Half A Degree Celsius Could Make A Big Difference For Arctic Sea Ice

By Tom Yulsman | April 9, 2018 2:27 pm

Two independent studies show how much we need to limit warming to preserve the ice. But we’re currently headed on a very different path.

Sea ice in the Chukchi Sea. A small difference in global warming could help determine whether sea ice would disappear or not.

The U.S. Coast Guard Cutter Healy encountered only small patches of sea ice in the Chukchi Sea when this photograph was taken on July 20, 2011. (Courtesy NASA Goddard Space Flight Center)

Almost every month now we get news of dramatic losses of Arctic sea ice due to human-caused warming — and last month was no exception. The ice extent in March 2018 turned out to be the second lowest for the month in the satellite record.

The best estimates are that unless we significantly reduce our emissions of planet-warming carbon dioxide, the Arctic Ocean will begin to experience ice-free summers by mid-century, if not sooner.

But just how much would it take to give the ice a fighting chance? According to a pair of independent modeling studies published in the journal Nature Climate Change, a global warming difference of just a half degree Celsius — that’s less than a degree Fahrenheit — could make all the difference.

Both studies examined what would happen if humankind managed to restrain global warming by the end of the century to no more than 1.5 degrees C (2.7 degrees Fahrenheit), versus 2 degrees C (3.6 degrees Fahrenheit).

Those different levels of warming are significant because of the Paris Climate agreement. It commits the 175 signing parties to exerting their best efforts at keeping global warming this century below 2 degrees C above preindustrial levels. The agreement also states that it would be much preferable to limit warming no more than 1.5 C.

The two new studies show for the first time just how beneficial achieving the lower number would be for the Arctic, out to the year 2100.

As University of Colorado climate scientist Alexandra Jahn, the author of one of the studies, put it to me in an interview, “There’s a strongly reduced probability of experiencing ice-free summers if warming can actually be limited to one and a half degrees instead of two.”

The other study, conducted independently by Canadian researchers, produced the same overarching insight.

“We arrive at very much the same conclusions,” Jahn said. “This tells us that we can trust results.”

If you’re wondering why we should care about the Arctic, the answer involves more than polar bears, Arctic ecosystems, fisheries, undiscovered resources, and geopolitics. What happens in the Arctic doesn’t stay in the Arctic.

Russian flag on the seafloor at the North Pole. A small difference in global warming could determine whether Arctic sea ice disappears or not.

In 2007, Russia used a pair of submersible vessels to plant the nation’s flag on the seabed at the North Pole. It was a symbolic gesture in support of Russia’s disputed claim to nearly half of the Arctic Ocean seafloor — and potential oil and gas resources there. (Photo: Still from NTV Russian State Television)

“Everything that happens in the climate system is connected,” Jahn said. Although the details are still being investigated, warming in the Arctic and losses of sea ice appear to have impacts on mid-latitude weather. Moreover, losing the sea ice in summer is likely to “further accelerate global warming in general.”

In Jahn’s study, simulations run on the Community Earth System Model, or CESM, showed that global warming of about 2 degrees C would guarantee ice-free conditions in summer by the year 2100. Moreover, “frequent ice-free conditions can be expected, potentially for several months per year,” she writes in her paper.

By contrast, if we were to limit our emissions of CO2 enough to constrain warming to no more than 1.5 °C, the probability of ice free conditions occurring by 2100 would drop to just 30 percent.

Jahn did not expect that big of a benefit.”I was surprised by that,” she said in our interview.

Why would such a relatively modest change make such a big difference? When I put that question to Jahn she pointed out that “nobody exists in the global mean climate.” Some areas of the world are heating up more quickly than the global average — and none more so than the Arctic.

Global temperatures anomalies for 2007-2017. A small difference in global warming could help save Arctic sea ice.

This map shows how temperatures varied from the long-term mean for the 10 years spanning 2000 through 2017. The red and orange tones in the far north show that the Arctic has been warming more than any other major region. (Source: NASA GISTEMP)

As we get further into the 21st century, that phenomenon is expected to continue, and perhaps even intensify. “Based on the model I am working with, the CESM, it seems that Arctic change is about three times as much as the global average,” Jahn said.

Emphasis on the word ‘about.’ According to her CESM modeling, here’s how the numbers work out a bit more precisely (with all temperatures given in Celsius): 1.5 degrees of global warming translates to 4.25 in the Arctic. And 2 degrees C globally means 6 degrees of warming in the Arctic. That’s why a seemingly small difference can help save the ice.

