How are your allergies affected by climate change?

One effect of climate change is that spring comes sooner and summer stays longer.  A longer summer makes ragweed and other plants pump out more pollen — making us miserable.

An analysis of pollen data for the past few decades shows that the pollen producing season of ragweed has increased by up to 27 days as you go north from Oklahoma up into Canada. This is undeniable evidence of a warming world.

Unfortunately, for folks like me, with a terrible allergy to ragweed, this is bad news.  Fortunately, I don’t have asthma, but for those who do, it’s even worse. Asthma can be triggered by allergies to pollen, and it can be life-threatening.

Also, if that weren’t bad enough, recent evidence shows that in a warming world, the combo of increasing levels of ozone and pollen are a double whammy for folks with asthma and other chronic lung diseases.

The Devil’s own… Ragweed!


Let’s dig into some details about ragweed and climate…

A nice bit of work was done by Dr. Lewis Ziska, PhD (in plant physiology) from the US Department of Agriculture and his team.  This kind of work is what we research types call “low hanging fruit,” meaning that the data speaks for itself — no fancy footwork is needed to explain the findings.

These scientists gathered all the ragweed pollen data that they could get and plotted it out by time and latitude (equator to pole, or “ladder-tude” as I learned to remember it back in elementary school science class).

What they found stood out loud and clear — the further north you go, the longer the ragweed season has become since 1995.  I bet if they had data going further back, the changes would be even more striking.

You can get Dr Ziska’s article for free…  Ziska, L, et al (2011) Recent warming by latitude associated with increased length of ragweed pollen season in central North America,  PNAS, vol. 108, no. 10, p. 4248–4251.

The increase in the ragweed season is caused by increased number of frost-free days (days above freezing) due to a warming climate — as you can see in these next few graphs.  Fewer cold days means that ragweed and other pollen producing plants start making pollen sooner… and keep on making it longer.


Increase in Frost-free days over time for the whole U.S. ~ From:


From the US Global Change Program…

“The bars on the graph show the difference between the number of frost-free days in each year and the average number of frost-free days from 1979 to 2010. Global daily freeze-thaw data are provided by the National Aeronautics and Space Administration (NASA) Freeze-Thaw Earth Systems Data Record, which represents one of the longest continuous global records from satellite-based observations.”


The next graph shows the same info broken out by region.  The increase in frost-free days in the western states is pretty incredible.  This change is probably why there is a huge pine beetle infestation that is killing off millions of acres of forest from New Mexico to British Columbia, but that’s a post for another day.

Observed change in the frost-free season length by region, from 1958 to 2012 — From…


This next figure from the Ziska study combines both bits of data in one graph.  Change in frost-free days on the vertical axis, and change in length of ragweed pollen season on the bottom axis.  If both of these things happen the further north you go, then you would expect the data points (various symbols on the graph) to line up from lower left to upper right –or– from lower to higher latitudes… and of course this is exactly what we see.

Change in the length (days) of ragweed pollen season from 1995 to 2009 as a function of frost-free days, and delays in the time of first frost during the fall, for 10 central North American locations (eight in the United States and two in Canada) as a function of latitude. From Ziska, et al (2011).


Here’s a nice graph put together by the US Global Change Program that summarizes the same info in a more understandable way.  They say…

“Ragweed pollen season length has increased in central North America between 1995 and 2011 by as much as 11 to 27 days in parts of the U.S. and Canada in response to rising temperatures. Increases in the length of this allergenic pollen season are correlated with increases in the number of days before the first frost. As shown in the figure, the largest increases have been observed in northern cities.”

Ragweed pollen season length has increased in central North America between 1995 and 2011.


Of course, ragweed isn’t the only pollen that has increased; it’s just one of the most studied here in the US.  And besides, ragweed causes more allergies than all other plants combined.

Other pollen counts that are increasing around the world, include birch pollen in Northern Europe, cedar pollen in Japan, and pellitory and other weeds in the Mediterranean, to name just a few I saw while skimming through the scientific literature.

Another point for consideration is that increasing CO2 causes ragweed to make even MORE pollen.  This was studied by our pal, Dr. Ziska and his crew in the lab.  That work is summed up in the following figure.

Pollen production from ragweed grown in chambers.

Here’s what they say about this figure…

“Pollen production from ragweed grown in chambers at the carbon dioxide concentration of a century ago was about 5 grams per plant; at today’s approximate carbon dioxide level, it was about 10 grams, and at a level projected to occur about 2075 under the higher emissions scenario (A2), it was about 20 grams. (Source: Ziska LH, Caulfield FA. Rising carbon dioxide and pollen production of common ragweed, a known allergy-inducing species: implications for public health. Aust J Plant Physiol. 2000;27:893–898.)”

Some folks might say that longer growing seasons and more CO2 for plants must be a good thing.  However, nothing could be further from the truth.  A warming planet also leads to drought in one area and floods in another, neither of which is good for growing crops.  AND, it’s not always the case that more CO2 and more heat are good for all plants.  Take corn for instance.  Corn pollen is sensitive to heat, which destroys it.  So corn crops will be adversely affected in a warming world.


What are the medical implications of increasing pollen?

There’s lots of work that’s been done on linking pollen to increased visits to the doctor’s office or emergency department (ED).  If more pollen is produced because of climate change then this kind of work is really important so we can know what the impacts are on people with allergies, asthma, and lung disease.

