{"id":22317,"date":"2020-10-04T23:52:48","date_gmt":"2020-10-04T23:52:48","guid":{"rendered":"https:\/\/www.lifeandnews.com\/articles\/?p=22317"},"modified":"2020-10-06T12:39:59","modified_gmt":"2020-10-06T12:39:59","slug":"the-arctic-hasnt-been-this-warm-for-3-million-years-and-that-foreshadows-big-changes-for-the-rest-of-the-planet","status":"publish","type":"post","link":"https:\/\/www.lifeandnews.com\/articles\/the-arctic-hasnt-been-this-warm-for-3-million-years-and-that-foreshadows-big-changes-for-the-rest-of-the-planet\/","title":{"rendered":"The Arctic hasn’t been this warm for 3 million years \u2013 and that foreshadows big changes for the rest of the planet"},"content":{"rendered":"

Julie Brigham-Grette<\/a>, University of Massachusetts Amherst<\/a><\/em> and Steve Petsch<\/a>, University of Massachusetts Amherst<\/a><\/em><\/p>\n

Every year, sea ice cover in the Arctic Ocean shrinks to a low point in mid-September. This year it measures just 1.44 million square miles (3.74 million square kilometers) \u2013 the second-lowest value<\/a> in the 42 years since satellites began taking measurements. The ice today covers only 50% of the area it covered 40 years ago<\/a> in late summer.<\/p>\n

\"Graph<\/a>
This year\u2019s minimum ice extent is the lowest in the 42-year-old satellite record except for 2012, reinforcing a long-term downward trend in Arctic ice cover. Each of the past four decades averages successively less summer sea ice.<\/span>
\nNSIDC<\/span><\/span><\/figcaption><\/figure>\n

As the Intergovernmental Panel on Climate Change has shown, carbon dioxide levels in the atmosphere are higher than at any time in human history<\/a>. The last time that atmospheric CO2 concentrations reached today\u2019s level \u2013 about 412 parts per million<\/a> \u2013 was 3 million years ago, during the Pliocene Epoch<\/a>.<\/p>\n

As geoscientists who study the evolution of Earth\u2019s climate<\/a> and how it creates conditions for life<\/a>, we see evolving conditions in the Arctic as an indicator of how climate change could transform the planet. If global greenhouse gas emissions continue to rise, they could return the Earth to Pliocene conditions, with higher sea levels, shifted weather patterns and altered conditions in both the natural world<\/a> and human societies<\/a>.<\/p>\n

The Pliocene Arctic<\/h2>\n

We are part of a team of scientists who analyzed sediment cores from Lake El\u2019gygytgyn<\/a> in northeast Russia in 2013 to understand the Arctic\u2019s climate under higher atmospheric carbon dioxide levels. Fossil pollen preserved in these cores shows that the Pliocene Arctic was very different from its current state.<\/p>\n

Today the Arctic is a treeless plain with only sparse tundra vegetation<\/a>, such as grasses, sedges and a few flowering plants. In contrast, the Russian sediment cores contained pollen from trees such as larch, spruce, fir and hemlock<\/a>. This shows that boreal forests<\/a>, which today end hundreds of miles farther south and west in Russia and at the Arctic Circle in Alaska, once reached all the way to the Arctic Ocean across much of Arctic Russia and North America.<\/p>\n

Because the Arctic was much warmer in the Pliocene, the Greenland Ice Sheet did not exist. Small glaciers along Greenland\u2019s mountainous eastern coast were among the few places with year-round ice in the Arctic. The Pliocene Earth had ice only at one end \u2013 in Antarctica \u2013 and that ice was less extensive and more susceptible to melting<\/a>.<\/p>\n

\"Forest<\/a>
Boreal forest near Lake Baikal in Russia. Three million years ago these forests extended hundreds of miles farther north than they reach today.<\/span>
\nChristophe Meneboeuf\/Wikipedia<\/a>, CC BY-SA<\/a><\/span><\/figcaption><\/figure>\n

Because the oceans were warmer and there were no large ice sheets in the Northern Hemisphere, sea levels were 30 to 50 feet (9 to 15 meters) higher around the globe than they are today. Coastlines were far inland from their current locations. The areas that are now California\u2019s Central Valley, the Florida Peninsula and the Gulf Coast all were underwater. So was the land where major coastal cities like New York, Miami, Los Angeles, Houston and Seattle stand.<\/p>\n

Warmer winters across what is now the western U.S. reduced snowpack, which these days supplies much of the region\u2019s water<\/a>. Today\u2019s Midwest and Great Plains were so much warmer and dryer that it would have been impossible to grow corn or wheat there.<\/p>\n

Why was there so much CO2 in the Pliocene?<\/h2>\n

How did CO2 concentrations during the Pliocene reach levels similar to today\u2019s? Humans would not appear on Earth for at least another million years, and our use of fossil fuels is even more recent. The answer is that some natural processes that have occurred on Earth throughout its history release CO2 to the atmosphere, while others consume it. The main system that keeps these dynamics in balance and controls Earth\u2019s climate is a natural global thermostat, regulated by rocks that chemically react with CO2<\/a> and pull it out of the atmosphere.<\/p>\n

\"Diagram<\/a>
The Greenhouse Effect leads to increases in surface temperatures and, in some places, rainfall. Together these accelerate silicate rock weathering. Faster weathering in turn removes more CO2 from the atmosphere (yellow arrow). The strength of the Greenhouse Effect relies on atmospheric CO2 levels.<\/span>
\nGretashum\/Wikipedia<\/span><\/span><\/figcaption><\/figure>\n

In soils, certain rocks continually break down into new materials in reactions that consume CO2. These reactions tend to speed up when temperatures and rainfall are higher \u2013 exactly the climate conditions that occur when atmospheric greenhouse gas concentrations rise.<\/p>\n

But this thermostat has a built-in control. When CO2 and temperatures increase and rock weathering accelerates, it pulls more CO2 from the atmosphere. If CO2 begins to fall, temperatures cool and rock weathering slows globally, pulling out less CO2.<\/p>\n

Rock weathering reactions also can work faster where soil contains lots of newly exposed mineral surfaces. Examples include areas with high erosion or periods when Earth\u2019s tectonic processes pushed land upward, creating major mountain chains with steep slopes.<\/p>\n

The rock weathering thermostat operates at a geologically slow pace. For example, at the end of the Age of Dinosaurs about 65 million years ago, scientists estimate that atmospheric CO2 levels were between 2,000 and 4,000 parts per million. It took over 50 million years to reduce them naturally to around 400 parts per million in the Pliocene.<\/p>\n

Because natural changes in CO2 levels happened very slowly, cyclic shifts in Earth\u2019s climate system were also very slow. Ecosystems had millions of years to adapt, adjust and slowly respond to changing climates.<\/p>\n