Earth of 2100: Good for palm trees

[GrandMasterTerwynn]

Bad for polar bears!

Hot "Prehistoric" Conditions May Return by 2100, Study Says
Brian Handwerk
for National Geographic News
September 28, 2006

Earth's future could resemble its hottest ancient epoch, a new study says. Picture palm trees swaying in Canada, warm seas lapping at shorelines hundreds of feet higher than they are today—and no natural ice anywhere.

That was the scene some 50 million years ago, scientists say, and rising carbon dioxide levels could make Earth's future look much like this hothouse past.

The study shows that the high carbon dioxide (CO2) levels found during the Eocene epoch match the CO2 levels predicted for the end of this century by many global warming models.

The Eocene occurred between 56 million and 49 million years ago. It featured the highest prolonged global temperatures of the past 65 million years.

"Some frost-sensitive plants, like palm trees, lived to about 60 degrees north [for example, as far as southern Alaska] and south latitude," said geologist Tim Lowenstein of New York's Binghampton University. Lowenstein co-authored the new study, which appears in tomorrow's issue of the journal Science.

"[Palm tree remains] were found in the basin where our work was [completed] in Colorado and Wyoming," Lowenstein continued. "That would project Florida-like climates well up into Canada."

"There was no ice on any continent as far as we know," said Daniel Schrag, professor of Earth and planetary sciences at Harvard University in Cambridge, Massachusetts.

"There were forests in the Arctic and Antarctica," added Schrag, who is unaffiliated with the study. "There were crocodilians living on Ellesmere Island in the Arctic [map of Ellesmere Island region]."

The Eocene's oceans, according to fossil records of oxygen, were the warmest of the past 60 million years. They were also much higher than today's seas.

"Sea level was about 100 meters higher [328 feet]—mostly because there was no ice in Antarctica," Harvard's Schrag said.

"That's real global warming," Lowenstein added.

Rising CO2 to Spur a New Eocene?

Lowenstein and colleagues calculated ancient carbon dioxide levels by examining sodium carbonate minerals in Colorado, Wyoming, China, and Turkey.

They report that the Eocene's atmospheric carbon dioxide concentration was greater than 1,125 parts per million (ppm) by volume. Today's levels are only about 380 ppm, but that number is up from an estimated 280 parts per million before the industrial revolution.

Climate models vary widely, but those used by the United Nations' Intergovernmental Panel on Climate Change suggest that levels could range from 400 to 1,000 ppm by century's end.

The amount of fossil fuels humans use, and at what rate, are critical unknowns in any model of future CO2 levels.

"Depending on how much [fossil fuel] we burn, [Eocene carbon dioxide levels] would be very close to the upper range predicted for the next hundred years," Lowenstein said.

"We knew [the Eocene] was warm, and now we have evidence that the CO2 was high," he continued. "So this does prove a link between high CO2 levels and the warmest era on record."

"I think this is very interesting. Any new information that we can get on ancient CO2 levels is very important," Schrag said.

Risky Business

Modeling climate is a notoriously tricky business, and climatologists caution that many variables remain unknown.

"Back then there were no glaciers on the poles, the ocean currents may have been different, the world was a different world," Lowenstein said. "So as far as predictions, it's not fair to say that this is exactly what the climate will be like in a hundred years."

Harvard's Schrag agrees. But he suggests that the uncertainty inherent in current climate-modeling techniques could mean that current models underestimate future warming.

"CO2 alone is probably not enough to explain some aspects of the ancient climate," he said.

"There [were] palm trees in Wyoming, and palm trees don't grow where it gets cold in the winter. When you take a climate model designed for the modern climate and raise the CO2 levels this high, you don't get [Wyoming] winter temperatures warm enough for palm trees to survive.

"That tells us that there is something missing from the models," Schrag said.

Factors absent from current models—such as warming induced by cloud cover—may have amplified warming in the past.

"There's no reason we'd know about [cloud feedback under Eocene-like CO2 conditions] in the modern climate, because we haven't seen such high levels of CO2," he said.

"But it's important for thinking about future warming. It says that it's quite possible that current models are underestimating warming—and we may be in for some surprises in the future."

