Thursday , June 24 2021

The Arctic hasn’t been so hot for 3 million years

A block of ice drifting in Svalbard, Norway. Image via Sven-Erik Arndt / Arterra / Universal Images Group / Getty images

to Julie Brigham-Gret, University of Massachusetts Amherst and Steve fetch, University of Massachusetts Amherst

Each year, sea ice in the Arctic Ocean decreases to minimum levels in mid-September. This year, it is only 3.44 million square miles (3.7 million square kilometers). Second lowest value Today, 42 years after satellites started measuring, ice has been 50% of the area 40 years ago. Late summer.

This year’s minimum ice cover is the lowest in a satellite record of 42 years, excluding 2012, reinforcing the long-term downward trend in Arctic ice cover. Summer sea ice has declined on average over the past 40 years. Image via NSIDC / conversation

As the intergovernmental panel on climate change shows, the level of carbon dioxide in the atmosphere is higher than ever in human history. Finally, when the concentration of CO2 in the atmosphere reaches the current level About 412 ppm – That was 3 million years ago. During the Pliocene era. That said, the Arctic hasn’t been that hot for 3 million years.

As a scientist researching the evolution of Earth’s climate and how to create living conditions, we see changes in Arctic conditions as an indicator of how climate change can change the planet. The continued increase in global greenhouse gas emissions could bring the planet back to the state of Pliocene, where sea levels are higher, weather patterns change and conditions have changed in both places. Natural world and human society.

Arctic Pliocene

We are part of a team of scientists who analyzed the core of the sediment. Lake El Giggin In 2013, in northeastern Russia, we understood the arctic climate with high levels of carbon dioxide in the atmosphere. The fossil pollen preserved in this core shows that the Pliocene Arctic is very different from its current state.

Today the Arctic is a plain without trees and Tundra plants, such as grass, reeds and some flowering plants. In contrast, the Russian sedimentary core Pollen from trees such as larch, spruce, fir and hemlock. this is the boreal forest. Today, it reached the Arctic Ocean in most of Arctic Russia and North America, ending hundreds of kilometers further south and west of the Arctic Circle in Russia and Alaska today.

The Arctic was much hotter in the Pliocene, so the Greenland ice sheet did not exist. The small glacier along Greenland’s mountainous east coast was one of the few places in the Arctic with ice year-round. In the Earth’s Pliocene, there was ice only at one end of Antarctica, and that ice was less wide and more susceptible to melting.

Northern forest near Lake Baikal, Russia. Three million years ago, this forest stretched hundreds of kilometers to the north of what arrives today. Through the image Christophe Meneboeuf / Wikipedia

As the seas were warmer and there were no large ice sheets in the northern hemisphere, sea levels were 9 to 15 meters higher worldwide than they are today. The coast was inland, far from its current location. Today, the Central Valley of California, the Florida Peninsula and the Gulf Coast region are all underwater. The same happened with the lands where the main coastal cities were, such as New York, Miami, Los Angeles, Houston and Seattle.

Winters in the western United States are now warmer. It provides a lot of water in this area. Today, the Midwest and the Great Plains are much hotter and drier to plant corn or wheat there, it would be impossible.

Why was there so much CO2 in the Pliocene?

How did the CO2 concentration during the Pliocene reach levels similar to today? Humans will not appear on Earth for at least a million years, and our use of fossil fuel is much more recent. The answer is that some natural processes on Earth release CO2 into the atmosphere, while others consume it. The main system that balances this dynamic and controls the Earth’s climate are the Earth’s natural thermostats controlled by rocks. Reacts chemically with CO2. Remove it from the atmosphere.

The greenhouse effect increases the surface temperature and in some areas the rain. Together, they accelerate the wear of silicate rocks. Faster weathering removes more CO2 from the atmosphere (yellow arrow). The intensity of the greenhouse effect depends on the level of atmospheric CO2. Image via Gretashum / Wikipedia / Conversation

Certain soil rocks are constantly decomposed into new substances in reactions that consume CO2. These reactions tend to accelerate when temperatures and rainfall are highest. It corresponds exactly to the climatic conditions that arise when the concentration of greenhouse gases in the atmosphere increases.

But this thermostat has built-in control. As CO2 and temperature increase and the wear and tear on rocks accelerates, it removes more CO2 from the atmosphere. When CO2 starts to fall, temperatures decrease, the wear and tear of rocks globally decreases and emits less CO2.

Rock weathering reactions can work faster even where the soil contains many newly exposed mineral surfaces. For example, it includes areas of strong erosion or periods when the processes of the earth’s crust push the soil upwards, creating a large mountain range with a steep slope.

Rock weathering thermostats operate at a geologically slow rate. For example, at the end of the dinosaur era, some 65 million years ago, scientists estimate that atmospheric CO2 levels are between 2,000 and 4,000 ppm. It took more than 50 million years to naturally reduce to about 400 ppm in the Pliocene.

As natural changes in CO2 levels occurred very slowly, periodic changes in the global climate system were also very slow. Ecosystems have taken millions of years to adapt, adjust and respond slowly to climate change.

Summer heat waves transform northern Siberia, melt permafrost and create conditions for major forest fires.

Future like the Pliocene?

Human activity today overcomes the natural process of releasing carbon dioxide from the atmosphere. At the beginning of the industrial era in 1750, atmospheric CO2 was around 280 ppm. It took only 200 years for humans to completely reverse the orbit that started 50 million years ago and return the Earth to levels of CO2 that have not been experienced in millions of years.

Most of these changes have occurred since World War II. Currently, annual increases of 2-3 ppm are common. In response, the planet is warming up at a rapid pace. Since about 1880, the Earth has been 2 degrees Fahrenheit (1 degree Celsius) – many times faster than any warming event in the last 65 million years of Earth’s history.

In the Arctic, this warming has been increased to 9F (+ 5C) due to the loss of reflected snow and ice. As a result, the variation in Arctic sea ice in the summer is decreasing. Scientists say the North Pole Without ice in the summer In the next 20 years

This is not the only evidence of extreme arctic warming. Dissolution rate of scientists in the extreme summer in the Greenland ice sheet. In early August, in the territory of Nunavut, Canada’s last remaining ice shelf fell into the sea. ~ formerly Arctic Siberia and SvalbardThe Norwegian island group in the Arctic Ocean reached record levels this summer.

When this planet returns to the Pliocene CO2 world, the water supply of coastal cities, areas of agricultural craters and many communities will be radically different. This future is not inevitable. However, to avoid this, major steps are needed to reduce the use of fossil fuels and lower the global thermostat.

Julie Brigham-Gret, Professor of Earth Sciences, University of Massachusetts Amherst and Steve fetch, Associate Professor of Earth Sciences, University of Massachusetts Amherst

This article was republished under: Conversation Under Creative Commons License. read the original article.

In short: the Arctic hasn’t been that hot for 3 million years. These geoscientists discuss what is happening in the Arctic and how it will affect the rest of the world.


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