Human influence over the planet's climate could have disastrous effects by the end of the century, documents the latest study by Southampton University.

If current rates of burning fossil fuel are maintained over the next 100 to 200 years, carbon dioxide concentrations in the Earth's atmosphere could more than double, reaching the highest level since the Triassic, the research reports.

That means an increase from 400 parts per million — the present CO2 concentration — to values exceeding 900 ppm at the beginning of the 23rd century. Failure to reduce greenhouse gas emissions could also result in a state of global warming last encountered 420 million years ago.

According to other estimates, in the event all fossil fuels on the planet are depleted, atmospheric CO2 concentrations could reach 5,000 ppm by the year 2400.

Greenhouse Effect Revealed By Plant Fossils

In their investigation, researchers led by Gavin Foster, an isotope geochemistry professor at Southampton, reviewed 112 published papers compiling over 1,200 estimates of ancient CO2 concentrations.

Their study, featured in the journal Nature Communications, comprised a continuous data record tracing back CO2 concentrations in the past half a billion years. These data showed that, if humanity uses up all available fossil fuels, atmospheric concentrations could boost to levels unprecedented since the beginning of the record.

Due to the impossibility of directly measuring CO2 concentrations from millions of years ago, Foster's team turned to "indirect proxies" for evidence of gas fluctuations in the atmosphere.

Instead, they examined information on plant fossils, carbon isotopic composition in ancient oceans and soil samples, as well as boron isotopes in fossilized shells.

Their analysis uncovered that, although CO2 concentrations normally oscillated throughout the entire studied interval — shifting naturally from nearly 200-400 ppm in the Earth's colder periods to almost 3,000 ppm in warm 'greenhouse' cycles — the global warming speed our planet is currently experiencing is higher than expected.

This suggests that anthropogenic emissions caused by human activities have a much greater impact than previously considered, since it escalated CO2 concentrations by nearly 50 percent in the past 150 years. Before the rise of industrialization, atmospheric concentrations were leveled at 280 ppm, whereas a 2016 measurement revealed they soared to 405 ppm.

The Sun's Contribution To Climate Change

Global warming is determined not only by the greenhouse effect, but also through the combined results of CO2 emissions and solar activity. Because of internal nuclear reactions, the sun gradually increases in power, becoming more radiant over time.

As a result, it shines exponentially brighter now than it did 420 million years ago. Although CO2 levels of that time were comparatively higher, the overall warming effect of greenhouse gases and sunlight was lower, "because the Sun was dimmer back then," researchers explain in a Southampton new release.

Until now, scientists didn't fully understand why, "despite the Sun's output having increased slowly over time, scant evidence exists for any similar long-term warming of the climate," says Dana Royer, study co-author and professor at Wesleyan University.

The study indicates Earth's climate was on a stable course for millions of years because the greenhouse effect was counterbalanced by the lower solar intensity.

Now, gas emissions have reached an atmospheric CO2 record, whose impact is accelerated by the growing power of the sun. The rapid climate change, which presently surpasses the geological norm, will be even more affected if we use up all our fossil fuel.

In such a case, current-rate anthropogenic emissions could lead to CO2 concentrations of 2,000 ppm by the year 2250, study authors conclude.

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