Study: plants do better during drought thanks to increased CO2 levels


Climate change has less impact on drought than previously expected
Plants retain more moisture in high carbon dioxide conditions, keeping water on land

Irvine, Calif., Aug. 29, 2016 – As a multiyear drought grinds on in the Southwestern United States, many wonder about the impact of global climate change on more frequent and longer dry spells. As humans emit more carbon dioxide into the atmosphere, how will water supply for people, farms, and forests be affected?

A new study from the University of California, Irvine and the University of Washington shows that water conserved by plants under high CO2 conditions compensates for much of the effect of warmer temperatures, retaining more water on land than predicted in commonly used drought assessments.

According to the study published this week in the Proceedings of the National Academy of Sciences, the implications of plants needing less water with more CO2 in the environment changes assumptions of climate change impacts on agriculture, water resources, wildfire risk, and plant growth.

The study compares current drought indices with ones that take into account changes in plant water use. Reduced precipitation will increase droughts across southern North America, southern Europe and northeastern South America. But the results show that in Central Africa and temperate Asia — including China, the Middle East, East Asia and most of Russia — water conservation by plants will largely counteract the parching due to climate change.

“This study confirms that drought will intensify in many regions in the future,” said coauthor James Randerson, UCI professor of Earth system science. “It also shows that plant water needs will have an important influence on water availability, and this part of the equation has been neglected in many drought and hydrology studies.”

Recent studies have estimated that more than 70 percent of our planet will experience more drought as carbon dioxide levels quadruple from pre-industrial levels over about the next 100 years. But when researchers account for changes in plants’ water needs, this falls to 37 percent, with bigger differences concentrated in certain regions.

The reason is that when Earth’s atmosphere holds more carbon dioxide, plants actually benefit from having more of the molecules they need to build their carbon-rich bodies. Plants take in carbon dioxide through tiny openings called stomata that cover their leaves. But as they draw in carbon dioxide, moisture escapes. When carbon dioxide is more plentiful, the stomata don’t need to be open for as long, and so the plants lose less water. The plants thus draw less water from the soil through their roots.

Global climate models already account for these changes in plant growth. But many estimates of future drought use today’s standard indices, like the Palmer Drought Severity Index, which only consider atmospheric variables such as future temperature, humidity and precipitation.

“New satellite observations and improvements in our understanding hydrological cycle have led to significant advances in our ability to model changes in soil moisture,” said Randerson. “Unfortunately, using proxy estimates of drought stress can give us misleading results because they ignore well-established principles from plant physiology.”

Planners will need accurate long-term drought predictions to design future water supplies, anticipate ecosystem stresses, project wildfire risks and decide where to locate agricultural fields.

“In some sense there’s an easy solution to this problem, which is we just have to create new metrics that take into account what the plants are doing,” said lead author Abigail Swann, a University of Washington assistant professor of atmospheric sciences. “We already have the information to do that; we just have to be more careful about ensuring that we’re considering the role of the plants.”

Is this good news for climate change? Although the drying may be less extreme than in some current estimates, droughts will certainly increase, researchers said, and other aspects of climate change could have severe effects on vegetation.

“There’s a lot we don’t know, especially about hot droughts,” Swann said. The same drought at a higher temperature might have more severe impacts, she noted, or might make plants more stressed and susceptible to pests.

“Even if droughts are not extremely more prevalent or frequent, they may be more deadly when they do happen,” she said.


Other co-authors are Forrest Hoffman at Oak Ridge National Laboratory and Charles Koven at Lawrence Berkeley National Laboratory. The research was funded by the National Science Foundation and the U.S. Department of Energy Office of Science.


65 thoughts on “Study: plants do better during drought thanks to increased CO2 levels

    • Yup. It is amazing how far ahead science deniers are from the scientifically literate.

      Deniers were first to understand
      – the pause
      – global greening
      – that Antarctic sea ice was increasing
      – that plants would be drought resistant

      Any others, there has to be more.

      They still haven’t figured out…
      – that the models are bad
      – that nuclear is a viable solution
      – that not all subsidies are the same
      – that Exxon knew as much as the IPCC
      – that the debate is about rate not basic physics
      – that extreme weather remains unchanged
      – that polar bears are fine

      Eventually they will catch up.