But that doesn’t mean Arctic sea ice will stop shrinking. “Even when warming is limited to 1.5 °C, the Arctic summer sea-ice cover experiences significant reductions compared to today’s cover,” Jahn writes in her paper.

Also, keep in mind that this is all about probabilities. So it’s still possible that we’d see an ice-free summer — even as early as mid-century — with no more than 1.5 degrees C of warming. It’s just not a likely outcome.

Jahn’s simulations show that this would be the result of natural variation combining with the effects of human-caused warming to drive sea ice that low. But if this should happen despite the low odds “it is likely to be an isolated event, whereas in the stronger-warming scenarios a second ice-free year would soon follow the first,” Jahn writes.

One stronger-warming scenario run by Jahn on the computer model is known as “RCP8.5.” You can think of it as business as usual. With it, the concentration of carbon dioxide in the atmosphere would continue to rise steeply, and by the end of the century it would soar to above 1,000 parts per million. We’re at about 410 ppm now.

With RCP8.5, mean global warming would exceed 4 degrees C above preindustrial levels by 2100. If Jahn’s computer simulations are accurate, that would produce a truly huge increase for the Arctic — close to 12 degrees C. And the impact on sea ice would be stark.

With this scenario, “the ice-free season in the Arctic could extend from July to November in some years, with a 100% probability of ice-free conditions from August to November by the final decade of the twenty-first century,” Jahn writes.

For the second study, Canadian researchers used a different climate model and approach. Yet here too, the simulations show substantial benefits for stabilizing global warming at the end of the century at 1.5 degrees C versus 2: “an eightfold decrease in the frequency of ice-free conditions is expected, from once in every five to once in every forty years,” the scientists write.

Both studies give us something to shoot for. But we are currently headed on a different path, with CO2 concentrations still growing, and the rate of growth increasing.

If the signatory nations to the Paris Agreement really do live up to their commitments to cut greenhouse gas emissions, we’ll get onto a better path. But even so, those emission cuts would not be sufficient to limit warming to 2 degrees C, let alone 1.5. Instead, the globe overall would probably experience warming of about 3 degrees C by 2100.

With that amount of warming, the Canadian study shows that “permanent summer ice-free conditions are likely, which emphasizes the need for nations to increase their commitments to the Paris Agreement.”

How likely are we to limit global warming enough to save the Arctic sea ice? I posed that question to Mark Serreze, director of the National Snow and Ice Data Center. The NSIDC crunches the satellite-monitoring data every month to provide regular updates on what’s happening to the ice.

“If we got a handle on fossil fuel emissions, we could keep global warming from getting out of hand,” he wrote in an email message. But he’s not optimistic. “I think we are destined for a seasonally ice free Arctic Ocean. I don’t see that this is stoppable given our dependence on fossil fuels. We’ll need to adapt. And we will.”

But now that we know how much of a benefit could be gained by shooting just a little lower than 2 degrees C, perhaps we can summon up the will to do more than simply adapting and instead get more serious on mitigating the CO2 pollution that we’re pouring into the atmosphere.

  • eric

    can’t until all this artic sea ice melts and the oil companies can start extracting the oil from underneath the surface…..bring back $2.00 a gallon gas!

    • Not_that_anyone_cares, but…

      Gasoline is obsolescent.

    • Mike Richardson

      Yeah, who cares about future generations, right? 😏 [sarcasm]

      • TLongmire

        You checked the news today?who cares is right{logic}

        • Mike Richardson

          Nihilism is not logical.

          • TLongmire

            Only way to fix it is flush it all away. True morality!

      • eric

        LOl, liberals love “useful idiots” like you. Provide proof that burning fossil fuels will harm future generations…you see I believe in something greater than scientist, God.

        • Mike Richardson

          Yep, name calling and appeals to the supernatural. Looks like there’s no point in attempting reason here, as it isn’t the method of thought you’ve employed to reach this point.

          • eric

            Haha, “useful idiot” isn’t the name I came up for you, it is the name the leftist leaders came up for you and of course they didn’t believe in God. I see you have no proof, looks like your leftist idols where right about you..also I wasn’t looking for reasoning, I was looking for proof……try again….

