Plants wilting due to heat stress and climate change
Crops wilting in the hot sun. Photo: Courtesy of Wiki Commons

7 Effects of Climate Change on Plants

In this article we look at the effects of climate change on plants and crops. We focus mainly on the effects of rising temperatures and increased concentrations of carbon dioxide (CO2) on plant growth, as well as the impact of water shortages, but we also look at how global warming affects weeds, pests and crop diseases. In addition, we examine how nutrition in plants is affected by increased levels of CO2.

When we speak of plants, we include agricultural crops, trees, shrubs, grasses and other forms of vegetation that photosynthesize nutrients in their leaves with the help of the green pigment chlorophyll, while absorbing water as well as inorganic substances through their roots. We also include marine plants, known as phytoplankton or micro-algae.

Photosynthesis will increase with greenhouse gas emissions. This is one of the effects of climate change on plants.
Diagram of photosynthesis in plants. By taking in water from the roots and carbon dioxide (CO2) from the air, and light energy from the sun, plants create sugar and oxygen. Image: © mapichai

The Main Climate Risks for Plants

Global warming has numerous consequences for plants, including a higher risk of heatwaves, extra flooding, and more intense droughts. In the tropics and sub-tropics natural variations in weather patterns – such as the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) – are likely to become more extreme as temperatures rise.

As well as these knock‐on effects of global warming, the predicted doubling of carbon dioxide concentrations in the atmosphere will have a direct impact on plant growth, reproduction, and endurance.

Predicted increases in mean surface temperatures along with fluctuations in rainfall patterns, may also result in hotter, and drier climate conditions. Scientists expect that in the late 21st century there will be an increase in intensity and/or duration of drought on a regional to global scale 1 . In addition, the contrast between rainfall in wet and dry regions, as well as between wet and dry seasons, will increase.

These meteorological changes are expected to reshape regional climates causing significant shifts in crop production. For example, by 2100, summers in northern U.S. states such as Illinois or Michigan, may be more like those in southerly states such as Texas, or Arkansas.

Better Climate Data Needed

As of August 2020, climate models still lack the ability to cope with the tremendous number of variables that influence how plants are likely to cope with, and respond to, climate change. As a result, scientists still debate the effects on plant growth and crop yields.

Until satellite observations are able to generate more precise data, and botanists are able to fully understand plant responses to rising heat, this debate will continue. All we know for sure, is that unchecked greenhouse gas emissions could have a devastating effect on plants and all other living creatures, including us.

7 Major Effects of Climate Change on Plants & Crops

Here is a short introduction to seven of the most damaging effects of climate change on plant health and crop yields.

1. Effect of Carbon Dioxide on Plants

Record Levels of Atmospheric CO2

As of 2020, levels of atmospheric carbon dioxide (CO2) are running at about 410 parts per million (ppm), slightly less than the May 2019 peak of 414.8 ppm. 2 Since the pre-industrial period, average global levels of CO2 have risen by almost 50 percent. This means that CO2 levels today are higher than at any point in the last 800,000 years. 3

Fertilization Effect of CO2

Atmospheric levels of CO2 are forecast to reach 550 ppm by 2050, which is one of the most important effects of climate change on plants. More CO2 is likely to make all types of vegetation grow bigger and faster, thanks to the so-called “fertilization effect”. Basically, when there is more CO2 in the air, plants can perform more photosynthesis, thus increasing their energy levels and boosting growth. However, this added growth, is typically possible only in the absence of drought or extreme temperatures. 4

The growth response is greatest in C3 plants, such as soybean, wheat and rice, or other C3 crops like carrots, cauliflowers and onions, all of whom increase their leaf area and biomass under elevated CO2 conditions. The response of C4 plants tends to be more muted. (Note: Plants are classified C3 or C4 due to differences in how they photosynthesize. Roughly 95 percent of all plants are categorized as C3.)

Paradoxically, the stress experienced by plants due to water shortage has been observed to be reduced as CO2 increases. This is because high levels of CO2 cause the partial closure of stomata – the leaf pores through which plants transpire – thus conserving water levels within the plant.

Negative Effects on Plants of Increased CO2

Unfortunately, the ‘fertilization effect’ is likely to be offset (in whole or in part) by other, negative consequences. For example, studies have shown that elevated CO2 may reduce the nutritional value of crops through decreased mineral concentration within the seeds. 5

More recent studies have reported an average decrease of 8 percent in several minerals in C3 crops, under elevated CO2 conditions, as well as a 3–17 percent decrease in concentrations of protein, zinc and iron. 6 7

Calculations based on country-level food supply datasets and national food balance sheets for 225 different foods, indicate that these nutritional losses from crops will lead to zinc and protein deficiencies in an additional 175 million and 122 million people, respectively, if the CO2 forecast of 550 ppm by 2050 is maintained. 8 If these calculations are borne out by other studies, nutritional loss would be one of the worst effects of climate change on plants, at a popular level.

