide concentrations, which began falling abound 10,000BC years ago but rose again 3000 years later.
"The only explanation I could come up with is early agriculture, which put greenhouse gases into the atmosphere and that was the start of it all," says study co-author William Ruddiman.
By clearing land to plant crops, flooding fields to grow rice and raising livestock, farmers around the globe warmed up the climate between about 7000BC and 5000BC.
Different agricultural practices across different continents are all thought to have contributed to the increase in carbon dioxide and methane, from the widespread deforestation in Europe about 6000 years ago to the spread of methane-producing rice paddies throughout northeast Asia about 5000 years ago.
Agriculture threw a spanner in the works of Earth's natural climate cycles, in which slight fluctuations in our orbit or changes in the way we tilt on our axis can throw the planet into Ice Ages lasting thousands of years.
Astronomers can predict these warming and cooling cycles with precision, but the farming practices of humans several millennia ago made such a difference to the climate that we're now in uncharted territory.
Lead study author Stephen Vavrus says people shouldn't get the wrong idea about the research and think that early farmers saved us from an Ice Age.
"Things are so far out of whack now, the last 2000 years have been so outside the natural bounds, we are so far beyond what is natural."
Professor Ruddiman says that by meddling with Earth's natural climate balance, humans may have sentenced ourselves to a future that's just as unliveable as an Ice Age but far less predictable.
"The phenomenal fact is, we have maybe stopped the major cycle of Earth's climate and we are stuck in a warmer and warmer and warmer interglacial."
Newshub.
