A new 66-million-year history of carbon dioxide provides some comfort for today

A new assessment of ancient atmospheric carbon-dioxide levels and temperatures paints a grim picture of where global climate may be headed. The study includes geological data in the past 66 million years, and presents today’s information in detail and time depth.

Among other things, it shows that the last time atmospheric carbon dioxide levels reached today’s human levels was 14 million years ago—much longer. ago. some reviews are available up to date. It shows that the climate is very sensitive to greenhouse gas emissions, and the stressful effects may develop over thousands of years.

The study was gathered over seven years by a consortium of more than 80 researchers from 16 countries. E appeared in the journal Science.

“We’ve known for a long time that the addition of CO₂ in our atmosphere to increase the temperature, “says Bärbel Hönisch, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory, who coordinated the consortium. “This study gives us an idea more robust to climate sensitivity on longer time scales.”

Conventional estimates show that on the scale of decades to centuries, all the doubling of CO is in the atmosphere.₂ global temperatures will increase 1.5 to 4.5° Celsius (2.7 to 8.1° Fahrenheit) higher. However, at least one recent widely read study argues that the current consensus underestimates the sensitivity of the planet, putting it at 3.6 to 6°C of the warm to double.

In any case, according to current trends, all calculations put the planet at risk of close to or more than 2 ° warming this century, and most scientists agree that we should avoid it if possible.

In the late 1700s, the atmosphere contained about 280 parts per million (ppm) of CO.₂. We have now reached 420 ppm, an increase of about 50%; by the end of the century, we may reach 600 ppm or more. As a result, we are now in a temperature uncertainty, with an increase of about 1.2°C (2.2°F) since the late 19th century.

Regardless of how hot it turns out to be later, most estimates of future warming come from research and how to track it. the temperature in CO₂ situation in the past. For this, scientists study things including the air trapped in ice, the chemistry of ancient soils and sea sediments, and the structure of plant leaves.

Consortium members did not collect new data; rather, they came together to categorize published studies to assess their reliability, based on empirical knowledge. They excluded some they found outdated or inadequate in understanding new research, and reclassified others to account for the latest research methods. They then calculated the new 66-million-year CO₂ compared to temperature based on all the evidence so far, come to a consensus on what they call “Earth system sensitivity.” At this rate, they say, the doubling of CO₂ it is predicted to warm the planet by 5 to 8°C.

The big reveal: The sensitivity of the Earth to explain climate change over hundreds of thousands of years, not the decades and centuries that humans are concerned about. The authors say that, in the long term, the increase in temperature that can emerge from the global warming process goes beyond the immediate use of the greenhouse made by CO.₂ in the air. These include the melting of the polar ice sheets, which reduces the Earth’s ability to reflect the sun’s energy; changes in ground cover; and changes in clouds and atmospheric aerosols can increase or decrease temperatures.

“If you want us to tell you where the temperature will be in the year 2100, we’re not going to tell you that. But it has an impact on climate policy over time. now,” said author Dana Royer, a paleoclimatologist at Wesleyan University. “It reinforces what we already think we know. It also tells us that there are slow, gradual effects that will last for thousands of years.”

Hönisch said that the study will be useful for climate modelers who are trying to predict what will happen in the next several years, because they will be able to feed new information into their research, and eliminate processes that operate on short and long term scales. He said that all the project’s data is available in an open database, and will be updated on a regular basis.

The new study, covering the period known as the Cenozoic, does not renew the traditional relationship between CO.₂ and heat, but it strengthens the light at times, and clears the fruit at others.

The most distant period, from about 66 million to 56 million years ago, is something of a disaster, because the world was very much ice, but some studies suggested CO.₂ productivity was relatively low. This caused a doubt between the CO₂ and heat. However once the consortium dismissed the estimates they considered the most reliable, they concluded that CO₂ it was very high—about 600 to 700 parts per million, compared to what could be achieved by the end of this century.

The researchers confirmed the long-held belief that the hottest period occurred about 50 million years ago, when CO₂ it peaked at 1,600 ppm, and temperatures were up to 12°C higher than today. But about 34 million years ago, CO₂ it fell enough that the Antarctic ice began to form today.

With some ups and downs, another long CO followed₂ skin, where the ancestors of many of today’s plants and animals grew. This suggests, say the authors of the paper, that changes in CO₂ it affects not only the weather, but the environment.

The new analysis suggests that about 16 million years ago was the last CO period₂ was still higher than now, about 480 ppm; and by 14 million years ago it had sunk to today’s level of 420 ppm. The decline continued, and about 2.5 million years ago, CO₂ reached about 270 or 280 ppm, starting a series of ice ages. It is below the time that modern humans arrived about 400,000 years ago, and continued there until we began to interact with the environment on a large scale about 250 years ago.

“Regardless of the degree of temperature change, it is clear that we have already brought the planet to many levels that our species has not seen before,” said researcher Gabriel Bowen, a professor at the University of Utah. “We have to stop and ask what is the right way forward.”

The consortium has now changed to a big job it is intended to chart how CO₂ and the weather occurred over the entire Phanerozoic eon, from 540 million years ago to the present.