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To glean insights into climate change, a small clan of intrepid scientists deploys to some of the most extreme places on Earth: the Greenland and Antarctic ice sheets.

From temporary camps, they drill long cores of ice containing chemical clues about ancient climates — clues that have revealed key insights into how spaceship Earth’s climatic life support system works. 

Like other members of the ice-coring clan, Dorthe Dahl-Jensen, hopes this knowledge can ultimately help inform decisions critical to avoiding the worst possible outcomes of human-caused climate change. 

Saying the world is going under is dangerous because young people will say, ‘Why should I take an education, there is no future for me anyway.’ That has never been more wrong. Many people have shown that we can solve this problem.” — Dorthe Dahl-Jensen

Dahl-Jensen is a researcher at the University of Manitoba’s Centre for Earth Observation Science, and a Professor at the Niels Bohr Institute, the University of Copenhagen. She was recently awarded the Mohn Prize, a prestigious honor for excellence in Arctic research. 

I sat down to chat with Dahl-Jensen at the recent Arctic Frontiers conference in Tromsø, Norway, where she received the award. Joining me was a friend and fellow science journalist, Tomasz Ulanowski, a reporter for the Polish publication Gazeta Wyborcza. We both posed questions to her about what scientists are learning from studying ice. What follows is a mix of questions and answers interwoven with background information from my own reporting.

Make sure to read through to the end, where Dahl-Jensen moves beyond the science to address what she thinks it is saying about the urgent need to act on climate change. Unlike what we often hear, it is not actually a depressing or even scary message.

A dome structure is the center of life at the East Greenland Ice-core Project, or Eastgrip. Members of the ice coring team take their meals and relax inside. Scientists hope the project will improve understanding of how ice streams will contribute to future sea-level change, and also reveal new details about past climatic conditions. (Source: East Greenland Ice-core Project, www.eastgrip.org)

My colleague got things going with this question: What does the ice teach us?

She began by noting just how unusual water ice is:  “Ice is lighter than water,” she said. “There are not many other materials where the solid form is lighter than the liquid form. So it floats on the water.” 

That might not sound so special, but ice floating on water rather than sinking actually has a profound impact: It helps regulate our planet’s climate.

Arctic Sea Ice

The sun sets over the Arctic sea ice pack, as observed in October of 2014. Sea ice helps maintain cold temperatures in the Arctic. (Source: NASA/Alek Petty)

That’s because floating sea ice forms a bright shield over the Arctic Ocean and surrounding waters. That shield reflects huge amounts of solar energy back into space — energy that otherwise would warm the region. This helps maintain frigid conditions in the high north. 

But human-caused warming has caused this reflective shield of floating sea ice to shrink at a rate of 12.85 percent per decade since 1979, as measured every September. (This is when the ice reaches its yearly lowest extent at the end of summer.) Studies suggest that since the late 20th century, the decline in summer Arctic sea ice has been steeper than at any time in the past 1,450 years.

Arctic sea ice delinks

This graph shows how the extent of Arctic sea ice has departed from monthly means between January 1953 and December 1979. For January 1979 to the present, data have been derived from satellite sensors. The record prior to 1979 is based on operational ice charts and other sources. (Image by Walt Meier and Julienne Stroeve, National Snow and Ice Data Center, University of Colorado, Boulder.)

As sea ice shrivels, more and more solar energy is being absorbed by the relatively dark ocean surface rather than being reflected back to space. The result: The Arctic has warmed twice as much as any other region on Earth, a phenomenon scientists call “Arctic amplification.” 

The fact that ice floats on the surface of the sea also makes it “super fundamental — because it shields the life in the ocean,” Dahl-Jensen told us. 

At the base of life’s food web in Arctic waters are phytoplankton. As winter turns to spring and temperatures naturally warm, sea ice thins, breaks up and and finally melts, providing phytoplankton with the solar energy they need to grow. Springtime blooms of phytoplankton are grazed on by animals known as zooplankton. Arctic species are relatively big and fatty, providing the Arctic cod that feed on them a lot of energy per bite. The cod are in turn eaten by seals, which are the favorite meal of polar bears. 

As the Arctic has warmed, the shield of sea ice has thinned and broken up earlier, in turn causing earlier blooms of phytoplankton. This is sending impacts rippling up the Arctic marine food web. For example, there is evidence that the Arctic zooplankton are being replaced by more southerly, less nutritious species. And more southerly fish species seem to be migrating northward. 

Thinning sea ice has allowed more sunlight to reach the water right beneath the ice, triggering blooms of phytoplankton earlier than in the past.

