Humble Clumps of Moss Yield Sobering Climate Surprises

By Tom Yulsman | October 24, 2013 11:55 pm
The University of Colorado's Gifford Miller holds samples of moss collected on Baffin Island in the Canadian Arctic. (Photo: TKTKTK)

The University of Colorado’s Gifford Miller holds samples of moss collected on Baffin Island in the Canadian Arctic. (Photo: Matthew Kennedy, Earth
Vision Trust.)

It has been something of an article of faith among skeptics of humanity’s role in global warming: The rise in temperatures observed in recent decades can’t be definitively pinned on humans because nature — all by her lonesome — has produced temperatures during the past 11,000 years that were just as warm.

The logic: Since nature has produced a warmer Earth during this period without any intervention from us, we can’t rule out nature as the cause of the warming observed since the dawn of the industrial age.

But now, research involving clumps of moss that died at least 40,000 years ago has debunked this argument. (Whether it will go away is another subject entirely.)

The research, published online in Geophysical Research Letters on Oct. 21, shows that summer temperatures in the Canadian Arctic are higher today than they’ve been in at least 44,000 years, and are likely the warmest they’ve been in 120,000 years.

And there’s another sobering finding as well: Climate models may be significantly underestimating how much the Arctic will warm in coming decades.

In the interest of full disclosure, I should point out that the lead author of the new research, Gifford Miller, is a colleague of mine here at the University of Colorado. He’s a geoscientist. I’m a journalism professor and science journalist. Miller told me about his results last spring, and I’ve been waiting for his study to be published in a peer-reviewed journal before writing about them.

So here’s the story of how long-dead clumps of moss helped Miller and his colleagues come up with their new findings…

Southern Baffin Island and the Penny Ice Cap is visible in this image captured by NASA's Aqua satellite on August 11, 2013. (Image: NASA)

Southern Baffin Island and the Penny Ice Cap are visible in this image captured by NASA’s Aqua satellite on August 11, 2013. (Image: NASA)

The story actually starts in the 1980s when Miller landed in a helicopter near a small ice cap in the highlands of Canada’s Baffin Island in the Arctic. These bodies of ice are unlike glaciers in that they are small and do not flow like rivers. As a result, they do not crush and grind everything beneath them, including vegetation.

Miller recalls that he collected some samples of plants and then flew off.

Years later, he found himself teaching freshmen in a large lecture class. He decided that he wanted to update his talk on climate change in the Arctic, which is proceeding faster than elsewhere, thanks to a phenomenon known as “Arctic amplification.” So he decided to look for satellite images of the same ice cap he had landed next to all those many years before and use them to illustrate the phenomenon.

But there was a problem: He couldn’t find the ice cap in the pictures at all. Thanks to warming, it had simply vanished.

“There’s something about extinction that’s more impressive than simple recession,” he told me today, speaking of the total disappearance of the ice.

Ice caps are actually disappearing all across Baffin Island. In the past 20 years “the warming signal from that region has been just stunning,” Miller says (quoted in a press release from the Institute of Arctic and Alpine Research, where he is a fellow.). “All of Baffin Island is melting, and we expect all of the ice caps to eventually disappear, even if there is no additional warming.”

The vanishing of the ice cap he noticed in satellite imagery did have one positive effect — it prompted a fascinating research idea: Go to Baffin Island, collect dead vegetation that has been exposed by receding ice caps, and use radiocarbon dating to determine when those plants took their last breath, figuratively speaking, before being covered up by the ice and dying.

Here’s the logic: Those plants were last alive when they were exposed to the air and sun — in other words, when the ice caps were smaller, and therefore the climate was warmer. So by dating when the plants died, it would be possible to say when the climate became cold enough for the ice cap to expand and cover them up.

Giff Miller's camp on Baffin Island in August of 2013. (Photo: Matthew Kennedy, Earth Vision Trust.)

Giff Miller’s camp on Baffin Island in August of 2013. (Photo: Matthew Kennedy, Earth
Vision Trust.)

Over the course of three summer field seasons, the team collected 365 samples from the edges of about 110 different ice caps in a 1,000 kilometer transect along the highlands of Baffin Island. Of those, the researchers were able to obtain 145 carbon-14 dates, most commonly on rooted clumps of a moss.

The radiocarbon dating revealed that the vast majority of the mosses were killed by expansion of ice following the end of a warm period about 5,000 years ago. They were only recently uncovered as the ice retreated under the influence of warming temperatures. This means temperatures now are warmer than they’ve been for at least that period of time.

That was interesting enough. But then came a big surprise.

The researchers discovered four small summit ice caps where retreating ice had recently uncovered clumps of moss that dated to at least 44,000 years ago. This moss must have been ice covered in all of the intervening years — until becoming exposed in today’s warm climate.

And that’s not all. It turns out that in all likelihood these moss clumps are even older than that. Much older, in fact.

Here’s why: Forty-four thousand years is almost at the limit for radiocarbon dating. Past about that point it simply doesn’t work very well. So, 44,000 years ago has to be the minimum estimate for when these moss clumps were last alive and exposed to the atmosphere.