Fortunately, contraindications have already been seen, showing that other abiotic factors in combination with elevated CO2, may reduce this decrease in nutritional quality. One study, for instance, shows that soybean plants grown under conditions of elevated CO2 and increased temperatures, largely restore any previously measured decreases in iron and zinc in the seed. 9 This opposing outcome illustrates the complexity of climate change impacts on crop production and quality, and underlines the need for a broad view of all relevant factors.

Also, we should bear in mind that the big picture, as far as crop nutrition is concerned, is the urgent need to increase food production to meet the demand of 9.1 billion people by 2050 – an increase of 2 billion people in 30 years. 10

Plant Growth Caused by CO2 Offset by Other Factors

Climate change is multi-faceted and affects a number of variables that determine how much plants can grow. These variables include extreme temperatures, a decrease in water availability, and changes to soil conditions, all of which impact negatively on plant growth and development.

Overall, the expectation seems to be that climate change will stunt plant growth and crop yield. 11 This is because the number of suitable growing days is forecast to decrease globally by up to 11 percent when all climatic variables that limit plant growth are considered, such as temperature, water availability, and solar radiation.

That said, the effect of climate change on plant growth is likely to vary region by region. A fall in the average number of freezing days, for instance, is likely to boost crop yields in northern countries like Russia, China and Canada. Conversely, extreme heat patterns in already hot tropical regions may lead to fewer growing days per year.

Raised CO2 Linked to Lack of Nitrogen in Soil

Scientists are finding that rising temperatures and increased levels of carbon dioxide in the air, are causing a shortage of nitrogen, a critical nutrient for terrestrial plants. 12 Because if plants cannot get hold of sufficient nitrogen, they can’t produce amino acids, without which they can’t make the special proteins that they need in order to grow. Commercial croplands are typically doused with nitrogen fertilizer, so this nitrogen shortage only applies to non-commercial trees, shrubs and other vegetation.

Map of Global Temperatures 2010 to 2019. Extreme heat is one of the worst effects of climate change on plants.
Map showing average increase in global temperatures from 2010 to 2019 compared to a baseline average from the period 1951 to 1978. Extreme heat is one of the most serious effects of climate change on plants and crops. Data source: NASA, Goddard Institute for Space Studies.

2. Effect of Elevated and Extreme Heat on Plants

Another of the major effects of climate change on plants is heat. This usually leads to higher plant growth and yield. Plant growth in the tropics, for instance, is invariably faster and greater than plant growth in temperate regions.

But, if temperatures exceed the physiological limits of a plant, they will eventually cause higher desiccation rates. A number of plant organisms are already close to their heat tolerance limits and some may not be able to maintain growth if temperatures rise much higher.

The optimum temperature range for C3 crops is 15–20°C and for C4 crops it is 25–30°C.

Rising temperatures also affect plant phenology – that is, the timing of certain plant life-cycle events such as flowering – in a variety of ways. 13 For instance, excessive heat can cause spikelet sterility in rice, destabilize vernalisation in wheat, or reduce pollen viability in maize. Crop yields can be severely reduced if temperatures exceed critical limits for as little as 1 hour during flowering, an important event in crop development.

Crop yields are affected mostly by photosynthesis and by the phenology of crop development. Sometimes, the one is offset by the other. For example, increased photosynthesis (due to raised CO2 levels) typically increases crop yield, but warmer temperatures may reduce the grain-fill period and thus reduce the yield.

Grain yield and above-ground biomass typically decline significantly during periods when temperatures exceed critical limits, especially if accompanied by a water deficit.

Heat Plus Water Shortage Causes Adverse Effects in Plants

A rise in air temperature beyond a plant’s threshold level, may limit its growth and development. Both corn and soybean, for instance, are susceptible to heat (and water) stress during early vegetative stages and during critical growth stages.

When extreme heat stress is combined with a decline in soil water content, the effect on crops – including corn and soybean – is much stronger. Therefore, during periods of extreme heat, soil water content must be maintained at an adequate level, not just to hydrate crops but also to mitigate the effect of higher soil temperature resulting from higher air temperature.