Scientists say that a huge shift in Arctic marine ecosystems may be in the offing, but they are not yet sure what the outcome will be. As Dorothy Dankel, a fisheries scientist at Norway’s University of Bergen, put it to me for a feature story I wrote not long ago, “It’s a fascinating, complex, perfect storm. It can either come out really great, or everything could go down the shithole.”

Shifting to a different aspect of Arctic ice during our interview with Dahl-Jensen, my colleague asked this: What can it teach us about Earth’s history?

Dahl-Jensen has long studied the chemical and other clues trapped within cores of ice drilled from the Greenland ice cap in order to gain insights into past climates. The hope is that those insights can help us see better what the future holds as we continue to pump carbon dioxide and other heat-trapping greenhouse gases into the atmosphere. 

Dahl-Jensen noted that every year’s snowfall on the ice cap “creates a layered record. It is very much like tree rings,” she said. “You get a layer from each year.” And each annual layer of snow eventually compresses into ice, trapping climatic clues within it.

Volcanic Ash Layer in West Antarctic Ice Core

The dark band in this layered ice core from the West Antarctic Ice Sheet Divide is volcanic ash that settled on the ice sheet about 21,000 years ago. (Source: Heidi Roop, NSF)

“On the Greenland Ice Sheet we get climate information going 200,000 years back in time,” she said. “At the bottom, we also find material that is 1 million years old.”

In Antarctica, Dahl-Jensen noted that the layered ice record goes back more than 800,000 years. “We are hoping for 1.5 million years, and we even believe that it must be at least 5 million years in places,” she said.

“We use ice as a history book,” she said. “That’s what fascinates me.”

That history book contains information about the makeup of the atmosphere in millennia past. When snow falls to the surface and is then covered by yet more, it eventually turns to ice under the overlying pressure. Air that was trapped between the snowflakes is then preserved, first in bubbles and then within the matrix of ice crystals. Going back layer-by-layer, and thus year-by-year, scientists can recover that air and determine how much carbon dioxide, methane and other gases were present in the past. 

1280px-CSIRO ScienceImage 521 Bubbles in Ice

Tiny bubbles of air are evident in this sliver of Antarctic ice. Air bubbles like this provide vital information about past concentrations of greenhouse gases in the Earth’s atmosphere.(Source: CSIRO via Wikimedia Commons)

The icy history book also contains information about the temperatures that prevailed when the snow first fell. This information comes in the form of chemical fingerprints corresponding to warmer or cooler conditions in the clouds from which the snow fell. 

“We can also measure dust particles in the ice, wind-blown dust,” Dahl-Jensen said. “The dust we find in the Greenland ice cores mainly comes from China. So it moves a long way. And we can measure how much dust is present. This is a function of how dry it was in China, and also a function of how strong the storms were that moved the dust to Greenland.”

In the end, scientists can measure about “10 different parameters with annual resolution. We use all these 10 parameters to date the core. So we simply count — one year, summer and winter, another year, summer and winter. And we can go thousands of years back in time. This gives just a gold mine of climate information,” Dahle Jensen said.

“What we see in ice cores, and what is also supported by geological records that go further back, is that every time we’ve had high values of CO2, we’ve had warm temperatures,” she said. “So there has always been a strong correlation between CO2 and surface temperature. It is surprising that people can doubt whether the high values of greenhouse gases now will result in warmer temperatures once our system adjusts to the vastly changing values.”

Temperature and CO2 from the Epica Ice Core

Carbon dioxide in the atmosphere has corresponded closely with temperature over the past 800,000 years, as seen in these data from the EPICA ice core drilled from Antarctica. Although the temperature changes were touched off by variations in Earth’s orbit, the increased global temperatures released CO2 into the atmosphere, which in turn warmed the Earth. (Source: NASA Earth Observatory.)

Dahl-Jensen is getting at an aspect of climate change that’s not widely appreciated. Yes, global average temperature has already risen by about 1 degree C thanks to emissions of greenhouse gases so far. But if we were to shut off emissions tomorrow, we would not forestall further warming completely. Far from it, in fact. We’d still see much more warming.

That’s because the oceans, which have been absorbing more than 90 percent of the heat that has built up, produce a lot of inertia in the climate system. This stems from two physical facts: It takes a long time for heat to fully warm the oceans, and also a long time for that heat to come out and warm air temperatures.