    • We used to understand this – then science went backwards for several decades,


      Circa the 1960’s, comedian Shelley Berman said:

      “No matter how mean, or cruel, or sinful you have been, every time you breathe out, you make a little flower happy.”


    • Just when you thought that “It’s worse than we thought”, we find it’s worse than we thought we thought!

  1. …. carbon dioxide levels quadruple from pre-industrial levels over the next hundred years.”
    1200+ ppm in 2100 AD?
    I don’t recall seeing that one anywhere.

    • I thought someone in a previous thread calculated that there wasn’t enough fossil fuel (i.e., coal, gas and oil) left on the planet to double the CO2 level after the current doubling.

      • The calculation requires making a lot of assumptions about use rates, economics, population growth, sources and sinks, etc, but some analysts see 600 ppm as the limit.

        Which is too bad for all those plants which would prefer 800 to 1200 ppm.

      • Ah, yes, but the real source of the increase of CO2 is the vast lakes of liquid CO2 at the bottom of the oceans sourced by thousands of volcanic vents. Maybe.

      • andrewsjp: “the real source of the increase of CO2 is the vast lakes of liquid CO2 at the bottom of the oceans”

        Here you go!

        Rare Carbon Dioxide “Lake” Found Under the Ocean, Scientists Report

        A team of scientists based in Japan and Germany has found an unusual “lake” of liquid carbon dioxide beneath the ocean floor.

        On Earth’s surface carbon dioxide (CO2) is normally a gas, but in the cold, high-pressure ocean depths it cools and becomes a liquid.

    • Clearly assuming an acceleration in the rate of CO2 accumulation in the air not in evidence.

      Rounded to nearest digit, Hawaiian observations go from 316 ppm in 1959 to 401 ppm in 2015, for an average of ~1.5 ppm per year. That would mean about 528 ppm in 2100. But assume twice that much, since the gain might be around 3.0 ppm this year. In that case, earth would benefit from only 655 ppm by the end of this century. But even in the highly unlikely event that the CO2 growth rate should double from 3.0 ppm to 6.0 on average for the rest of the century, that still only gets us to 911 ppm.

      The accumulation rate might well slow down, as relatively more gas and less oil and coal are burned and alternative sources of energy are adopted.

      • If CO2 growth rates have doubled, doesn’t that imply that the various attempts to install alternative energy sources world over, have been an abject failure?

    • I want to see the basis for making the prediction that quadrupling the CO2 level in the atmosphere through the combustion of anything is even remotely possible.

      Having failed at that, let’s see the plan for tripling it. When that fails, let’s see a plan that might double it.

      Pick a resource, pick a use rate, pick a sink rate, plot the curve.

      I call BS on mankind quadrupling the CO2 level of the atmosphere on this planet.

  2. This study confirms that drought will intensify in many regions in the future

    I didn’t see the confirmation part for this. How does it confirm? Rain wasn’t perfectly aligned with past El Nino events and usually occurs in the year following a peak in my humble experience, which only dates back to 1965 in CA. Is the data for this assertion presented elsewhere?

    • That would account for near record rains across Australia in the last few months, and still ongoing this week! Normal weather following strong El Ninos. Broome, in Australia’s Northwest, had their highest August rainfall in 97 years.

      • Richard I hope you’re right just because I’m living on the west coast of the US these days (eastern Pacific) and even though we had rain in the Santa Cruz mountains this morning we’re not getting a lot of moisture in one of my favorite wine growing regions of central CA and we need it. San Lois Obispo has been a bit dry for the past 2 years and I’ve been looking at historical rainfall following “major” El Nino events in the past, like 1983, 1998, and perhaps 2015. In the winter following the ’83 event we had torrential rains that caused mudslides. Same thing in ’98. So I’m sort of hoping for a La Nina effect this winter.

        And I really mean “sort of”, because when it happened the last two times it was big. Huge might be a better word. Very wet for a very long time. In a very real sense I’m not looking forward to this winter. I’m getting too old for this sh*t :)

        Best Regards.

