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Plants and photosynthesis

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How plants and global warming are linked

The rate of photosynthesis depends on the volume of CO2, the intensity of light and the temperature, as well as water availability. If any of these things is compromised or increased, then it becomes the limiting factor. There are limiting factors in the rate of transpiration too.

For this reason, an increase in greenhouses gases and subsequent temperature rises are having an impact on photosynthesis. However, the rate of photosynthesis is also having an impact on the rate of global warming.  

  • Plants are carbon sinks and can help to reduce global warming: 

As plants use carbon dioxide for photosynthesis, and carbon dioxide is a greenhouse gas, photosynthesis helps to reduce the greenhouse gases in the atmosphere. That is why many organizations are choosing to plant trees to reduce global warming. This is called reforestation and can sometimes be called carbon offsetting, and it is a key strategy to help reach net zero.  

As plants take in carbon dioxide, they are known as carbon sinks. The more carbon sinks, the closer we will be to reaching net zero. 

Plants releasing oxygen through photosynthesis also ensures that there is enough oxygen for animals to breathe and use for respiration. 

Net zero strategy
  • Increased temperatures are making leaves too hot: 

Leaves have adapted over time to be flat and have a large surface area so that they can capture sunlight for photosynthesis. However, this means that they are also susceptible to heat stress, which is more likely due to by global warming. 

To allow the chemical reaction of photosynthesis to take place, there are lots of different proteins called enzymes inside the leaf. All of these need a particular temperature to work well.  

If the temperature is too hot, these enzymes can denature. This is likely to happen during a heat wave which makes the temperature very different to what it is usually. These weather events are becoming more common due to global warming.  

If the enzymes denature, then photosynthesis cannot happen. This means that the plant cannot make it’s own food anymore and may die.  


  • Global warming is reducing water availability:

Water is needed for photosynthesis; it is a reactant in this chemical reaction. Without it, photosynthesis cannot happen.  

However, the increased temperatures from global warming are altering the water cycle and making droughts more likely. 

As plants cannot photosynthesize without water, this means that the plants die. 

As global warming can reduce the effectiveness of photosynthesis, and plants are needed to reduce global warming, this is a self-perpetuating cycle.

Plants die as they cannot photosynthesize which means that less CO2 can be removed from the atmosphere.  


  • Global warming can alter transpiration:

Increased temperatures can increase the rate of transpiration which can lead to water shortages, especially in areas of drought.

However, in some plants the guard cells close their stomata at high temperatures to prevent excessive water loss and to maintain the remaining water stores. Though this conserves the water availability, this protective mechanism can also mean that CO2 cannot enter and therefore photosynthesis cannot occur.



House of Commons Library (2023) Government policy on reaching Net Zero by 2050. Available at: (Accessed: 11/10/2023)