Global Warming Heat

Source: Rosamund Pearce, Carbon Brief: https://www.carbonbrief.org/heat-absorbed-by-oceans-has-doubled-since-1997)

Here’s how Dahl-Jensen explained it:

“We have a system that is totally out of balance now. The system doesn’t react from day to day. The surface of the sea does, but the ocean as a whole doesn’t. That’s because warming the deep ocean takes place on the scale of a thousand years. So we have a system that takes a thousand years to get into balance. And that means we have a strongly imbalanced system now. As a result we haven’t seen the warming you’d expect from the CO2 we have already put in the atmosphere.”

How much additional warming can we expect?

“I would say two degrees,” Dahl-Jensen said. “But I wouldn’t listen to that if I were you, because there are so many things we do not know.” 

Among them: details about what happens to carbon that gets absorbed into the ocean. 

“The carbon cycle is probably one of the most difficult balances to make,” Dahl-Jensen said. “How does the ocean do this uptake?” Thanks to absorption of carbon dioxide into ocean waters, “we see that the ocean is becoming more acid. This reduces its ability to take up more CO2.” 

Ocean Acidification

About half of the CO2 that has been pumped into the atmosphere since the dawn of the industrial era has been absorbed by the oceans through natural processes, making them more acidic. This harms marine ecosystems, including coral reefs. (Source: John MacNeill, Climate Central: https://www.climatecentral.org/gallery/graphics/ocean-acidification-process)

In other words, the ocean has been doing us a favor by absorbing CO2 that otherwise would have warmed the globe. (But we haven’t been doing the oceans and marine organisms a favor because that CO2 is causing acidification — see the graphic above.)

How much more can we depend on the ocean to absorb lots of CO2? Scientists aren’t sure.

I then turned our conversation toward the idea of climatic tipping points. Many scientists say we have about 10 years left to avoid crossing a catastrophic threshold. But how do we reconcile that idea with the fact that we may have hundreds of years of further warming in the pipeline no matter what we do?

“I don’t really like this,” Dahl-Jenssen said. “I’m not fond of these dramatic ways of presenting things . . . I think the word tipping point is very often misused, because in my opinion, tipping point means if you reverse the process you won’t get back to the same point again. I think if we reduce the CO2 we would actually get back to the same point again.”

She also says the tipping point argument prevents people from taking action. “I think it scares people more than it tells them that we are in a world of opportunities, and [climate change] is something we can solve. We just have to take it seriously and get cracking. We should tell all our young people that this is the most important thing in the world, that we need a super-skilled set of people who can help us solve it in the future. I think that would be a much, much more valuable point of view than telling people that the world will go under in 10 years.”

Young people, like the Norwegian climate activist, Greta Thunberg, are already stepping up, Dahl-Jensen observed. “They are saying, ‘Hey, come on, leave a world for us, we don’t have a Planet B.’ That is just amazing,” Dahl-Jensen said. 

“But I think saying the world is going under is dangerous because young people will say, ‘Why should I take an education, there is no future for me anyway.’ That has never been more wrong. Many people have shown that we can solve this problem — we can stop the emissions of greenhouse gases, we can easily go to green energy, and we can also live with a world that becomes warmer.”

Even so, there will be big challenges, Dahl-Jensen acknowledged. One is that many people will have to migrate from parts of the globe that will become impossible to live in thanks to sea level rise, soaring temperatures and other impacts.

“We have to be more tolerant of movement of populations,” she said. “We can’t allow people to go into war every time some people have to move . . . We have to say, ‘Yes, you’re right, you can’t live there, it’s underwater, or too dry.’ We have to allow for movement.” 

Dahl-Jensen pointed out that water shortages helped ignite the conflict in Syria that sent many refugees streaming into Europe. “Syria was the first climate change war we’ve had,” she said. 

Unless we begin to plan for the inevitable increases in sea level and severe heat and drought that are coming, more wars fomented by climate change will be in the offing, she argued.

At the end of our conversation, Dahle-Jensen reflected on how difficult it is for scientists to help prompt positive action like that.

She related an incident in which a foreign minister once accused her and other scientists of hampering action by not providing definitive answers. “‘How can you expect us to respond when you say something different every day?'” she recalls him saying. In her view, that reflected a fundamental misunderstanding of how science actually works.

“We are not saying something different every day, but we are always upgrading our knowledge,” Dahl-Jensen told us. “So I answered him back: ‘Why didn’t you predict the financial crisis? Because you know, it’s kind of a similar complex system that people can’t predict. ‘He got so furious he said, ‘Dorthe, I’ll never give you a grant again.’” 

It didn’t actually pan out that way. “He did calm down,” she says.



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