Ann Arbor (Informed Comment) – – The National Oceanic and Atmospheric Administration reports that for the 11th consecutive year, human-caused emissions of carbon dioxide and other greenhouse gases increased at the same rate as has been common for the past decade. In other words, nothing the world has so far done has caused the rate of growth in the production of carbon dioxide to decline. NOAA says that “The global surface average for CO2 rose by 2.13 parts per million (ppm) to 417.06 ppm.”
Before the industrial revolution, there were typically an average of 280 parts per million of carbon dioxide in earth’s atmosphere. That level of CO2 kept the world a little cool, and it is those conditions under which humanity evolved and functioned. Certainly, for all the time there has been civilization, we lived in a 280 ppm carbon world.
The last time there were about 400 ppm of CO2 in the atmosphere was the Pliocene era, roughly from 5 to 2 million years before the present. In the middle of that era, about 3 million years ago, temperatures were particularly high. Temperature fluctuated in the past because the earth went through periods of high volcanic activity. Over millions of years, the eruptions could gradually increase the CO2 in the atmosphere. Then over millions of years, oceans, igneous rock and other carbon sinks would absorb it again. If the volcanoes settled down for a while, the CO2 levels fell. Again, this took hundreds of thousands or millions of years.
Humans are much more virulent than a few volcanoes. We have done to the earth’s atmosphere in 270 years what it used to take nature millions of years to do.
And apparently we are not done. We continue to blast carbon dioxide into the atmosphere. Last year our global emissions were up nearly 1%, to 36.8 billion metric tons. We aren’t even stabilizing our massive annual carbon pollution, much less reducing it. I look out at traffic jams full of CO2-spewing internal combustion engine vehicles, or at office buildings and housing developments heated by coal and gas, and I think to myself “Are you crazy?”
There is a simple little trick that could save us from the worst effects of this CO2 build-up. Most of the carbon dioxide we have put into the atmosphere will be absorbed by the oceans over the next 150 years, getting us back down to 350 ppm. But there is a catch. The oceans’ absorptive capacity is not infinite. If we go on putting billions of tons of CO2 into our environment past about 2050, we will outrun the oceans’ ability to take it in. That outcome would doom us to the Middle Pliocene or worse.
As a historian, I am glad to see climate scientists reaching back to previous epochs to get a sense of what our earth will be like when the full impact of the climate emergency begins hitting. As a human, I am terrified at the conclusions you reach by making that analogy.
I have pointed out that in the Middle Pliostene,
“Temperatures in the middle Pliocene were on average 2-3 degrees C. (3.6 – 5.8 degrees F.) higher than today. The Arctic was 10 degrees C. hotter than today’s. Seas were roughly 90 feet higher. Some places now wet were desert-like. See this link for what would happen to five cities under this scenario.
This 90 feet sea level rise is therefore almost certainly baked in and will occur, over the next few hundred years (oceans are huge and cold and take time to warm up). I wouldn’t buy real estate in Miami or lower Manhattan with an idea of passing it on to your grandchildren. Any beachfront property is ephemeral.
The cycles of drought and monsoon flooding were extreme in the west of North America during the Middle Pliocene, and we are already seeing some evidence of this deadly one-two punch in California in the twenty-first century.
On another occasion I observed,
During the Pliocene Climatic Optimum, there does not appear to have been much surface ice in the northern hemisphere, and the North Pole was heavily forested. Only Antarctica had ice sheets. Because most of the ice had melted, sea levels were between 15 and 75 feet higher than today, depending on which part of the 400,000-year period you look at. It was so warm that giant camels and rhinoceri roamed Indiana, as proved by the remains in a sinkhole that escaped being scoured away by later glaciers.
NOAA’s sea rise calculator tool only let me raise the oceans ten feet, but you can see that even at that level, less than what 421 ppm of atmospheric CO2 will produce in the coming centuries, the southern half of Florida and most of its coastal regions are just gone. Miami is gone. Savannah and New Orleans are also gone. This sort of sea level rise, and indeed much more, is already baked into our future. It will happen if we don’t abruptly stop flooding the atmosphere with CO2. If we do stop, the seas will absorb a lot, but their capacity is not infinite.
During Climate Optimums of eras such as the Miocene and Pliocene, Albert C. Hine et al. write,
“During the Eocene Climatic Optimum, the Florida Platform was mostly covered by warm tropical/subtropical seas during an extended sea level highstand (Fig 15.7B). Carbonate sedimentation dominated in these shallow seas. The accumulating fossiliferous sediments formed the upper limestone portion of Florida’s carbonate platform and generated the rocks seen today in mines, pits, sinkholes, and sometimes at the land surface. These sediments and rocks formed the Ocala Limestone (Fig. 15.7A). The Miocene Climatic Optimum was also a period of relatively high sea level, during which Florida’s abundant phosphate deposits accumulated.”
During the warm eras of the Pliocene there was much less desert in, e.g., Africa. The Sahel region stretching from Senegal to Sudan, which is today arid and threatened with desertification, was lush tropical forest, possibly all the way across.
Here is what the North American Southeast looks like at 70 feet sea level rise, which is where we are likely going over time:
h/t Vivid Maps .
All the Republican climate deniers in Congress will have to find somewhere else to meet in a few centuries, since the Capitol will be under water.
Sea level rise and tropical weather everywhere, however, are not the only dangers humanity now faces. Extreme weather, frequent and large hurricanes, sudden floods and wildfires, will be signs that the climate system has become increasingly chaotic. Civilization depends on planning, on a knowledge of what the future will bring. As we make our climate chaotic, we will lose that assurance, and the uncertainty will be among our greatest challenges.
At this rate, we will be up to 440 ppm by 2030, and up to 500 ppm by 2050. And that is if the rate of new emissions doesn’t increase. That would put us back in the Eocene, just after the extinction of the dinosaurs.
You wouldn’t like the Eocene.
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