TURNING THE CLIMATE CLOCK BACK 3.3 MILLION YEARS

"BY 2025, CO2 LEVELS WILL BE HIGHER THAN THEY'VE BEEN FOR THE LAST 3.3 MILLION YEARS" [Nature Scientific Reports July 10, 2020]

Let's see. What was going on 3.3 million years ago?

--Humans like us were just a gleam in evolution's eye. The most promising potential ancestor around then was Australopithecus, an apelike creature living in southern Africa who may have been the first to use shaped stones to smash open bones for their marrow. 

--Earth wouldn't enter the current geologic epoch, the Holocene, for another 3,288,000 years. It was then in the middle Pliocene. 

--North and South America hadn't yet collided and connected. 

--North America sported two elephant-like species, hyenas, small, three-toed ancestors of modern horses, bone-crushing dogs, giant bears and three species of huge, saber-toothed cats. 

Smilodon populator--one of North America's

Pliocene saber-toothed cats

Credit: Charles Knight/American Museum of Natural History

--Humans wouldn't set foot on the continent for another 3.27 million years.

--Crucially, from our point of view, atmospheric CO2 levels were comparable to today's (somewhere between 381 and 427 parts per million), yet global temperatures were 2 to 3 degrees C (3.6 to 5.4 degrees F) higher than they are now, and sea levels were 25 meters (82 feet) higher. 

Equally crucially, because of those nearly equal CO2 levels, the period tells us what our world may look like all too soon.  "We studied this particular interval in unprecedented detail because it provides great contextual information for our current climate state," says Elwyn de la Vega, researcher at the University of Southampton's School of Ocean and Earth Science, in the UK, and lead author of the Nature Scientific Reports study.

The Southampton research team was able to pin down those ancient CO2 levels by studying the fossilized shells of foraminifera--millimeter-sized sea creatures protected by carbon-rich shells. The ratios of boron isotopes in the shells correlate with atmospheric CO2 levels at the time the shells formed.

Clearly, we're not going to see a return of saber-toothed cats or giant bears. But we, or our children or grandchildren, may well have to deal with a Pliocene climate--much hotter, lacking most of the Northern Hemisphere's ice cover, and with rapidly rising sea levels.

Why aren't we already living in mid-Pliocene conditions? Simply because there hasn't been time for the full impact of the greenhouse gases we've already pumped into the atmosphere to warm the oceans and melt most of Earth's ice. Geochemist Gavin Foster, also at the University of Southampton explains:

... it takes a while for Earth’s climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium.

To get a sense of what things will be like when Earth has reached that Pliocene-like equilibrium, picture your favorite coastal city under 80 feet of water. According to recent research, coastal flooding could displace hundreds of millions of people and cost the global economy trillions of dollars by the end of this century if we don't get a grip on climate change now.

Keeling curve--atmospheric CO2 1960-2020

Credit: Scripps Research Insitute

Right now we're at 413 parts per million of atmospheric CO2, and rising, and the curve is getting steeper. We're running as fast as we can towards a very inhospitable past.

--REA

ONE MORE DEGREE COULD TRIGGER A COLLAPSE OF GREENLAND'S ICE SHEET

The latest and best reconstruction of temperatures near Greenland over that last 450,000 years shows that much of Greenland's vast ice sheet could melt from sustained warming of less than one degree. That means that the world risks triggering a devastating 7 meters (23 feet) of sea-level rise before the end of this century.

 Greenland Ice Sheet at Risk

Credit: cake@cake0

Writing in the prestigious Proceedings of the National Academy of Sciences (PNAS), researchers at the University of Bergen, Norway, and at Rutgers University, New Brunswick, New Jersey, analyze 450,000 years of sea surface temperatures off the coast of Greenland. They were able to track four interglacial (warm) periods, during one of which Greenland's southern ice sheet completely disappeared. During that 30,000-year-long warm period centered around 400,000 years ago, temperatures were only slightly higher than they are today--within one degree C--and well within the projections of climate models for the end of this century--if we continue on a business-as-usual trajectory.

Comparing the four warm periods it became clear that the amount of warming was not the only factor impacting how much of Greenland's ice melted. The other key was the duration of the warming. Even with temperatures just 0.8 degrees C warmer than today, the longer duration of the warm period centered around 400,000 years ago led to almost complete melting of Greenland's southern ice sheet.

According to the authors, their findings support climate models that find a tipping point somewhere between 0.8 and 3.2 degrees C warmer than today, beyond which melting of Greenland's ice sheet is inevitable even if temperatures go back down. Paleoclimatologist Nil Irvali, at the University of Bergen, explains that the tipping point occurs when melting reduces the altitude of the ice surface to the point where the even-warmer temperatures at the lower elevation guarantees runaway melting. "The elevation effect becomes dominant over time," she says, "melting accelerates, and may even continue even though the climate cools again."