          • Mike Richardson

            Proof of what? You’ve asked no questions. I have a few of my own, such as: What does religious belief have to do with science? Why do you think your political bias is reflected by an opposing bias in the conduct of scientific research?

          • eric

            You are the one who insulated future generations would be harmed by extracting fossil fuels from the earth, provid proof? I said i believe in a higher power and that is God. It has everything to do with it, you ever heard of the sermon on the Mount, where Jesus says that God provides for even the birds in the sky? I trust that God will take care of me/us, where you worrry about future generations being harmed….so a belief in God over man has everything. For many liberals politics is their religion, you ever hear of “hope and change”, my hope is in Jesus not a politician (man).

          • Mike Richardson

            I ” insulated future generations “? That’s a new one.

            As for proof that fossil fuels are harmful — you ever hear of Deepwater Horizon? I sure have, since I live in Louisiana. No divine intervention prevented that disaster, nor will it prevent humanity from suffering self-inflicted losses from the effects of a warming planet. The proof of that is well documented by researchers in the field of climatology, and is frequently explained in this blog. If your religious and political views prevent you from considering such objectively, well, that’s a shame.

            Food for thought — if your Christian beliefs are a factor in your views on the environment, you might want to consider the good stewardship position. Simply put, it’s the concept that man was given the earth as a gift from God, to be taken care of, and not abused or squandered. For many modern Christians, this forms the foundation of their support for environmental protection, not admiration for a particular politician.

          • eric

            good Stewardship would be providing cheap forms of energy to allow people to keep as much of their own money as possible, period. This would be accomplished by creating a greater supply of fossil fuels which are used to power the world. By limiting the God given resources, the folks that are harmed the most are those who are poor. Wow, you really are a simpleton………

          • Mike Richardson

            You’re deliberately trying for irony here, right?

          • eric

            Lol, are you refuting increased supply brings down the price of a commodity? Do you deny when commodity prices increase the ones who are harmed the most are the poor? Did they not teach you economics at your school or have you not made it that’s far in your education, Junior?

          • Mike Richardson

            Maybe my education is incomplete. I’m still waiting for you to explain what “insuiated” means, or how you figure fossil fuels (which are finite) can provide a greater supply of energy than solar or wind power (which won’t run out). Please impress me with your brilliance, as you have impressed me with your display of Christian humility and kindness. 😏

          • eric

            It is called a typo, sir. Whether a resource is finite or not has little to do with the cost of extraction…i actually feel bad for you if your education is incomplete because if you are going to rely on the traditional education centers your education will be incomplete. Our so called, centers of learning have become nothing more than indoctrination centers. If you are really interested in gaining more knowledge may I suggest you start watching videos from Prager Universtiy. You will learn more from these videos in 4 weeks than you will in 4 years from a traditional learning center.

            I’m not sure if you believe in Jesus or not but, know that he chose, to die for your sins so you may gain eternal salvation.

          • lindsncal

            Eternal salvation is disappearing before your eyes and you’re ignoring it. And..he did not chose to die for it. Some day, actually read the bible…or ask an atheist what’s in it.

          • lindsncal

            Those god given resources ARE limited. The earth is a living entity and….every living thing developes defense mechanisms. The earth will too and will fight back against whatever is harming it…after your god told you to take care of and protect it, you seem to favor its destruction.

          • lindsncal

            Tell that to the already millions of poor people around the world who are now ‘climate refugees’ because they’ve lost their homes and ability to grow their food…who now are suffering with nowhere to go.
            How is your god treating them?

          • eric

            Additionally, my original post provided reasoning, drill more for cheaper gas prices..

          • Mike Richardson

            At the expense of accelerating further warming. Not such a bargain.

        • Tom Yulsman

          Eric: One more ad hominem attack, however mild, and you are gone. You will not call anyone here an “idiot,” useful or otherwise. You will not refer derisively to anyone here as “junior.” You will also not rant about things like “leftist idols” Lastly, this is a science magazine, not a place for political and religious diatribes. So please stick to science. If you don’t like what I write about science here, please go somewhere else.

          • eric

            Wow, must of struck a nerve….for 30 years people like yourself have been trying to scare others with your fake news about global warming, climate change crap….it isn’t working nobody cares because they know what you are selling isn’t true…don’t take my word for it, take a look at public opinion polls and you will realize how unimportant what you write is to the general public ….this isn’t science it is propaganda.

