Pep focuses on collaborative and highly integrative research to develop national, continental, and global budgets and trend analyses of the main greenhouse gases, including carbon dioxide, methane, and nitrous oxide. He also studies the size and vulnerability of Earth’s carbon sinks and pools, carbon-climate feedbacks, and pathways to net-zero emissions, including land-based carbon sequestration and negative emissions. More recently, he has also focused on abrupt impacts and ecosystem collapse in response to climate change, particularly wildfires. He uses a robust understanding of regional and global biogeochemical cycles to inform the formulation of sub-national, national, and international policy and actions to mitigate climate change.

Pep has contributed to the United Nations - Intergovernmental Panel on Climate Change (IPCC) for the last 18 years (AR4, AR5, AR6) and multiple assessments of the World Meteorological Organization. He is a fellow member of the American Geophysical Union, and Reuters named him the 8th most influential climate scientist in the world in 2021. Pep has co-authored over 240 peer-reviewed research papers (Web of Science), with 60 papers in Nature journals and Science; he has also edited 18 books and special research journal issues. His published work has attracted over 100k citations in the scientific literature, and has been a Highly Cited Researcher in Environment & Ecology and/or Geosciences every year since 2017. Pep is also a keen science communicator with engagement in national and international traditional media, social media, and evidence-based journalism at The Conversation with over 1.7 million reads.