There is no solace in learning about carbon dioxide's new 66 million-year history.
A new, extensive analysis of the historical amounts of atmospheric carbon dioxide and the temperatures that accompanied it paints a frightening picture of the possible future of Earth's climate. The research examines geologic records that extend back 66 million years, providing a historical context for current concentrations.
One important finding is that, contrary to what some previous estimates suggest, the last time atmospheric carbon dioxide levels regularly approached the levels caused by humans was fourteen million years ago. It states that greenhouse gas emissions have a profound impact on the long-term climate, with repercussions that might last for millennia.
Over seven years, 80 academics from 16 nations worked together to compile the report. The magazine Science publishes it.
"All of us have known for decades that adding CO2 to our atmosphere raises the temperature," said Bärbel Hönisch, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory and director of the research effort. "This research gives us a much more robust idea of how sensitive the climate is over lengthy ."
Global average temperatures will rise 1.5 to 4.5° Celsius (2.7 to 8.1° Fahrenheit) for every doubling of atmospheric CO2, according to mainstream projections, over periods ranging from decades to centuries. The present consensus places planetary sensitivity at between 3.6 and 6°C of warming per doubling, however at least one popular research from recently contends that this is an underestimate.
Regardless, many scientists believe that we must do everything in our power to prevent the globe from rising more than 2 degrees Celsius this century, and all projections show that this is within striking distance given the present trajectory.
The atmospheric concentration of carbon dioxide was around 280 ppm in the late 1700s. Our current concentration is 420 ppm, up around 50%; by the century's end, it may rise to 600 ppm or more. Consequently, we have already risen around 1.2°C (2.2°F) since the late 19th century, putting us somewhere along the uncertain warming curve.
Most projections of future warming are based on analyses of historical temperature-CO2 level correlations, regardless of the precise nature of those relationships. To do this, they examine things like the chemical composition of old soils and sea sediments, the structure of fossilised plant leaves, and air bubbles included in ice cores.
Instead of gathering fresh data, the members of the consortium pooled their existing expertise to evaluate the validity of previously published research. They adjusted some to reflect the most recent analytical methods and removed others that they deemed out of date or lacking in light of fresh evidence. After reviewing the available data, they arrived at a new 66-million-year CO₂ against temperature curve and reached an agreement on what they term "earth system sensitivity." They claim that this metric predicts a staggering 5 to 8°C increase in global warming due to a doubling of CO2.
Importantly, Earth system sensitivity does not account for human-relevant decades or centuries but rather changes in the climate over hundreds of thousands of years. Interconnected Earth processes, the scientists argue, may cause temperature rises over the long term, even if CO2 in the air has no direct impact. Among them, we may find alterations to the Earth's plant cover, changes in cloud and aerosol composition, and the melting of the polar ice sheets, the latter of which would decrease the planet's capacity to reflect solar energy.
We can't use this to give you an accurate prediction of the weather in the year 2100. “But it does have a bearing on present climate policy,” said Dana Royer, a paleoclimatologist from Wesleyan University and one of the authors. It backs up our prior assumptions. Additionally, it informs us that the impacts would be gradual and cascading, lasting for a very long time—thousands of years.
In order to untangle processes that operate on short versus long time periods, climate modellers will be able to include the more robust data into their research, according to Hönisch. This will help them make more accurate predictions about the future. The data used in the initiative would be updated regularly and made accessible in an open database, she said.
The new research strengthens our knowledge of some historical periods and refines measurements of others; nonetheless, it does not dramatically modify the previously known link between CO2 and temperature. The study covers the so-called Cenozoic era.
Since the Earth was mostly devoid of ice between around 66 and 56 million years ago, and since some research has shown that CO2 concentrations were relatively low at this time, the most remote interval has remained a mystery. This raises some questions about the validity of the CO₂–temperature link. After removing the least credible projections, the group found that CO2 levels were very high, with levels of 600 to 700 parts per million, which is on par with what may be achieved by the century's end.
Long thought to have occurred about 50 million years ago, when CO2 levels reached 1,600 ppm and temperatures were 12 °C greater than today, the researchers' findings corroborate this long-held notion. However, the present-day Antarctic ice sheet started to form when CO2 levels decreased enough, which was around 34 million years ago.
A further long-term decrease in CO2 occurred after this, with fluctuations, and it was at this time that many current plant and animal species emerged. According to the authors of the article, this indicates that changes in CO2 levels impact ecosystems as well as climate.
The most recent study indicates that levels of carbon dioxide (CO2) were regularly lower than today's 420 ppm about 14 million years ago, after having been persistently higher than today at around 480 ppm around sixteen million years ago. Around two and a half million years ago, CO2 levels hit around 270 or 280 elements per million, setting off a succession of cold ages, while the drop persisted. About 400,000 years ago, modern people emerged at or below there, and we stayed put until approximately two centuries prior when we began to significantly alter the atmosphere.
According to Gabriel Bowen, a professor at the University of Utah and one of the study's co-authors, "across a range of conditions never seen by our species," the earth has already entered a new temperature regime. "It's ought to make us stop and question what the right path ahead is."
A bigger project has grown out of the collaboration, and its new mission is to trace the history of carbon dioxide (CO2) and climate change across the whole Phanerozoic aeon, which began 540 million years ago and continues to the current day.
