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(bright music)
(birds chirp)

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- [Narrator] Stretching
across the top of our planet

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like a verdant, green crown,

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the boreal forest is Earth's
largest forested biome.

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Home to moose, wolf, caribou, bear,

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and countless other species,

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this vast wilderness of
spruce, fir, and pine

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holds more than a third
of the world's forests

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and stores massive amounts of carbon,

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helping regulate our global climate.

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But this forested frontier is changing,

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and, for years, scientists
could only theorize about how.

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The Earth's system is complex and dynamic,

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with feedback mechanisms

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that can drive positive
and negative outcomes.

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- For decades, there have been

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ecological and climatological models

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that have theoretically predicted

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that the boreal forest,
given climate change,

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should be moving north.

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- [Narrator] Previous
studies provided hints:

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regional evidence, indirect measurements,

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but the boreal forest
changes slowly, very slowly.

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To truly see what's happening,

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you'd need to watch the entire forest

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continuously for decades.

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So how could researchers
possibly test this hypothesis

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at such a massive scale?

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Enter Landsat:

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NASA's longest running
earth observation program.

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For the first time,

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scientists could analyze
the entire boreal forest

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using the complete Landsat archive.

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- This study is the first and only study

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to comprehensively study
the entire boreal forest

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from 1984 to 2020,

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using 224,000 Landsat images,

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mapping the tree cover in every
pixel, 30-meter resolution,

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and then testing whether or not

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the boreal forest is moving north.

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- [Narrator] The research team,
led by NASA and terraPulse,

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calibrated Landsat satellite data

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using NASA's airborne field
campaign lidar measurements

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and commercial images

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to create the most accurate map

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of boreal tree cover ever produced.

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They then tracked changes
in every 30-meter pixel,

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an area about the size
of a baseball diamond,

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across 36 years,

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in the entire circumboreal region.

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The scope is staggering,

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analyzing the complete
northern forest belt

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spanning Alaska, Canada,
Scandinavia, and Russia.

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- The study's groundbreaking
just in its sheer scope.

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The longest record,
the highest resolution.

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Data were calibrated using lidar.

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I mean, just every resource
was thrown at this study

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to get the final, definitive answer.

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- [Narrator] And the answer is clear:

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the boreal forest is shifting north.

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Between 1985 and 2020,

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the forest's median
latitude moved northward

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by 0.43 degrees, roughly 60 kilometers.

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The forest also expanded

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by 844,000 square
kilometers, a 12% increase.

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And it's getting denser,

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with tree cover increasing
across most latitudes.

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- What we found is that the
forest is getting denser

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across most latitudes.

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At the very southern edge
of the boreal forest,

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there are a couple slices,
latitudinal slices,

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where the the net change of
the forest is being lost.

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But the pattern of those losses

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is pretty consistent over time,

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and those changes within
latitude across time

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aren't really changing
as much as the growth.

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- [Narrator] The boreal
forest's northward shift

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affects everything,

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from managing fuel load fire risk

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to industrial operations
of timber, oil, and mining,

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extracting resources across
North America and Eurasia.

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It changes wildlife habitats

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and the forest's ability to store carbon.

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The expanding forest is
also getting younger,

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with fast-growing trees

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that could sequester additional carbon

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if allowed to mature,

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a potential positive outcome
of warming and climate benefit.

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Yet other factors could
drive negative outcomes,

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which requires additional studies.

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- The boreal forest is poised
for a major transition.

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Permafrost is thawing.

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The forest composition is changing.

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All of these things can lead

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to an abrupt shift in the ecosystem

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from one type to a
completely different type.

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With shorter term or less calibrated data,

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we can see abrupt changes.

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But with the long-term, highly
calibrated Landsat data,

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we can see the slow changes.

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It makes it sort of a
canary in the coal mine.

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It's a slow canary,

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but if we have the long-term,

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high-resolution, highly calibrated data,

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which Landsat gives us,

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then we can listen to its song.

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- [Narrator] This research represents

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the most comprehensive analysis

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of boreal forest change ever conducted,

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made possible by decades
of Landsat observations

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and NASA's commitment to
understanding our changing planet.

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(light upbeat music)