Ainissa Ramirez

Self-proclaimed science evangelist Ainissa Ramirez breaks down why leaves change colors


Ainissa Ramirez is a scientist, author, and self-proclaimed science evangelist.

She is the creator of a podcast series called 'Science Underground.'

She joins me now to discuss why leaves change colors during the autumn season.

It is the number-one question of every 5- or 6-year-old, I'm sure...

That's right.

...but it's also good to remind the adults that have to deal with those 5- or 6-year-olds.

What is it that's happening on a maybe chemical level to a leaf?

Well, there's a dance that's going on.

We have green, which is chlorophyll.

Chlorophyll is important for photosynthesis.

And chlorophyll starts to break down when the sun doesn't shine as much and when the temperature drops.

And when chlorophyll breaks down, what it does is it's like a curtain in front of a piece of art.

It drops, and behind it are other colors that are already present, and that's the yellow and the oranges.


So, it's an unmasking of colors that are already there.

And then it's also the creation, the production, of other colors -- the reds and the purples.

They happen at the end of the summer, and so they start to bubble up, and so that's when the reds and the purples come, as well.

So, why do the leaves start out green in spring?

It's just the chlorophyll that we're seeing?

Well, you need chlorophyll.

Chlorophyll -- I don't -- We don't have a national holiday for chlorophyll, but we actually should because it generates the energy so that the sun can, you know, transfer its light to a form of energy and help trees convert carbon dioxide to oxygen, so chlorophyll is a hardworking molecule.

Why is it sort of only in the kind of the ROY end of the spectrum and not the BIV that we see more colors changing?

Oh, good question.

Well, it ends up not all trees can change col-- Like, ginkgos can get to about yellow.

But then there's some really fantastic trees, like the sugar maple, which has this range of like a fire orange to reds.


So, it really has to do with the chemicals, the compounds, that are available in a tree.

So, you could conceivably have violet leaves if the chemicals inside the leaves were different?

That's right. That's right.

I mean, I'm seeing leaves that, on one side, you see the greens and yellows and then you see a little bit of the reddish on the other side, on one leaf.

So, does this happen in other seasonal plants, besides the trees that we're seeing -- I mean, basically, the chlorophyll unmasking process?

That's right.

It's generally happening to most trees.

And we're pretty lucky, because -- all right, I'm biased -- we're in the Northeast, but we're supposed to have the best palette of colors.

We don't have the most trees, but we have particularly the sugar maple, which has those reds, and a lot of other places don't have those fiery reds that the sugar maple has.

What makes an evergreen an evergreen?

That's a good question.

I would have to ask a dendrologist.

[ Both chuckle ]

Like, we have pine needles, right?

Yeah, pine needles.

They stay green. That's right.

And if it's not green, well, then you have a problem, 'cause that tree is dying.

So, yeah.

So, there's different classes of trees -- some that go through this process that get triggered by the amount of sun and by the temperature.

Temperature is very important.

You know, how does a tree know that the seasons are changing?


When the temperature dips at night, that's telling the tree, 'Okay, now we're entering another season.

Time to shut things down.

We're not doing the chlorophyll thing.

We're actually going to go into a kind of a sleep mode.'

Evergreens don't have that same kind of signal.

Sometimes you see some of those early, you know, kind of spring or early winter kind of frosts that kill off plants...


...and kind of change the clocks of the plants and the crops, and all of a sudden, you have massive die-offs...

That's right.

...where it shouldn't be.

That's right.

So, those anomalous weather events actually have pretty big economic consequences for farmers.

Absolutely, and, also, if we have a very warm summer and it goes into fall, October, and it's still warm, the leaves don't change color until much later, so there can also be a delay, and that has an economic impact, particularly in places like, you know, Vermont and New Hampshire, where they rely on the peepers, the leaf peepers, people coming out, spending their money to take pictures and the like.

Ainissa Ramirez, thanks so much.

Thank you.