  3. So, 37% of the land will have more drought. However, the plants in those areas will be more drought resistant, so the area that is effected by drought will come down further (let’s be generous and say 30% of land area). However, on top of that the water needed for irrigation will decrease and the water that passes from rainfall into rivers and streams will also decrease since plants in general will use less, meaning we will have more water available for non-farm uses. In other words, we will be able to fully mitigate drought through freed up resources.
    So in other words, increasing atmospheric CO2 might make drought a thing of the past.

    • “In other words, we will be able to fully mitigate drought through freed up resources.” Calculations to support that statement?

    • I thought they were saying that 70% would see a decrease in rain, but due to the fact that CO2 helps plants conserver water, on only 37% would plants suffer because of it.

      • As far as I could tell they were saying that 70% would see a decrease in rain, but 37% would see a reduction in available water resources. That is, in many areas the decrease in rainfall will more than be made up by less water use in plants. In these areas river water will increase even with less rainfall. In the remaining 37% you would have plants that are naturally more drought tolerant meaning the decrease in available water resources will not have the same impact as currently. In these cases the effective threshold for drought as opposed to mild dry condition will be changed as well.
        At least that is how I read it.

  4. “This study confirms that drought will intensify in many regions in the future,” said coauthor James Randerson, UCI professor of Earth system science.


    “The study confirms that models suggest that drought will intensify in many regions in the future,” said Reasonable Skeptic an guy with a keyboard who had to correct a UCI professor of Earth System Science.

    • It has been confirmed independently by a number of studies. The same studies also confirmed an ice-free Arctic ocean in 2016.

    • Not the part about plants with access to higher pCO2 being more drought tolerant. But that was already known. The junk science is that will somehow feedback to more droughts.

      Even the IPCC in AR5 is ambivalent on drought prevalence and higher pCO2.

      ““In summary, the current assessment concludes that there is not enough evidence at present to suggest more than low confidence in a global-scale observed trend in drought or dryness (lack of rainfall) since the middle of the 20th century due to lack of direct observations, geographical inconsistencies in the trends, and dependencies of inferred trends on the index choice. Based on updated studies, AR4 conclusions regarding global increasing trends in drought since the 1970s were probably overstated. However, it is likely that the frequency and intensity of drought has increased in the Mediterranean and West Africa and decreased in central North America and north-west Australia since 1950”

      • If the rate of transpiration decreases, this could lower the amount of water in the atmosphere which could possibly result in a decrease in rainfall.
        On the other hand, since water is the most potent of greenhouse gasses, a decrease in the amount of water vapor in the atmosphere would result in a significant cooling.
        Evaporation from the ground would be sped up by lower relative humidity in the atmosphere, but slowed down by lower temperatures.
        It’s complicated.

  5. Recent studies have estimated that more than 70 percent of our planet will experience more drought

    The IPCC’s AR4 Report says:

    For a future warmer climate …. Globally averaged mean water vapour, evaporation and precipitation are projected to increase.

    Hardly a recipe for more drought.

  6. I will admit that “this study” has shown me that the old Indian prayer still has meaning and a place in the reality of climate studies – “Open my eyes so I might see.” Somehow, these “miracle workers” we call climate scientists are still looking at the world, the climate, and the data with “eyes wide shut.”

  7. The plant physiology part is hardly news. More CO2, less open stomata in C3 plants, less evapotranspiration, greener Sahel. That CAGW will increase future drought is rank speculation.

  8. Climatists have a sneaky habit of slipping in a silver (or maybe it’s lead) lining into their CAGW narrative, in order to make it look like they are doing some actual science. It’s really qite clever.

  9. This is absurd. We’ve known forever that more co2 increases vegetative matter, plant size and drought resistance. We’ve studied the effects of co2 on plants in greenhouses. We’ve seen the effect in satellite studies of the Earths vegetation over the last 50 years. Plant productivity has increased 20% due to increased co2 and reducing co2 would cause a 20% decrease in agricultural productivity. This is something global warming alarmists don’t mention.

    Would we decrease co2 in the atmosphere if we could? No. It would devastate agriculture to do so and it would lower temperatures worldwide (albeit trivially) which would cause death of more people. Sure a drop of 0.2 or so degree might not produce much more death but why? Why would we reduce the co2 we have or risk lowering the temperature when we can see dramatic benefits already from the little co2 we’ve put into the atmosphere.

