Climate is defined as the weather conditions prevailing in an area over a long period of time. Global climate change is the long-term alteration of weather patterns in the planet that results in elevated temperature, carbon dioxide (CO2) levels, changing rain and wind patterns, melting of glaciers and rising seawater levels. Climate models predict that the global average temperature will rise by 0.2 ˚C in the next two decades in every climatic zone including tropical, temperate, and polar regions.
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create energy in the form of sugar and produce molecular oxygen as a by-product. The carbon cycle in the earth is driven by this process of photosynthesis. This reaction happens mainly in green plants and in some other photosynthetic microorganisms. There are mainly two steps in the photosynthetic process. The first one is the light-dependent reaction where energy is stored in ATP (Adenosine triphosphate) and NADPH (Nicotinamide adenine dinucleotide phosphate) while producing oxygen (O2) as a by-product. The next step is independent of light and is called the Calvin Cycle where sugar molecules are formed by fixing CO2. Furthermore, there are three types of photosynthetic mechanisms called C3 (in cotton, spinach, soybeans, etc.), C4 (in maize, sugarcane, sorghum, etc.), and CAM (in cacti, pineapple, etc.).

CO2 is a greenhouse gas that absorbs longer wavelength radiation and traps heat around the earth’s surface. This phenomenon is known as the greenhouse effect. But when high CO2 levels are present in the atmosphere this eventually leads to excessive global warming.
Carbon dioxide levels today are higher than at any point compared to the past. The levels are rising mostly because of the burning of fossil fuels by humans. The last time the atmospheric CO₂ amounts were this high was more than 3 million years ago. Therefore, we are going back to where plants or small algae began photosynthesis. At the beginning of life on earth, the oxygen concentration was very low in the atmosphere. C3 photosynthesis is thought to have arisen at this time.
The majority of the plant species use C3 photosynthesis in which the first and most stable carbon compound containing three carbon atoms is produced. That’s why it is called the C3 mechanism. The RUBP (Ribulose 1,5-bisphosphate) carboxylase enzyme which catalyzes carboxylation in the Calvin cycle has evolved in the primeval pre-photosynthetic atmosphere which contained high CO2 and no O2. Therefore, this climatic condition is favorable for plants to photosynthesize more efficiently and grow faster which leads to high crop productivity. Under well-watered and highly fertilized conditions, most C3 plants grow about 30% faster when the CO2 concentration reaches 600 – 750 ppm range but a little or no increased growth is seen in C4 plants which fix carbon dioxide into a 4 carbon compounds in order to enter the C3 or Calvin Cycle.
If CO2 concentration continues to increase at this rate, after a particular level plant photosynthetic rate will become limited due to the increase in atmospheric temperature. Under high-temperature conditions, plants tend to close their stomata (microscopic openings in the epidermis of leaves that facilitate gas exchange) to prevent desiccation. In the daytime, photosynthesis happens and thereby CO2 levels are depleted inside the photosynthetic cells and are not restored as stomata are closed. In such situations, the Rubisco enzyme binds with oxygen and leads to a phenomenon called photorespiration. It results in the release of CO2 with the utilization of ATP. This is energetically costly and a wasteful process that happens in C3 plants. Under elevated CO2 levels and high temperature, C4 plants are benefited since they are adapted to warm and high-temperature environments. These plants effectively maintain the CO2 levels in their photosynthetic cells and are adapted to prevent photorespiration.

Even though CO2 is much more important in photosynthesis and increases the rate of reaction up to a certain level the nutrients, and other factors act as limiting factors for the photosynthetic process. Therefore, the photosynthetic rate quickly becomes constrained by the less nutrient availability. Soil is eroded due to the low vegetation cover in lands and most of the nutrients are leaching out from the soil and it becomes poor in nutrients. The presence of pollutants in the atmosphere and low-level ozone can also indirectly reduce the net photosynthetic rate.
A better understanding of the above mentioned phenomena is crucial in studying natural ecosystems, in conserving a balanced ecosystem and in providing high crop productivity to feed the rising human population. If the above mentioned phenomena continue to happen in the future, the C4 and CAM plants may be benefited except the C3 plants even though C4 and CAM mechanisms are more energetically costly than the C3 mechanism. Since most of the plants on the earth are C3 plants, change in global climate patterns has a major influence on the plant community and their survival. Therefore, it is required to minimize these climatic changes while improving plants to adapt to this changing environment. To protect plants from climate change, personal action is more important than ever. Practices such as organic farming, eating less meat, producing clean energy, or even less use of vehicles can help save the planet from climate change and ensure the survival of plants that help us survive on earth.

References:
https://www.nationalgeographic.org/encyclopedia/climate-change/
https://scied.ucar.edu/learning-zone/climate-change-impacts/predictions-
Plant Physiology and Development by Eduardo Zeiger, Lincoln Taiz, Ian Max Moller, Angus Murphy – sixth edition.

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