          • Tom Yulsman

            Eric: You have struck nothing. I am simply trying to maintain standards at my blog. In doing that I will not tolerate ad hominem attacks, as in calling people “idiots” when in reality the issue is simply that you disagree with them. I don’t proscribe very much here, but that kind of nonsense is not allowed. Stick to the issues, or go away.

          • Tom Yulsman

            Eric has now been banned from the site because he could not stop himself from attacking people with whom he disagrees. His latest diatribe — an attack on me, comparing me to Hitler, Stalin and Mao — was caught by Disqus because of his use of restricted words. That was the last straw.

          • FreethinkingWorldGuy

            Thank you! Bravo!

          • Tom Yulsman

            In the past I have erred on the side of fewer restrictions in the comments section, rather than more. But the ever-increasing vituperation, hate and out and out idiocy that manifests itself here has become so discouraging that my threshold for banning people has dropped significantly recently. I no longer have any patience for hateful — and hypocritical— people like Eric.

          • lindsncal

            This is not a left/right thing that your sources must have told you it was.
            You and a very very very few others are the only people in the entire world who deny climate change….left or right.
            Seems your sources are full of hate and childish insults…. and don’t try and tell me that comes from god.

        • lindsncal

          Here’s some: Fourth National Climate Assessment – mandated by Congress:
          With people like you in the country, we’ll end up burning witches at the stake again.
          Stick to name calling. It seems to be the only thing you’ve learned from your god.

          • FreethinkingWorldGuy

            “[name-calling] seems to be the only thing you’ve learned from your god.”

            I agree wholeheartedly with your sentiment, but there’s a nuance worth considering: god-belief subscribers like eric don’t learn anything from “their god.” To the point, they possess god-beliefs, but to say “his god” or “their god” ascribes credit where it is NOT due. In other words, such verbiage–subtly, yet importantly–presupposes that his/their god DOES exist, which is dubious at best.

            So suggested verbiage to address this in the context of interest might be: It seems the only thing you’ve learned from your dogma.”

            To conclude, eric and those like him demonstrate clearly how dangerous religion / god-beliefs can be, as they replace critical thinking and logic while bolstering and trumpeting potentially planet-killing ignorance.

          • lindsncal

            You’re right. Thanks.

          • FreethinkingWorldGuy

            Sure, no problem!

            I also don’t let religion-subscribers get away with co-opting words like “faith” and “believe(r)”. From a phraseology / usage standpoint, they have largely co-opted those terms.

            But as a member of the AFAH community (atheists, freethinkers, agnostics and humanists) and speaking on behalf of that conglomerate group, we certainly do have faith; the difference is, we place it solely in worthy human beings, with none to spare on god-beliefs. And of course, we have beliefs too. Which leads me to…

            My kids have been taunted at school by Christians–once they have been “outed” as non- god-believers–as “Not believing in anything.” So I armed them with comebacks like “Of course I believe in things! For example, I believe you are a good person (or my friend, etc.). Is my belief on that misguided?” The prepping has paid off in a couple of cases, turning what might have been an awkward and/or humiliating moment into a humanity-related and relevant teaching opportunity.

          • lindsncal

            Smart, as usual from you.
            Is AFAH an actual visual joinable community or thing?

          • FreethinkingWorldGuy

            Thanks! I see a lot of smart stuff from you as well.

            If any of the letters that comprise AFAH represent you (or some mix, as is the case for me and others I know), then essentially you’re already a member of that community. In terms of fighting for equality–and as you’ve been fighting for in this thread, fundamental and basic reason–it’s analogous to LGBT(Q). So for example, anyone gay is already, by default, a member of that group.

            I use the acronym for a number of reasons, which includes simple economy of speech, but also, and more importantly, because the religious right(ous) likes to pigeonhole everyone not in their camp narrowly as “anti-God [and/or hating, angry] atheists.”

            In that spirit and more broadly, those represented by AFAH need to coalesce so that we acheive a truly representative voice and voting bloc–in particular somewhere on par with the power that evangelicals have enjoyed for years (…we see how the latter was immensely effective as a cofactor in terms of how DJT ended up as POTUS, and Christianist Mike Pence as VP).

    • lindsncal

      You can’t be serious. Guess you never noticed that no matter how much oil we have, prices don’t go down.
      Trump already wants to raise your gas tax 25 cents ..which would wipe out 60% of that temporary tax cut you got.



ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.


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