Thanks to Brilliant for supporting  this episode of SciShow.

Go to Brilliant.org/SciShow to start their courses in math, science, and computer  science for all skill levels. [♪ INTRO]. Every spring, around 20% of the  population enters the season of sniffles.

Just how bad those few months  are depends on a lot of things, so usually, some years are worse than others. But lately, there just don’t  seem to be any “better” years. And it turns out we can thank climate  change for that, as the heat, higher CO2, and changing weather patterns all work  together to make allergy seasons extra awful.

Seasonal allergies or “hay fevers” happen  when your immune system glitches out and considers benign pollen  grains a dangerous intruder. The defense that it mounts  leads to common symptoms like a runny nose or itchy, red, watery eyes. And for some, it’s much worse.

Seasonal allergies can trigger asthma attacks or exacerbate other respiratory conditions  to the point of needing hospitalization. So bad allergy seasons are  really bad, and unfortunately, there are several ways that human-caused  climate change is making them worse. For starters, there’s the timing.

You see, when the weather gets warm, the flowers of wind-pollinated  plants start making pollen, a swarm of microscopic grains that  carry the plant’s genetic material. And I do mean swarm; each grain has a very  slim chance of landing where it needs to, so wind-pollinated plants always make lots  and lots of pollen to beat those odds. That’s why your nose is constantly blasted  with the stuff throughout allergy season.

And while there are a lot of theories  to explain what exactly triggers a plant to start producing pollen, ambient  temperature plays a key role. Pollen seasons start out when the  air and the ground get warmer. And as average temperatures  around the globe continue to rise, both pollen concentrations in the air and the duration of the  pollen season are increasing.

In some places warmer weather means  spring is, well, sprung earlier. For example, the 2018 pollen season in  the US started about 20 days earlier and lasted about eight days longer  than the pollen season in 1990. And, there was an average of 21% more pollen!

But even where that doesn’t happen,  we’re seeing worse allergy seasons. In some countries, the pollen  season now starts later, but scientists are still seeing  an increase in allergy symptoms. The reason for the late start  is that plants start flowering when they sense a temperature  change from cold to warm.

That used to mean “spring  is here, time for looove!” But as winters get warmer, spring  temperature rises aren’t as dramatic, so many species take a bit more  time to recognize the season change. This ultimately means species that  normally bloom at different times all start spitting out pollen at once,  which results in more allergens in the air. That’s why we’re seeing an 18% higher probability of developing hay fever symptoms  in places with later spring blooms, as compared to a 14% higher probability  in places where spring now starts earlier.

Though, it’s an increase either way! And it’s not just rising temperatures  throwing pollen seasons off kilter. It turns out that carbon dioxide itself, the main driver of climate  change, also lends a hand.

More CO2 boosts photosynthesis, the process plants use to get the energy  needed to build more of themselves. Regardless of temperature changes,  most species of plant mature faster and grow bigger and sturdier when  there’s more carbon dioxide in the air. And experiments have found that  even though plants in high CO2 don’t grow more flowers, the flowers they  do grow end up producing more pollen.

If atmospheric levels of carbon  dioxide keep rising as projected, research suggests that allergenic species may produce up to 200% more  pollen by the end of this century. And just in case that wasn’t bad enough,. CO2 can also make the pollen itself  pack more of an allergenic punch.

For example, at higher  concentrations of carbon dioxide, the notorious ragweeds pack more Amb a 1, one of their main allergens,  into their pollen grains. And overall, researchers estimate that  the concentration of Amb a 1 in pollen has risen by about 20% since pre-industrial  days, and will rise another 60% by 2050. And we’re still not done, because climate change is also favoring some allergy-inducing plants.

Overall, climate change is leading  to hotter, drier conditions. And it just so happens that  some allergy-inducing species, like hickory, oak, and slash pine,  do really well in hot, dry weather. So climate change will likely help them spread.

More of those trees means more  pollen, and more hay fever. You might think you’re safe because  you live far away from such forests. But you’re probably not, because  climate change may make it so that their pollen can still get to you.

Some research suggests that changing wind  patterns will expose people to pollen species from hundreds of kilometers away,  leading to new or unexpected allergies. Or, the winds may deliver pollen to areas  before the local pollen season starts. So basically everything about climate change, from rising temperatures to weather patterns,  seems to be working against your nose.

But though all this might sound pretty grim for people who experience seasonal  allergies, all hope is not lost. It’s more a reminder that the time to act is now, while we can still prevent the sneezy  future climate change has in store for us. Thanks for watching this episode of SciShow!

We hoped you enjoyed it,  and learned something new. And hey, if learning new  things is kind of your jam, we bet you’ll love today’s sponsor, Brilliant. They’ve really figured out  how to make STEM learning fun!

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