The risk, she clarifies, is not that the Greenland Ice Sheet will melt before the end of the century, but that by the end of the century atmospheric warming caused by a continuation of current policies and emissions could easily trigger irreversible melting and an eventual, and devastating, 7-meter sea-level rise.

Actually, Irvali points out, it's even worse than that, since both atmospheric carbon dioxide and warmer ocean waters have extremely long lifetimes. "It is also important to note that CO2 we put into the atmosphere will have a long lifetime even if we cut emissions, and as more and more heat accumulates in the ocean it commits us to a longer timescale of warming," she says, "So our current activities will impact climate for millennia to come."

The authors conclude, "Notably, the critical temperature threshold for past [Greenland Ice Sheet] decay will likely be surpassed this century. The duration for which this threshold is exceeded will determine Greenland's fate."

To which we must add, and the fate of millions of Americans and hundreds of millions of people worldwide.**

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**In case this paleo-historical study seems too theoretical, recent observations by a completely different set of researchers show that Greenland is losing ice 7 times faster than it was two decades ago, in line with the IPCC's worst-case scenario, putting some 400 million people at risk of coastal flooding by 2100.

REA

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TRANSLATE CLIMATE SCIENCE INTO ACTION? NOT WHILE TRUMP'S IN THE WHITE HOUSE

The researchers who leaked the National Climate Assessment in early August did so out of fear that the Trump administration would censor or simply refuse to publish the report--the product of years of work by 13 federal agencies.

Trump has already proved them right by shutting down the advisory committee charged with evaluating and translating the assessment's scientific findings into action.

It's not as though action on climate change isn't urgently needed--the assessment found that temperatures are rising rapidly, especially in the western US and the northern Great Plains; the Atlantic seaboard can expect more destructive hurricanes; California can expect more droughts; the Northeast can expect more deluges and floods; coastal cities will suffer more flooding as sea levels rise; and the risk of irreversible climate tipping points is growing.

Hurricane Isabel hits East Coast of US, 2003
Credit: Wikipedia

With Trump in the White House (or at Mar-a-Lago), and Scott Pruitt in charge of the EPA, the US will not just be ignoring climate change, it will be moving full speed in reverse.

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Click here for an update on this from Grist.

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SOUTH MIAMI BREAKS FROM CLIMATE DENIAL, MANDATES SOLAR PANELS ON NEW CONSTRUCTION

Here's a quicklink to a Cleantechnia,com story about how South Miami is coming to its senses about global warming, climate change and, especially, the region's risk from rising sea levels and storm surges. It's the first city outside of California to mandate solar panels on all new homes.

Tidal flooding on a sunny day, Miami, 2016
Credit: B137

While our leaders at the federal level continue to march backwards with respect to climate change and its impacts, cities like South Miami and states like California and New York are, of necessity, taking the lead.

SEA LEVEL RISE SPEEDING UP

Climate scientists have been concerned about the risks from rising sea levels for nearly 50 years.

That a warming climate will raise sea levels makes intuitive sense--water, including all the water in the world's oceans, expands as it warms, and melt water from glaciers, ice sheets and the Antarcitc ice cap will of course end up in the oceans.

Although the pace of sea level rise seems small, on the order of a millimeter per year, its impact is multiplied by higher tides, stronger storm surges, sea-level-rise hotspots, and by the fact that 634 million people, close to ten percent of the world's population, live in low-lying coastal areas. The US is among the top ten countries with large numbers of people at risk from sea-level rise.

Pinning down the rate of sea level rise has proved to be challenging (see "Sea level measurement" at this URL). Now, however, a team of researchers has used sophisticated statistical techniques to deal systematically with the sources of uncertainty in different sea level data sets. "This likely is the first time a group of statisticians have had really close examination of sea level data," says Andrew Parnell, at University College Dublin.

Their approach allowed them to trace sea level changes over the past 2000 years, with increasing accuracy as more, and more accurate, data have become available in recent decades.

The group found that from 1 AD through 1800 AD, global sea levels rose by much less than one millimeter per year. They began to rise more rapidly at the start of the Industrial Revolution, and are currently not just rising, but rising faster and faster. They estimate that globally the rate is now 1.7 millimeter per year.

"Some people argue that sea levels are not rising," says Parnell. "We are showing them that sea levels are not only rising, but accelerating.

In terms of potential impacts, the East Coast of the US is at particularly high risk. It happens to be one of the sea level rise hotspots. For example, sea level near New York City is rising by 3 millimeters per year, putting more than $25 billion of infrastructure at risk.

New Orleans after Hurricane Katrina

September 11, 2005

Source: NOAA

Author: Lieut. Commander Mark Moran, NOAA Corps, NMAO/AOC

Parnell and his colleagues presented their new findings at the 2017 Joint Statistical Meetings, in Baltimore, Maryland.