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We entered a deeply unknown planetary territory.
In a context where American politicians are still wondering whether climate change is man-made (that's the case), it is highly likely that we have actually increased carbon dioxide in the Earth – a powerful greenhouse gas – at the highest level they've known for 15 million years.
This figure of 15 million is much higher than a statistic frequently cited by geologists and climatologists: current carbon levels are the highest ever recorded on Earth for at least 800 000 years – because irrefutable evidence is trapped in the old ice of the planet.
Although scientists point out that air bubbles preserved in ice are the gold standard for carbon, there are less direct, but still quite reliable, ways to measure carbon dioxide levels on carbon. the Earth a long time ago. These measurements, roughly called proxies, include the chemical composition of long dead plankton and the evidence stored in the respiratory cells, or stomata, of ancient plants.
Scientists have identified this figure of 15 million by measuring and re-measuring proxies around the world.
Old air stored in ice bubbles.
Image: nasa
"It's good science, but it's an indirect measure," said Michael Prather, professor of terrestrial systems science at the University of California, Irvine, in an interview.
"And there are several sources of data," added Prather, lead author of the UN's climate reports, citing evidence of carbon dioxide in fossilized marine life. "It's not just the crazy number of a person."
Direct Air Show Measurements Recently, carbon dioxide levels reached 410 ppm, the highest number ever recorded.
"Most of the time, carbon dioxide was less than 400 ppm for about 14 million years," said Matthew Lachniet, a paleoclimatologist at the University of Nevada in Las Vegas.
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There may have been a time, about 3 million years ago, during an extremely hot period called the Pliocene epoch – when the sea level was 16 to 131 feet higher than today – during which carbon concentrations could have moved closer to current levels.
"However, the concentration of CO2 currently in the Earth's atmosphere is higher or nearly as high as it has been in the last 15 million years," said Daniel Breecker , paleoclimatologist at the Austin Jackson School of Geosciences at the University of Texas. , said by e-mail.
<p class = "canvas-atom canvas-text Mb (1.0em) Mb (0) – sm Mt (0.8em) – sm" type = "text" content = "The critical difference today is however that the carbon emissions should continue to increase. unprecedented burning fossil fuels, carbon accumulations will simply continue to increase. "Data-reactid =" 42 "> The critical difference today, however, is that carbon emissions should continue to rise. unprecedented burning fossil fuels, carbon accumulations will simply continue to increase.
Different indicators, such as phytoplankton (red), offer scientists a good range (blue background) of past estimates of atmospheric carbon dioxide.
Image: United Nations / Ipcc
"Of course, C02 concentrations do not stop today," said Lachniet. "We will probably exceed 550 to 600 ppm."
Lachniet noted that these types of high carbon concentrations have not been seen on Earth for more than 20 million years.
"It makes this conversation even harder," he said.
However, some members of the climate community have even argued that the current climate contains the highest concentration of greenhouse gases – when gases such as methane (natural gas) and nitrous oxide are added to the mixture – 20 million years.
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In the end, it's not just the actual concentration of carbon dioxide that counts, it's the planet's sensitivity to this dramatic carbon buildup, Breecker noted.
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Since the beginning of the Industrial Revolution, the Earth's average temperature has risen by 1.8 degrees Fahrenheit, or 1 degree Celsius.
Major consequences have already been observed regularly in the Earth's water cycle – increasing the probabilities of extreme extremes in floods and drought. The most predictable results, record heat waves and historic forest fires, are manifesting themselves on a global scale, as well as more complex atmospheric changes.
"He [global warming] The rising sea level and worsening storm surges make the atmosphere more humid, resulting in floods caused by extreme rainfall and warming ocean temperatures provides additional energy to the storms. Tropical storms, "Stefan Rahmstorf, climate scientist, head of the Earth System Analysis at the Potsdam Impact Institute Climate Institute, said in September.
"The polar ice is melting, in the ocean the Gulf Stream system is weakening and in the atmosphere, the jet stream becomes strange," added Rahmstorf.
Unlike previous geological epochs, the defining circumstance today is not just high carbon emissions in the air – it is the speed with which it accumulates.
The natural world charges and removes carbon from the atmosphere over long periods ranging from several thousands to tens of thousands of years.
For example, a warm period called Eemian, which ended about 120,000 years ago, has slowly melted a significant portion of the Greenland ice sheets – even with very low carbon concentrations of about 280 ppm.
But these days, the climate has not been caught yet.
"We are warming up so fast that we have not even begun to let Greenland melt," noted UC Irvine's Prather.
Where civilization eventually becomes dominant, in terms of carbon emissions, global society depends on the speed with which it moves to clean energy and produces electricity without relying heavily on fossil fuels.
"I would say that what is really important is where we are stabilizing," said Lachniet. "Over the next hundred years, we have truly defined the next 10,000 years of climate history."
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