Rising heat weakens plants' ability to absorb CO2, study warns

Are plants losing their ability to store carbon as the world warms?

A study from the University of Arizona has found that rising temperatures reduce vegetation's capacity to absorb carbon dioxide. The research demonstrates that as global temperatures increase, plants themselves heat up faster, triggering thermal stress that weakens photosynthesis and carbon sequestration. This discovery has significant implications for climate strategy, because it reveals a dangerous feedback loop: warming reduces natural CO2 absorption just when atmospheric concentrations are at record levels.

The mechanism is straightforward. Plants have optimal temperature ranges for photosynthesis. When ambient temperatures exceed these thresholds, enzyme activity slows, stomata close to prevent water loss, and the plant's ability to convert sunlight and CO2 into biomass declines. In regions already experiencing heat stress, from Mediterranean forests to tropical rainforests, this effect is most pronounced. The University of Arizona team found that even moderate temperature increases beyond historical norms measurably suppress CO2 uptake in major vegetation types.

This matters because the global carbon budget is already tight. Trees and crops currently absorb roughly a quarter of all human CO2 emissions. If that fraction falls due to thermal stress, the atmospheric burden grows faster, requiring steeper cuts elsewhere. For the UK, which has committed to net zero by 2050, the implication is clear: we cannot rely on nature alone to offset our carbon debt. Active offsetting through verified schemes becomes more essential, not less.

What does this mean for UK carbon offsetting strategy?

The University of Arizona finding underscores why carbon markets and active offset projects remain critical. Tree-planting initiatives are valuable, but they are not a substitute for emissions reduction at source and for investment in projects with guaranteed, measurable carbon removal. Renewable energy projects, landfill methane capture, and advanced forestry management all deliver carbon abatement independent of temperature fluctuations. When natural sinks weaken, these engineered solutions become more vital.

UK policy and corporate net zero targets must account for this reality. Some organisations have factored natural CO2 uptake into their climate plans, assuming forests and agricultural land would absorb a percentage of residual emissions. If plant absorption capacity declines, those assumptions shift. The risk is that net zero targets become harder to meet without deeper cuts and greater reliance on high-quality carbon offset schemes.

For UK individuals and businesses, the message is twofold. First, reduce emissions at source. Second, offset the remainder through verified programmes. Offset Britain helps both audiences do this. Individual subscriptions start from £5.99 a month and support renewable energy and forestry projects vetted to high standards. Businesses can offset from £566 a year, with schemes tailored to supply chain and operational emissions. By taking action now, UK organisations can insulate themselves from the carbon absorption shortfall the Arizona study reveals.

How verified carbon projects differ from relying on natural uptake

Natural carbon sinks, forests, and soils are vital for long-term climate stability. However, they are increasingly unreliable in a warming world. Verified carbon offset projects, by contrast, are designed with defined baselines, additionality tests, and third-party monitoring. A renewable energy project, for example, directly displaces fossil fuel use. Methane capture from livestock or landfills prevents emissions that would otherwise enter the atmosphere. These interventions do not depend on temperature, rainfall, or the health of plant tissues.

The University of Arizona research reinforces why diversification matters. Organisations should pursue emissions cuts, invest in renewable infrastructure, and offset unavoidable residual emissions through a portfolio of verified projects. Relying solely on tree-planting or hoping that nature will absorb carbon faster than we emit it is no longer credible climate strategy. The science is now clearer: plants under heat stress contribute less to the solution.

Written and reviewed by the Offset Britain editorial team. Last reviewed 26 July 2026.

Sources & Methodology

1. Carbon Herald: Rising Temperatures Prevent Plants From Absorbing CO2, Study Finds
2. Offset Britain: Individual carbon offset subscriptions
3. Offset Britain: Business carbon offsetting

Photo by Altaf Shah.