Scientists drill deeper to uncover secrets of the Holocene

In a geological sense, the human race has barely existed for more than a fraction of Earth’s history.

If you were to compress all of Earth’s 4.6 billion year geological history into a 24-hour day, the rise of our ancestors wouldn’t occur until two minutes to midnight and Homo sapiens would barely emerge as the clock struck 12am.

There are a number of ways scientists can observe historical changes in the planet’s climate. Tree rings, layers of soil, or better still – ice cores. Human history is encompassed within an era that extends as far back as 11,700 years, across an epoch known as the Holocene, which roughly translates into the “entirely new” era in Greek.

How has the climate shifted over this lengthy era, and what could it suggest for where we’re heading?

Getting to the core of the problem

Ice cores are tremendously valuable records of Earth’s climate – particles of air are trapped beneath fallen snowflakes, and when enough of them fall en masse, these air particles are eventually turned into a series of bubbles which remain trapped in ice. These bubbles offer a snapshot of a moment in time, allowing scientists to see the composition of Earth’s atmosphere.

These slivers of ice can give us an accurate idea about roughly how our planet’s climate evolved, with some ice cores reaching 800,000 years into the past in places such as Antarctica, where the ice is at its thickest. We can tell how much CO2 or methane entered into our atmosphere and roughly when, based on how deep the bubbles are located.

As a result of this extensive archive of data, we are able to paint a picture of how human history has not only been shaped, but how it has ultimately shaped the climate in its own way. There was originally something of a ‘Holocene conundrum’ when it came to working out how history unfolded – reconstructions for sea surface temperatures seemed to suggest a noticeable warming period between 12,000 to 8,000 years ago, before a sudden cooling period up until the industrial revolution.

It implied that Earth’s climate was relatively choppy, and that human activity in the last 150 years simply warmed up the planet back up to levels last seen 8,000 years ago. However, as an article in the journal Nature reveals, more recent computer simulations for sea surface temperatures simply don’t match this assumption – scientists now theorise that original estimates of sea temperatures were significantly distorted to the upside by seasonal effects.

Crunching the right numbers

More up-to-date ways of analysing the data suggest that global temperatures were rising gradually from a lower base, before almost levelling out at the dawn of human civilisation. The new findings then suggest a highly anomalous spike in temperatures occurred at the same time of the industrial revolution was getting underway, suggesting that our impact on the planet was far more profound than once believed.

This idea of an anomalous spike chimes with data published by Our World in Data, which clearly shows how that atmospheric CO2 concentrations leapt to unprecedented levels at the same time as the human population recorded its fastest growth in recorded history.

These precious snapshots from ancient history point to an Earth which was colder for longer, and that despite our short time on Earth as a species, we have left a sizable mark on the planet – more CO2 than any point in recorded history and rapid rises in temperatures, which show little signs of abating. Whether we can flatten these curves and move them in the right direction depends on what we do in the here and now.

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