    Looking at it like this is instructive. Instead of looking at the risks of increasing co2 which leads some alarmists to panic and assume the worst let’s see how they respond to a lowering of co2? Do they see the risk of lowering co2? The IPCC already admits that temps up to 1.5C are net positive. So by logic reducing co2 and reducing temperatures would be negative because it would take us farther from the 1.5( formerly 2.0) C inflection point. So would they argue it would be bad to lower co2 as they would have to if they were honest.

    • I still have alarmists who proclaim that the fact that CO2 is good for plants is just a denialist myth.

      • Why are you letting them hang about? Isn’t there a spray you can use? “Raid” for radicals?

  10. Study: plants do worse during drought thanks to decreased CO2 levels….

    …and a sane person would assume that since plants didn’t evolve to die

    CO2 has been limiting

    • What you said seems important. But I don’t think I understand what you are saying. Please explain.

  11. The plant hormone abscisic acid (a weak acid) is active when plant turgor is water stressed. Freely available abscisic acid (otherwise naturally held in leaf’s high pH stroma of chloroplast) makes stomata have a greater response to CO2.

    Blue light wavelength is not only good at opening stomata, but at
    keeping stomata open. This dawn blue light is what let’s plant lift a water (& soluble contents) upward based on open stomata
    completing a transpiration flow.

    Since the % of blue light falls as sun rises the water stress closure of stomata gets into play when temperature might rise.
    This allows plant to avoid heat related excessive water vapor going out from the leaf.

    Meanwhile, red spectrum light is not anywhere near as able as blue light to instigate stomata to open or stay open. Green light, on the other hand, can influence stomata to open; but it needs to be intense (very high photon quantum flux) & high CO2 + abscisic acid are apparently over-riding high green flux when it happens.

    Stomata are not all the same configuration. C3 grass stomata are not like round pores & these grass stomata have evolved to be particularly responsive to opening for early morning blue light; their stomata configuration is more responsive for closing too.

    Plants whose stomata respond minimally to high CO2 & show less drought resilience (despite high CO2) will have the propensity toward (& or a growth phase) high level(s) of the mannose kind of plant “sugar”. Mannose binds phosphate which is integral to guard cells of the stomata closing function; mannose is able to open stomata & I suggest this may be one reason for different plants’ benefit during drought even when high CO2.

  12. That plants require less water under higher CO2 conditions has been known for quite a while. I guess the takeaway here is: UC researchers just “discovered” it and can alleviate some climate change fears.

    Maybe soon UC researchers will “discover” that earth was significantly warmer during the Holocene optimum, and polar bears, butterflies, and humans did just fine.

    And, during the next solar minimum, if climate responds the way some non-climatologists predict, perhaps some researchers will “discover” that a cooler climate than what we are used to is actually a bad thing. Perhaps a little global warming will be welcomed, and Al Gore can take his $300 million and hide somewhere.

    • Meh. Finished reading it. Somehow, through vigorous arm-waving and custom designed computer model output, plants under higher CO2 being more drought tolerant leads to…more severe drought. I missed something. I need to read it again.

      Never mind. I have better things to do.

  13. For those more adept than me at this science thing than me, you may wish to watch short show and school some of the commentators in the comments section. Crowder makes some very good points trying to get through to the indoctrinated.

  14. Funny…
    Their models are telling them and any one else interested that the CO2 concentration increase may have an effect in plants only in a case of a very very extreme anthropogenic effect where the concentration quadruples in a very rapid way…..otherwise no luck there of any ppm increase to be considered as food for plants……..Only possible in a very very extreme AGW scenario…..:)

    I love these models…:)
    The models seem to be more intelligent than the humans..:)


  15. “Recent studies have estimated that more than 70 percent of our planet will experience more drought as carbon dioxide levels quadruple from pre-industrial levels over about the next 100 years.”

    This is total BS. As CO2 partitions 50 to 1 into the oceans, there is not a chance that CO2 will even double let alone quadruple. If you do the 50/1 math you will find that there is not enough available carbon to burn to do more then increase the ppm CO2 by 20%. It is too bad that fools who have no idea what they are talking about get to expose such total trash to the world with the hopes that the uniformed will believe them.

