Carbon dioxide levels heading towards values not seen in 200m years, the sun gradually getting stronger over time

BE2C2 Report — Carbon dioxide concentrations are heading towards values not seen in the past 200 million years. The sun has also been gradually getting stronger over time. Put together, these facts mean the climate may be heading towards warmth not seen in the past half a billion years.

Some will point out that Earth’s climate has undergone similar changes before. So what’s the big deal this time?

Yes, the climate has changed in the past, but the current speed of change is highly unusual. For instance, carbon dioxide hasn’t been added to the atmosphere as rapidly as today for at least the past 66m years.

In fact, if we continue on our current path and exploit all convention fossil fuels, then as well as the rate of CO₂ emissions, the absolute climate warming is also likely to be unprecedented in at least the past 420m years. That’s according to a new study published in Nature Communications.

Just prior to the industrial revolution, for every million molecules in the atmosphere, about 280 of them were CO₂ molecules (280 parts per million, or ppm). Today, due primarily to the burning of fossil fuels, concentrations are about 400 ppm. In the absence of any efforts to curtail our emissions, burning of conventional fossil fuels will cause CO₂ concentrations to be around 2,000ppm by the year 2250.

This is of course a lot of CO₂. A new compilation of data shows that around 200m years ago, when dinosaurs first evolved, Earth had a greenhouse climate state with atmospheric CO₂ around 2,000-3,000ppm.

Life in the planet’s last greenhouse period, the Eocene (Jay Matternes / Smithsonian Museum, CC BY)

High concentrations of carbon dioxide don’t necessarily make the world totally uninhabitable: the dinosaurs thrived, after all. Will mankind be able to thrive too?

There is no doubt that humanity will face major socio-economic challenges dealing with the dramatic and rapid climate change that will result from the rapid rise to 2,000 or more ppm.

The new study also shows that the same carbon concentrations will cause more warming in future than in previous periods of high carbon dioxide. This is because the Earth’s temperature does not just depend on the level of CO₂ (or other greenhouse gases) in the atmosphere. All our energy ultimately comes from the sun, and due to the way the sun generates energy through nuclear fusion of hydrogen into helium, its brightness has increased over time. Four and a half billion years ago when the Earth was young the sun was around 30 per cent less bright.

What really matters is the combined effect of the sun’s changing strength and the varying greenhouse effect, the study said.

Looking through geological history the study generally found that as the sun became stronger through time, atmospheric CO₂ gradually decreased. On average, both changes cancelled each other out. Not this time though!

The study did not find any past time period when the drivers of climate, or climate forcing, was as high as it will be in the future if we burn all the readily available fossil fuel. Nothing like it has been recorded in the rock record for at least 420m years.

A central pillar of geological science is the uniformitarian principle: that “the present is the key to the past”. “If we carry on burning fossil fuels as we are at present, by 2250 this old adage is sadly no longer likely to be true,” wrote Gavin Foster a professor of isotope geochemistry at the University of Southampton, Dana Royer a professor of earth and environmental sciences at Wesleyan University and Dan Lunt a professor of climate science at the University of Bristol in The Conversation (theconversation.com) in their joint article.

“It is doubtful that this high-CO₂ future will have a counterpart, even in the vastness of the geological record,” the authors said.

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