It's autumn here in the nation's capital, and that means that in a normal year, trees would be bursting with color, the air would turn crisp, and harvest apples and seasonal apple products would fill store shelves.

Except that right now, apple growers in Virginia's Shenandoah Valley are struggling to grow apples, and climate change is to blame.

The really bad news isn't that Virginia apple harvests are failing, that's just a signpost for some of the most dire climate change scenarios that we're heading for.

Because if apple trees are starting to fail and die as our planet warms and climate changes, trees of every type will start to fail and die too.

NASA's Goddard Institute for Space Studies recently reported that September 2016 "was the warmest September in 136 years of modern record-keeping."

There's no doubt that the planet's climate is changing, and it's threatening countless species of plants and trees that won't be able to adapt to such rapid changes because of their specialized evolution and inability to migrate.

Trees can't pick up roots and move, and different species of trees are differently adapted to particular types of soils, growing seasons, water availability and even altitudes, so trees are especially vulnerable to the shifting climate zones of a warming planet.

And that will have profound impacts on the health of our planet and future generations.

Most people understand that trees are the planets lungs, they literally breathe in carbon dioxide through leaves, and then they exhale oxygen as their waste, which you and I are breathing right now.

When trees "inhale" carbon dioxide though, they don't JUST "exhale" oxygen, they also trap carbon in their wood, and the bigger they grow, the more carbon they hold.

Beyond that, the root structures of trees are necessary for healthy soils, and healthy soils hold in significant amounts of carbon trapped from the atmosphere.

When trees die though, those processes are reversed: trees stop capturing carbon, and start emitting carbon as their wood rots and the tree decays.

So as trees die because of our warming planet's shifting climates, the warming will actually accelerate, because the dying trees will release once-stored-carbon back into the atmosphere.

But that's not all that trees do for us; as I wrote in my book: "The Last Hours of Ancient Sunlight," it's barely even the beginning.

Trees are also essential to our planet's water cycle, and water issues are only going to get worse as climate change threatens forest habitats across the planet.

We're already facing a number of drinking water crises around the world, in part because of how humans have mismanaged our water resources, but also in large part because our reckless management of forest resources has fundamentally disrupted the water cycle across many parts of the world.

In a healthy forest ecosystem, rain falls from the sky, and soaks into the ground.

As the water seeps into the ground, it generally absorbs high concentrations of dissolved minerals, especially salts.

Then, the roots of a tree draws moisture from just above the salty water, pumping the moisture into the atmosphere through the tree's leaves, and absorbing the minerals into the tree's wood.

When it rains again, the moisture from the soil is replaced, and the cycle continues, keeping the soils and the trees healthy.

When trees die though, the saltier water underground is allowed to creep upward, infiltrating closer and closer to the surface, until it damages the surviving trees' immune systems and makes them vulnerable to parasitic infections.

Then, if no trees are able to grow back, the salty water will infiltrate even further towards the surface, killing crops and ultimately leading to desertification.

It's a scenario we've seen play out across the world: from California to the Mediterranean and from Senegal to China, deforestation has destroyed soils, polluted water, and left huge swaths of desert wasteland.

On average, it takes about 400 years for a forest to create a foot of topsoil that is capable of sustaining crops, but without healthy forests, there is almost no topsoil created at all.

Without healthy topsoil, humans can't grow agriculture. And without growing agriculture, humans will face global starvation.

Failing apple orchards aren't the end of the world, but they are a signpost for the potential disasters to come if we don't take bold and immediate action.

We need to start respecting how necessary forests are for the health of our planet (and our species!), and that means putting an end to slash-and-burn farming and severely limiting the practice of clearcutting forests.

Instead, we need to start intelligently re-planting forests to help suck CO2 out of the atmosphere, to help re-balance the water cycle, and to produce healthy top soils that will sustain future generations.

We also need to tackle the threat of climate change at its core, by putting a price on carbon and by investing massively in renewable technologies and technologies to capture planet-warming carbon from the atmosphere - and then we may be able to move towards a world that works for all.