And it even gets curiouser. Forty-four thousand years ago, the Northern Hemisphere was in the grips of the Ice Age, a profound cold period that began 120,000 years ago. In other words, these moss clumps have probably been locked under ice for 120,000 years, only becoming exposed when today’s warming temperatures caused the ice caps to shrink enough to reveal them.

These findings show that the recent warmth experienced in the Arctic is “well outside range of any natural variability and can only be explained by increases in greenhouse gases,” Miller says. “Natural variability can’t be the main contributor.”

The likely culprit is the increasing concentrations of heat-trapping greenhouse gases in the atmosphere caused by fossil-fuel burning and other human activities.

Giff Miller hikes the highlands of Baffin Island in August of 2013. (Photo: Matthew Kennedy, Earth Vision Trust.)

Giff Miller hikes the highlands of Baffin Island in August of 2013. (Photo: Matthew Kennedy, Earth
Vision Trust.)

And there’s even more to the story.

The mosses also helped the research team to reconstruct the evolution of the snowline around Baffin Island ice caps. From this they were able, in turn, to determine how temperatures have changed over the course of many millennia

It has long been known that prior to the current warming, the Arctic has been cooling for most of the past 5,000 years. The cause: shifts in the amount of solar energy reaching Earth brought about by natural changes in our planet’s orientation relative to the sun. Scientists have used computer models to determine just how much cooling this phenomenon should have caused. But the data from Miller’s research show that the actual cooling was about twice the response predicted by climate models.

So here’s the rub: Those same models are used to predict the future course of climate change. Based on the new results, Miller says the models probably are predicting slower and less intense warming in the Arctic than may be in store.

Why is that? The same climatic feedback mechanisms that would tend to enhance cooling in the Arctic would also operate in reverse and enhance warming.

If you’ve made it all the way through to this point, you may be wondering whether clumps of moss on a single island in the Canadian Arctic are reflective of climate shifts throughout the Arctic. Miller has been wondering about that too, so he and his team have been collecting plants from sites in Iceland, Greenland and Svalbard. Those results haven’t been published yet, so stay tuned.

But my educated guess is that they are going to show a similar picture.

  • Paulie777

    You’re third to last paragraph says that based on the results Miller is predicting slower and less intense warming in the Arctic than may be in store. This is a good thing, no?

    • Susan Fox-Pieratti

      Based on the NEW results, Miller says the MODELS probably are predicting slower and less intense warming in the Arctic THAN MAY BE IN STORE…..I had to read it twice… It is not a good thing. They’re saying that the original models are wrong.

  • Paulie777

    Oh the models are predicting less, not Miller. I was looking for some type of conclusion, I read it wrong. It should have read “based on the results Miller believes there will be faster and more intense warming than the models predict. This focuses on Millers work and not the what the models say right near the most important part of the piece.

  • Jim Acker

    Hey Tom, you should mention that the MODIS instrument on Aqua was the one that acquired the image. Some people think that there’s only one instrument on these satellites!

  • Kyle R Johnson

    When Earths atmosphere transformed because of plant activity, NOBODY said a word. Probably because without that plant activity there would be no higher life to say words. Thank you plants for screwing up the old atmosphere to make room for us humans. Who will be thanking us for being humans and transforming the atmosphere?

    Are humans not natural creatures of Earth? Why should we feel guilty about our activity. Decaying plant matter and natural plant metabolism didn’t give rise to guilt. It gave rise to OXYGEN and NITROGEN.

    I think the Earth speaks to all of us similar to the way we speak to our bodies NATURAL biological systems.

    I also think there is plenty of room for a new species to crawl up out of this goop we’re all swimming in and…

    • Michele Erica



    Thanks for the information. I am not a scientist but this certainly needs to be studied more. I wonder what impact Volcanoes have and do we really know what triggers them to spew and will that spark another ice age? This information will be very important to understand.

  • lrw

    Too much glee in the author’s tone to support his heady conclusions. I have no doubt that the moss has been dead as long as asserted.
    But, there is nothing here that settles whether or how many times that DEAD moss has been RECOVERED by ice. Just because the latest melt revealed it — logically doesn’t mean it wasn’t exposed before in geologically brief periods like between the MWarmPeriod and the The Little Ice Age for example. OR that it isn’t MIXED with lower concentrations of Moss from more recent warm periods.

    • Brian Schmidt

      When uncovered, the dead moss would decay from exposure to rain, light, consumption by microorganisms, and breakdown by other plants and moss. Granted in that frigid environment it might take a few months or years, but that’s quick on a geological scale. If the climate had warmed up more than briefly in the previous 44k years, the moss would not now exist.

      • lrw

        There are dead moss deposits all over the globe that are THOUSANDS of years old. And they are in areas of IMMENSELY more active bio activity than an arid tundra. Perhaps you’ve heard of peat? A prized ROOFING and insulation material of the ancients?
        Those samples could have been “uncovered” briefly (100 yrs) 10 times in the past 10,000 yrs. After all, those haven’t YET been uncovered long — have they?