Unfortunately, as global temperatures continue to rise, rainfall patterns are forecast to become more and more extreme, with long dry spells in some areas, dangerous floods in others. The World Health Organization warns that, by 2025, half of the world’s population will be living in water-stressed areas. 14

Water sufficiency isn’t just about how much rain falls – it’s about how fast it falls and how dry the soil is. If it falls very quickly, or the soil is dry and hard, a large percentage of the water will be lost in run-off. That’s why a sudden downpour after a prolonged drought can cause flash flooding – the water simply runs away.

Climate impacts on alpine ice caps may be another danger for plants. In some areas, for example, water reserves built up during the winter may be depleted earlier, as glaciers disappear and snowfall changes to rainfall, as the planet warms. 15 Such water shortages will inevitably impact on plant growth.

Climate change is not only drying out the soil through higher air temperatures, it’s also causing rainfall to become more extreme and more unpredictable. And it’s melting the cryosphere. All of which may have disastrous consequences for soil moisture and water uptake in plants. See also: Why is Soil So Important to the Planet?

When plants experience water deficit, they suffer a variety of adverse effects including cell turgor loss, decreased assimilation of CO2, oxidative stress damage, and nutritional deficits, among others. Plants try to combat these impacts by activating short- and long-term drought resistance mechanisms, ranging from stomatal closure to reduce transpiration, to changes in root architecture, nutrient allocation, leaf/root phenological cycles, cell-dehydration tolerance mechanisms, and so on.

Note also that mild to moderate deficits do not affect harvest index (the ratio of grain yield to total above-ground biomass) – in some species they may even increase it – but severe water deficits do affect it. 16 And if combined with heat stress the impact on crop yield is likely to be significantly greater.

Microburst rain bomb over Phoenix, Arizona
Rain bomb (intense localised downpour) over Phoenix, Arizona. It is just one of the extreme weather effects of climate change on plants. Photo: © Bruce Haffner

3. Effect of Extreme Weather Events on Plants

Extreme weather events can affect crops, too. Climate change alters several of the characteristics of the atmosphere that affect weather patterns and storms. As a result, we’re seeing a marked increase in the intensity and frequency of extreme weather events. For example, the U.S. National Climate Assessment states that in recent decades both the number and intensity of heat waves, severe downpours, and category 5 hurricanes have increased noticeably in the United States. Here are three types of extreme weather events that affect plants.

Hail can have very negative effects on crops. The good news is, climate change is expected to reduce the number of hailstorms, due to a warming troposphere. The bad news is, storms with larger hail stones (40mm/1.6-inches) are expected to become more common. Hail this size can damage glasshouses, which is obviously not good for glasshouse plants, but it also damages tender springtime plant leaves and stems, and can completely kill seedlings. Hail later in the season can reduce harvests by dislodging fruit from trees and plants. 17

Rain bombs (“wet microbursts”) can deluge an area 4 km (2.5 miles) in diameter, with 5-8 cm (2-4 inches) of water in less than an hour, causing flash floods and major damage to homes and other structures. It can flood fields, blast crops and level hundreds of trees. A rain bomb happens when a heavy column of cool air suddenly sinks, pulling its dense water content down with it. Its force is sometimes so great that winds speed can exceed 100 mph.

Droughts are one of the most distressing effects of climate change on plants. Climate change exaggerates the alternating weather patterns caused by the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and other regional weather systems. As a consequence, periods of low rainfall and drought are increasing in both numbers and intensity. As we have already seen, water deficit plus high temperatures can be very damaging for plants and crops.

This is because without enough water, certain biological processes, like photosynthesis, are dialled down, reducing both plant and root growth, and thus crop yield. Water also drives transpiration – the way water and dissolved mineral nutrients are transported from the soil to the rest of the plant. It also enables the plant to cool itself (and its surroundings) by emitting water vapor through its leaves.

A plant suffering from stress – whether water or heat related – is weaker and thus more vulnerable to attack from insects or disease.

Even after a drought has come to an end, it may be months or even years before an ecosystem recovers, and its plants repair damaged root systems and regain their earlier capacity for growth.

Factors that influence the onset and extent of drought damage in plants include: (a) Whether the soil holds water or not – for example, clay soils do, sandy soils don’t. (b) The type of root system a plant has. Extended systems allow the plant to retain more water. (c) Whether or not the plant is surrounded by other plants competing for the same moisture in the soil. The more competition, the tougher it is to survive. (d) The size of the plant’s root system, compared to its above-ground biomass. The larger the root system is, the better.