  16. Yawn. It’s the old “CO2 is plant food” meme so beloved of conservatives, free-marketeers, libertarians and other high school graduates.

    When will you folks learn? Plants need sunlight and water. That’s it. Science, people.

    Even sunlight is optional. The hydroponics in my basement are doing just fine, thanks. And before you ask, no, I don’t exhale carbon dioxide in their faces. I’ve got a special rebreather apparatus to prevent that. And I lead a carbon-negative lifesyle.

    So you can stick that result in your precious experimental method, mix it with a soupcon of tobacco and smoke it.

    When will these zombie memes give up and return to the grave already?

    • Did you forget the sarc tag?

      All photosynthesizing organisms, not just plants, need CO2 to make glucose and oxygen. Some such organisms get their CO2 from the water in which they live, others from the air, like terrestrial green plants.

      Cyanobacteria (often wrongly called “blue-green algae”) and eukaryotic algae possess a CO2-concentrating mechanism (CCM).

  17. Precipitation is supposed to increase by about 22% due to doubling of CO2. Yes, this is true.

    Somehow, this also translates into 70% more droughts.

    Okay, there is also supposed to be even more evaporation than the 22% but if the plants are suppressing evapotranspiration due to the stomata being less open, how can there be an increase in evaporation by more than than 22%.

    Climate science depends on just ignoring the basic math whenever it is convenient. Always. always, always.

    Economic used to be called the dismal science. Now climate science trumps it by a factor of 22%.

    Your C3 plants and even your C4 lawn grass, is growing much more efficiently now that there is more CO2. It will only get better.

    • “Economic used to be called the dismal science. Now climate science trumps it by a factor of 22%.”

      But I don’t think the phrase ever meant ‘dismally bad,’ just ‘pessimistic; grim.’

      You’re right though: clisci is the abysmal science.

  18. An if you to a Google search on, “Protein” and “CO2,” you over 100,000 hits starting with:

    Rising CO2 levels reduce protein in crucial ……

    And of course it’s all B.S.

  19. “…“This study confirms that drought will intensify in many regions in the future,” said coauthor James Randerson, UCI professor of Earth system science…”

    It did?

    Making that statement as wild a leap in logic as any of the research trash posing as science over the last few years.
    Climate science; where vague waffle terms and concepts transmute into solid action words for alarmism purposes.

    Climate science ≠ real replicable science.
    Climate science = fiction.

    • Should read: “this study confirms that the computer model still gives the same outputs when fed the same inputs”. Some people apparently think that is counts as reproducibility and that multiple papers using similar computer models that give similar results means something.

  20. “There’s a lot we don’t know, especially about hot droughts,” Swann said

    There’s a lot we don’t know about CO2, except that we know that it’s all bad.

    I presume that Swann is from Flanders and Swann:

  21. How is this dressed up an something new? Try Gerhart and Ward 2010, which discusses this extensively.

    Plant responses to low [CO2] of the past. Gerhart and Ward.

    This response to higher Co2 is a simple result of leaf stomata being able to close up (or the leaf producing less stomata), because the plant does not have to ‘breathe’ so hard to get the same amount of CO2 plant-food. And if the plant is not respiring so much, transpiration is also reduced and the plant loses less moisture. So the C3 plants can grow in more arid conditions, and therefore benefit considerably from increased CO2.

    An important thing to note is that this beneficial effect only applies to C3 plants, so if you are growing maize or sugarcane the increasing Co2 has little effect.

    I took this truism one stage further, by suggesting that low CO2 conditions during glacial maxima created new CO2 deserts in China and Mongolia. The Gobi is a high and dry plateau that is highly susceptible to low Co2, in the opposite manner to this paper’s conclusions. And when the entire Gobi becomes a permanent shifting-sand CO2 desert, the northern ice sheets get covered in dust; the albedo is lowered; the ice sheets melt; and the ice age ends. Thus ice ages are ended by low CO2 and the CO2 deserts that this forms. Simple really.


  22. The modelers are quite vocal in their declarations that their models cannot make regional projections. (This is because the regional projections differ from reality by an even larger amount than do the global projections.)
    Yet still the alarmists keep insisting on telling us what the regional impacts of CO2 are going to be.

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