        • Brian Schmidt

          Peat is partially decayed vegetation, occurring underwater in low oxygen conditions, usually in high acidity. None of that applies to this situation of nondecayed moss exposed to air, oxygen, and at normal pH. Go to the U Colorado website to see how pristine the moss looks.

          • lrw

            Moss decomposes very slowly in that enviro.. See for instance.
            “Because they produce biomass that, in general, decomposes slowly, mosses over time also contribute to the formation of microtopography maintenance of seasonal ice and permafrost, and the formation of ombrotrophic conditions”
            Or the dated samples of peat picked up on the Arctic Tundra in —-
            “Peat formation in polar regions is much slower than at lower latitudes, since tundra plant growth is limited to a short and cold arctic summer. However melt and rainwater in the soil above the omnipresent permafrost layer at the depth of
            10 –100 cm (Rønning 1996) helps to preserve dead
            plant material. Once dead plant material has left the active layer and forms part of the permafrost,
            microbial and chemical decay is very slow or absent, and preservation of organic plant matter including pollen and spores is optimal.”

            These samples dated back 1000s of years, and were NOT in a lake.
            In a very short time, I think the glee and credibility of this study will both be gone.

          • Brian Schmidt

            Your second link describes peat formed below the plant surface, no light exposure, low oxygen, and either waterlogged or frozen in permafrost (also, it’s peat, which these samples weren’t). What I could read from your first link doesn’t seem all that relevant to whether a moss patch could persists as you’ve suggested.

    • Bob Martin

      No matter how solid the evidence “some will say” the earth is flat and it’s all a conspiracy to take away the poor oil company’s hard earned profits.

  • Jane Morrisant

    Here’s a recent tree ring study in Finland showing that the current warm phase is still COOLER than the last two warm phases, the Medieval Warm Period and the Late Roman Warm Period:

    Amazing what that planetary emergency of skyrocketing temperatures looks like. When the study is conducted outside the gang of communist political operatives, that has seized control of the climatology establishment, and just about crushed all dissent within that small academic field.

    It was much warmer than today during the Mid-Holocene Climatic Optimum (or Maximum) from about 8000-3000BC. Denmark had a Mediterranean climate. That was the actual warmest point since the Eemian Interglacial 120,000 years ago. But Baffin Island was still thickly covered in residual glaciers from the last ice age, which have been melting since.

    As the authors of this current study well know — and are just forgetting to mention, so they can produce another sensationalistic propaganda headline that sounds like the Earth is burning up.

    • Karl A. Anderson

      Heh. Ms. Morrisant is right up front with the foundation of her denialism:

      “When the study is conducted outside the gang of communist political operatives, that has seized control of the climatology establishment, and just about crushed all dissent within that small academic field.”

      What’s the first claim a science-denier makes? Conspiracy!
      “Almost every denialist argument will eventually devolve into a conspiracy.” (

      Ms. Morrisant, having pronounced the “small academic field” of climatology to be under the control of communists, then cites a single study by members of that very academic field, which she thinks contradicts “the climatology establishment”.

      She has now demonstrated the second-favorite tactic of the denier: Cherry-picking! “Denialists tend to cite single papers supporting their idea (often you have to squint to see how it supports their argument).” (

      One has to wonder why Ms. Morrisant trusts the authors of her cherry-picked study (which doesn’t say what she thinks it does), when she’s declared her hatred of the “climatology establishment.” Could it be she just can’t stand the idea that AGW might be real?

    • wbramh

      Jane, Jane, Jane,
      This is the year 2013.
      You’re supposed to be frightened of Muslims now, not commies.

      KGB Putin has become the hero of the deniers and those Red Chinese are busy surpassing the U.S. as dutiful polluters of our plentiful Earth – just as the Bible instructs us.
      In other words, the Pinkos are on YOUR side so let up on the negative Ommie-Cay Uff-Stay – Okay-yay?

      In the meantime, thousands of al Qaida’s top scientists are attempting to destroy the World before Jesus returns to destroy the World.
      We can’t let that happen! Jesus needs a landing strip or the whole Biblical end-of-days meme goes North with the temperature.

      Get your talking points updated and all will be fine.

    • Brian Schmidt

      Well Ms. Morrisant, if you accept tree ring methodology then we may have something to talk about, but you’re not going to like the broader conclusion that goes beyond this one study of Lapland.

  • lrw

    So Miller says —- “”In the past 20 years “the warming signal from that region has been just stunning,” Miller says””
    REALLY? Do we get the picture of RAPIDLY RISING temps associated with that stunning assertion?

    Take a look at the Baffin Weather Stn temp record above and tell me that those ice caps weren’t doomed WELL before CO2 levels became significant.
    The choice of rhetoric is this whole press release pkg is what’s “stunning”..

  • jh

    Mr. Geo:

    I’ve noticed that science journalists are inclined to see new research results as definitive.

    From my 25 yrs as a geologist, I’ve seen “definitive” results come and go. It takes 5-10 yrs to prove up new results. In most cases, significant contrary evidence emerges during that process. The result in the long run is that several lines of evidence disagree and its left to the judgement of the geologist to weight the different lines of evidence: that is, the evidence is rarely definitive.



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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