4. Effect of Weeds, Pests and Diseases on Plants

Weeds are likely to benefit from the same “fertilization effect” as cultivated crops, requiring the use of more herbicides. Pests, too, are expected to proliferate, increasing the demand for pesticides. Neither outcome is in the long-term interest of plants, crops or farmers.

As global warming intensifies, atmospheric humidity is expected to rise significantly. Combined with higher temperatures, this could result in the growth of blight as well as fungal diseases. The same factors are likely to encourage the proliferation of disease-bearing insects.

Map of Arable Farmland in the World
Global map showing the gradual increase in arable farmland as the northern hemisphere warms. Image: © (Myron King et al, 2018)

5. Global Warming Affects Amount of Arable Land for Plants

Climate change is expected to enlarge the total amount of arable land in high-latitude regions of the northern hemisphere through a reduction in the amount of frozen ground. This higher growth potential is one of the more welcome effects of climate change on plants. Temperatures in the circumpolar Arctic are higher now than they have been for 44,000 years, perhaps even for 120,000 years, with some areas warming three times faster than the global average over the past 150 years. 18

A recent scientific analysis says that if climate models are correct, Canada could increase its amount of arable land by a massive 3.1 million sq kms (1.2m sq miles) by the end of the century. Worldwide, it says, the situation may be even rosier. At present, no more than 25 percent of boreal areas grow crops, but by the end of the century, it could be more like 75 percent. An extra 10 million square kilometres could be claimed for farmland, with large gains for Russia, Finland, Sweden, and Kyrgyzstan. 19

Unfortunately, these gains are likely to be offset by losses in arable farmland caused by sea level rise around the world, in countries such as the Netherlands, Bangladesh, China and Vietnam. South East Asia, which is especially vulnerable, risks a major loss of rice crop if seas rise as expected by the end of the century.

6. Effects of Climate Change on Plants in the Ocean

Phytoplankton are the plants of the ocean. They are the main primary producers and serve as the foundation of the marine wood web. Without them, almost all marine creatures would starve. In addition, phytoplankton produce at least 50 percent of the world’s oxygen (maybe more) and absorb around one third of all man-made CO2 in the atmosphere. 20 21

Unfortunately, one of the effects of climate change on the ocean is warmer water and this is already reducing the abundance and primary productivity of phytoplankton. 22

In the North Atlantic, researchers report that phytoplankton’s productivity has fallen about 10 percent since the mid-19th century, a decline which coincides with rising surface temperatures over the same period. 23

According to another study, since 1950, the population of phytoplankton in the world’s oceans has dropped by about 40 percent under pressure from ocean warming. 24

The population and productivity of phytoplankton are both notoriously difficult to estimate due to the sheer scale of the marine environment, but whatever the exact figures, it seems clear that global warming is putting these tiny but vital organisms under great pressure. This is not surprising. Latest research shows that the oceans absorb 93 percent of all the heat produced by climate change. 25

For more about the effects of climate change on marine plants like mangroves as well as kelp forests and coral reefs, see: Effects of Global Warming on Oceans.

7. Effects of Climate Change on Plants’ Respiration

Does climate change increase or reduce rates of plant respiration? This is a key question of great interest to farmers, agricultural scientists, botanists and climate experts.

Plants have a dual role in the carbon cycle: they capture CO2 when they photosynthesize (daytime only), and release CO2 when they respire (day and night). The difference is stored in their leaves and shoots. Changes to either of these continual processes, in response to global warming, have profound implications for the net-contribution of plants to climate change mitigation plans.

Respiration has never been as popular a topic as photosynthesis and yet it shouldn’t be discounted. Because up to half the CO2 captured during photosynthesis is exhaled during respiration. So any change to this process may have serious consequences.

Unfortunately, it’s not clear whether the extra heat and carbon dioxide generated by global warming, increases or reduces respiration in plants.

One recent paper suggests that plant respiration is a larger source of CO2 emissions than previously thought. In this study, loss of carbon dioxide during plant respiration was found to be 30 percent higher than previous estimates. Moreover, researchers say the rate is expected to increase as temeratures rise. 26

This contradicts a slightly earlier study that cast doubt on the assumption that if temperature doubles, so does plant respiration. The study found that respiration decelerated as leaves warmed, suggesting a declining sensitivity to higher temperatures. The finding was replicated across all biomes and plant functional types. 27

Plants and trees serve as a highly efficient carbon capture and storage (CCS) system, and since CCS is fast-becoming a high profile climate action strategy, expect to see a slew of new studies on plant respiration, as improved climate models and satellite refinements come on stream.

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