The last time carbon dioxide in the atmosphere consistently matched today’s human-driven levels was 14 million years ago, according to a large new study published in the journal Science. This study, conducted by a consortium of 80 researchers across 16 countries, provides a grim picture of where Earth’s climate is headed.
Lead author Baerbel Hoenisch of the Columbia Climate School’s Lamont-Doherty Earth Observatory emphasizes the significance of these findings, stating, “It really brings it home to us that what we are doing is very, very unusual in Earth’s history.”
The research covers a period from 66 million years ago until the present, utilizing biological and geochemical signatures from the deep past to reconstruct the historic CO2 record with greater precision than ever before. The analysis reveals that the last time the air contained 420 parts per million (ppm) of carbon dioxide was between 14 and 16 million years ago, a far more distant timeframe than previously indicated by prior analyses of 3 to 5 million years.
Before the late 1700s, atmospheric carbon dioxide levels were around 280 ppm. This means that humans have already caused an increase of about 50 percent of the greenhouse gas, which has resulted in a 1.2 degrees Celsius warming of the planet compared to pre-industrialization levels.
The significance of these findings becomes even more apparent when considering the timeline of human evolution. Hoenisch explains, “What’s important is that Homo, our species, has only evolved 3 million years ago. And so our civilization is tuned to sea level as it is today, to having warm tropics and cool poles and temperate regions that have a lot of rainfall.”
If global CO2 emissions continue to rise, projections indicate that we could reach between 600 and 800 ppm by the year 2100. These levels were last seen during the Eocene, 30 to 40 million years ago, when Antarctica was not covered in ice and the world’s flora and fauna looked vastly different.
To gather data for this study, researchers utilized proxies, such as the chemical composition of ancient leaves, minerals, and plankton, to indirectly derive atmospheric carbon at different points in time. This allowed them to look further back into the past than ice cores, which generally provide information for hundreds of thousands of years.
The study confirms that the hottest period over the past 66 million years occurred 50 million years ago when CO2 levels spiked to as much as 1,600 ppm, resulting in temperatures that were 12 degrees Celsius hotter. This was followed by a long decline.
By 2.5 million years ago, carbon dioxide levels were around 270-280 ppm, marking the beginning of a series of ice ages. These levels remained relatively stable until modern humans arrived 400,000 years ago and began burning fossil fuels on a large scale.
According to the research team, a doubling of CO2 is predicted to warm the planet by 5 to 8 degrees Celsius. However, this warming would occur over a long period, with rippling effects through Earth systems. For example, melting polar ice caps would reduce the planet’s ability to reflect solar radiation, creating a reinforcing feedback loop.
While the implications of this study are concerning, it is essential to emphasize its relevance to policymakers. Understanding the Earth’s carbon record and its historical context can guide decisions that aim to mitigate the effects of climate change and protect the planet for future generations.
This groundbreaking research, representing the updated consensus of the scientific community, serves as a stark reminder of the urgent need for global action to address rising carbon dioxide levels and their impact on Earth’s climate.
Source: The Manila Times