After sorting through a few medical papers I find that ragweed is not necessarily associated with increased asthma attacks, BUT high levels of tree and grass pollen ARE associated.  Part of the problem with teasing out the effect of ragweed is that the peak of ragweed pollen production is late summer/early fall, which coincides with the seasonal onset of the common cold, which also triggers asthma.

However, ragweed is still a major cause of allergic suffering, and if ragweed pollen is increasing, then so is the pollen of other plants.  Also, it depends on where your study is located.  In the chart below from a great study by Dr Lyndsey Darrow and company at the Emory School of Public Health in Atlanta, pollen data and ED visits are compared.

The first figure shows the seasonal peaks for different pollens, while the second shows the risk of ED visits for asthma versus the pollen concentration in the air.  The data shows is that over 11 years (1993 to 2004), high levels of oak tree pollen (Quercus) and grasses (Poaceae) are directly associated with increased visits to the ED for asthma.  Children 5 to 17 years old were especially susceptible to oak tree pollen, while adults (18 to 39 years old) had more asthma attacks due to grass pollen.



In the next figure, anything that is above the dark black line shows a positive link between ED visits for asthma and high pollen levels.  The data points (black dots) are surrounded by error bars (called confidence intervals in statistics).  If the black dots fall below the dark black line, then there is NO link.  If the error bars touch the black line, then you can’t say either way.  HOWEVER, if the black dot AND the error bars are above the black line, then there is a definite link between pollen levels and ED visits for asthma.  As you can see, there is a strong link between high Oak and grass pollen levels and ED visits (red arrows).



Of course, this data is mostly relevant for Atlanta, but it does a great job of showing that ED visits for asthma are linked to high pollen levels in general.  This work has important implications for other regions of the country and the world.

You can get Dr Darrow’s article for free…  Darrow, L, et al (2012). Ambient pollen concentrations and emergency department visits for asthma and wheeze, J Allergy Clin Immunol, 130(3):630-638


What should you do if you have allergies, asthma or lung disease?

Well that all sucks pretty bad, so what can we do about it?  Beyond the obvious long-term solution of reducing our own production of CO2, divesting your retirement and other investments from fossil fuels, and supporting policies and politicians that want to help us transition away from dirty fossil fuels; there are several measures we can take to protect ourselves in our personal lives.

If you have asthma or another lung disease make sure your asthma is well-controlled.  To a doctor, there are certain criteria for “well-controlled”.  So be sure that you go see your doc and get tuned up if you have any concerns.  The Mayo Clinic has a nice summary of what to do if you have allergic asthma, and if you want a bit more detail, check out the American Academy of Allergy, Asthma, and Immunology.

Here are a few things that you can do if you have bad allergies (with or without asthma).  These items are based on my life-long battle with bad seasonal allergies.

  • First and foremost, get your allergies treated.  There are excellent medications available these days.
    • If your allergies aren’t that bad, then there are lots of over the counter medications.  Ask your local pharmacist.
    • If your allergies are a little worse, see your regular doctor to get some stronger prescription meds
    • If your allergies are bad, get your doctor to refer you to a specialist for allergy testing (I had allergy shots as a kid.  It helped, but they do wear off over time or if you move somewhere new)
  • Keep the windows closed at the height of allergy season and use your AC (powered by renewable energy of course! )
  • Put high-efficiency filters in your A/C   (link at bottom of page)
  • I also use a stand alone air filtration unit with a HEPA filter (catches really small bits in the air, like pollen)  (link at the bottom of the page)
    • HEPA stands for High Efficiency Particulate Arrestor
  • Keep your carpets clean.  A vacuum with a HEPA filter is helpful, but often expensive
    • better yet, move to a place with hardwood or tile floors, which are easier to clean (or install them yourself if possible)
  • Make sure all the little gaps around your doors and windows are appropriately sealed
  • Know when the particular pollen level that bothers you is at its highest
    • stay indoors on bad pollen days or take your meds
    • You can check pollen levels in your area –> here.



Well there you have it, a warming world due to climate change is not a pleasant place for us folks with allergies, asthma or lung disease.  Let’s summarize what we’ve gone over in this post…

  • There are fewer frost-free days due to climate change and longer growing seasons
  • Pollen producing plants like ragweed are pumping out more pollen
  • Plants we like, such as corn, may not do well in a warming world
  • People with allergies and lung disease will be even more miserable
  • This is happening here and now
  • There are plenty of great prevention and treatment options available

Thank you for reading.  If you have a question or comment, please tweet me.  If you enjoyed this post, please consider subscribing.

Next time, a post about the recent flooding in Texas, and a discussion of the link to climate change, if any.  Until then… Cheers!

PS  Check out this video for an interview with Dr. Ziska about climate change, weeds, and the future of agriculture.

Here’s the air filter I use, by TheraPure.  I got it at CostCo few years ago, where they sold it for many years.  I think they have recently switched to a different model, but I like the original.  The HEPA filter is permanent, so no costly replacements.  Here’s an affiliate link to Amazon for the Envion Therapure TPP440 Permanent HEPA Type Air Purifier.

TheraPure air filter

And here are the A/C filters I use from Filtrete.  Makes a definite difference, at least to me.

Filtrete Air Filters

I just got this vacuum, the Hoover Windtunnel Air Bagless Upright, UH70400 w/ HEPA filter(!).  It works great.  I especially like that it stops by itself when the brush gets tangled up in something, like the fringe on the end of my Persian rugs.

HEPA vacuum!