This clearly seems like a possible absolute worst-case scenario, given how they can't quite link the elevated CO2 levels in that time period with arctic climates warm enough to support palm trees. Still, that we might be capable of at least reproducing the levels of CO2 that were around when such a climate regime existed should be sobering.

[Cao Cao]

So a century from now, London may be a tropical paradise. Assuming any of it is left above water.
Yay! Something to look forward to.

[Guardsman Bass]

The Eocene was not only a helluva lot warmer (25 degrees Celsius average temperature in the mid-latitudes - pretty close to the Amazon Basin's current 27 degrees average temperature), but it also had a smaller temperature gradient (about half of what today's is).

It'd be one of those things that would be an absolute bitch for both life and human civilizations to adapt to, since essentially all the ecosystems that develop in environments colder than the Pacific Northwest would have to adapt or die, and most of the heavily populated areas in the world (the coastal cities) would be submerged.

Still, once it was over, it would open up a lot of new land for farming and inhabitance, so that's good for humans, I suppose; kind of making up for the land lost to the sea.

[GrandMasterTerwynn]

So a century from now, London may be a tropical paradise. Assuming any of it is left above water.
Yay! Something to look forward to. :)

Oh, that'd be the absolute best thing that could happen to London. The more likely thing to happen in a global warming scenario is the Greenland ice sheet goes into irrevocable melt-down and the resulting freshwater dump into the north Atlantic shuts down the Gulf Stream and the rest of Atlantic conveyor. The same conveyor that insures that Great Britain and much of Europe stays warm enough that polar bears don't take up residence for half the year.

For a while, at least, while the rest of the world gets warmer, much of Europe risks plunging into an ice age.

[Guardsman Bass]

On the bright side, all those new, warm, shallow seas covering the areas where the coast used to be would probably be a gold mine for sea life.

[momochan]

Sea life is going to have its hands full dealing with increased seawater acidification due to carbon dioxide.

We may not have to match prehistoric CO2 levels to get to prehistoric temperatures -- because we've also been releasing other greenhouse gases like nitrous oxide and some of the refrigerants. You have to look at CO2 equivalent.

[Surlethe]

Something else to look at is how quickly the globe warmed up to the Eocene temperature highs: it probably took thousands, hundreds of thousands, or even milions of years. It certainly didn't happen over the course of three hundred years. Life would have, I think, had plenty of time to adapt to the Eocene temperatures as the Earth warmed up; now, we're looking at reaching those temperatures over a century. If we go this route, it's likely that we'll be looking at many populations which will have been greatly reduced, if not driven to extinction.

Now that I think about it, wouldn't it also cause desertification in places which are now croplands?

[Sam Or I]

Can I homestead in Antartica now?

[Ariphaos]

Now that I think about it, wouldn't it also cause desertification in places which are now croplands?

No. Deserts are caused by a combination of factors.

1: Earth has a latitude-based water cycle. Warm water near the equator evaporates, and rains down over 15 degrees of latitude, and picks up more over the next 20 degrees of latitude to rain it down on the next 20, etc. Thus, most deserts are located between 15 and 35 degrees of latitude.

2: Cold ocean currents prevent the evaporation of water, causing desertification further east. There is a small, trapped, cold ocean current just west of the Sahara that some believe caused it to form.

3: Mountainous regions, or regions where winds have been carrying overland for an extended period of time can also cause desertification. For example, the Gobi desert.

Just one of the above factors is not enough. A hot Earth, in this scenario, will remove #2 worldwide, possibly even around Antartica, if it manages to disrupt the Antartic current.

Of course, this all takes over a thousand years.

Once a desert begins forming, several things occur
- The bleached sands reflect heat, meaning that the air above them gets hotter, preventing further rainfall.
- This also causes a runaway salinity breakdown, where the surrounding soil gets salted, killing the plants, trapping more salt, and then blowing it to nearby areas to kill more plants...

So it wouldn't necessarily be the end of deserts until they were somehow forced into recovery, however, most regions of the world would see a great deal more rain.

[Guardsman Bass]

Can I homestead in Antartica now?

You might want to wait a few decades until the bare bones of life could get re-established on the ground left behind.