CO₂ Feeds Plants – and Warms the Planet

By Franch Hagerup. Editorially rewritten and fact-checked.

Carbon dioxide sits at the centre of a surprisingly confused public argument. Plants need CO₂ to grow, people and animals exhale it, and the gas is part of Earth’s natural carbon cycle. At the same time, rising atmospheric CO₂ is the largest long-lived driver of today’s global warming.

Those statements are not contradictory. They describe different properties of the same molecule.

CO₂ is plant food – and a greenhouse gas

During photosynthesis, plants use sunlight to combine carbon dioxide and water into sugars. Oxygen is released as part of the process. Without atmospheric CO₂, the ecosystems on which people and animals depend would not function as they do today.

The climate concern is not that CO₂ is a poison at ordinary outdoor concentrations. It is that the molecule absorbs and re-emits infrared radiation. Earth receives energy from the Sun and releases some of it back towards space as heat. Greenhouse gases slow part of that heat loss.

The natural greenhouse effect keeps Earth warm enough for life. Increasing the concentration of greenhouse gases strengthens that effect and changes the planet’s energy balance.

How can such a small concentration matter?

Carbon dioxide is measured in parts per million. NOAA’s global estimate was about 428 ppm in July 2026, roughly 0.043 per cent of the atmosphere. That sounds tiny, but a substance does not need to make up a large share of a system to have an important effect. What matters is how its molecules interact with radiation and how their concentration changes over time.

NASA reports that atmospheric CO₂ has risen sharply over the past century and is now about 50 per cent above its 1750 level. The long-term increase is driven mainly by the burning of coal, oil and gas.

A greener Earth does not settle the climate question

One point made by critics of climate policy is correct: additional CO₂ can stimulate photosynthesis. Research highlighted by NASA found significant greening across parts of Earth’s vegetated land between 1982 and 2015, with CO₂ fertilisation playing an important role.

But plant growth is constrained by water, temperature, nutrients, soil conditions, land use, pests and extreme weather. Greening in one place does not guarantee healthier ecosystems or higher crop yields everywhere. NASA has also reported that many land ecosystems are becoming less efficient at absorbing additional CO₂ as concentrations rise.

The fertilisation effect is real. It does not cancel the warming effect.

Climate has always changed – so what is different now?

Earth’s climate changed long before cars and power stations existed. Ice ages, volcanic eruptions, changes in solar output, orbital cycles and ocean circulation have all shaped the planet’s history.

The relevant question is therefore not whether natural variability exists. It is which causes best explain the rapid global warming observed today. The Intergovernmental Panel on Climate Change concludes that human activities, principally greenhouse-gas emissions, have unequivocally caused the observed warming since the pre-industrial period. Natural drivers alone do not reproduce the measured trend.

Individual hot or cold weather records cannot answer that attribution question. Climate is assessed through long-term patterns across many independent measurements.

Climate science and climate policy are different debates

People can reasonably disagree about carbon taxes, subsidies, regulations, deadlines and the distribution of costs. A policy does not become effective merely because it is presented as climate action.

However, criticism of a tax or a political institution does not change the measured physical properties of CO₂. A productive debate separates three issues:

• What do atmospheric and temperature measurements show?
• What risks and uncertainties follow from those observations?
• Which responses are effective, proportionate and fair?

A previous Ponett opinion piece, “The Climate Is Behaving as Expected”, emphasised atmospheric rivers and other natural processes. These mechanisms are real and important. They operate alongside human influence, not as an alternative to it.

The useful conclusion is the nuanced one

CO₂ supports photosynthesis and warms the climate. Higher concentrations can help some plants under favourable conditions while increasing stress through heat, drought and other climate impacts. Natural variability continues to shape weather even while human emissions drive the long-term warming trend.

A serious climate debate does not need slogans about a harmless “life gas” or a poisonous substance. It needs accurate distinctions between biology, atmospheric physics and public policy.

Sources

• NOAA Global Monitoring Laboratory: global CO₂ observations
• NASA: Carbon Dioxide – Earth Indicator
• NASA: CO₂ is making Earth greener – for now
• NASA: Land ecosystems are becoming less efficient at absorbing CO₂
• IPCC AR6 Synthesis Report: Summary for Policymakers