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Climate-Carbon Interactions in the Current Century

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New tools boost understanding of the perpetual interactions between climate and carbon cycle

The ongoing climate crisis underlines how changes in the carbon cycle can drastically affect our climate. An EU-funded project sheds light on their complex interplay and feedback mechanisms.

Climate Change and Environment icon Climate Change and Environment

Climate-carbon cycle feedbacks, resulting from interactions between the climate and carbon cycle, can amplify global warming. Burning fossil fuels increases atmospheric CO2, causing warming. However, climate changes affect the carbon cycle too. For example, warmer temperatures accelerate organic matter decomposition, releasing more CO2. Moreover, as Earth warms, natural carbon sinks such as forests and oceans may absorb less CO2, creating a feedback loop that exacerbates climate change.

Novel tools tracking CO2 variability and near-term predictions

The EU-funded 4C project was dedicated to enhancing quantitative understanding of carbon-climate interactions and feedbacks. This has been achieved by integrating models and observations, providing new constraints on carbon-climate interactions and climate projections. “We developed new tools and methods to predict, for the first time, the evolution of global carbon cycle variability over the coming decade including atmospheric CO2, land and ocean carbon sinks, and climate response,” notes Kerry Hope, 4C project coordinator. Three European Earth system models (ESMs) were utilised to develop and continually improve model initialisation techniques. These techniques have been validated against new observational products for near-term CO2 predictions. “The best-performing initialisation technique was used to perform near-term predictions. These predictions assume that anthropogenic emissions follow the nationally determined contributions (NDCs) as defined by the Paris Agreement,” explains Hope. “This allows us to anticipate the near-term evolution (from 2020 to 2030) of atmospheric CO2 increase as well as the response of land and ocean sinks to climate change and variability.” Emergent constraints and model skills have been combined to reproduce the historical climate projection records. This combination provides original weighting of multi-model and large ensemble climate and carbon cycle projections. “Our Climate Model Intercomparison Project (CMIP6+) ESMs have been used to explore original adaptive scenarios. These scenarios start with one that aligns with NDCs for the first decade (2020-2030). After this, we implement an adaptive mechanism: every 5 years we simulate climate change and adjust our emission reduction plan accordingly. The goal is to keep global warming below 1.5 or 2 degrees Celsius,” highlights Hope.

Disseminating findings to the broader public

4C has made significant contributions to major international scientific assessments, such as the Intergovernmental Panel on Climate Change Sixth Assessment Report. It has supported the ScienceBrief platform, which synthesises rapidly evolving science on the global carbon cycle. The 4C team has also been strongly involved in the reports included in the Global Carbon Budget project. “By confronting ESMs with novel observations and developing new emergent constraints and model weighting approaches, we sought to increase confidence in climate change projections,” states Hope. “Overall, we provided added value to decisionmakers and policymakers in a bid to sustain Europe’s leadership in climate science.”


4C, carbon cycle, CO2, model, climate change, feedback, carbon sink, ScienceBrief

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