The integration of the international carbon market is analyzed using a time-varying parameter vector autoregressive (TVP-VAR) model to assess the connectedness and spillover effects among major emission trading schemes (ETSs). The study focuses on four ETSs: the European Union ETS (EU ETS), California Cap-and-Trade (CA-CaT), Hubei ETS (HB-ETS), and New Zealand ETS (NZ-ETS). The TVP-VAR model allows for dynamic estimation of return and volatility spillovers, capturing time-varying relationships between markets. The results show that the total connectedness index is around 10–12%, indicating relatively low spillover effects compared to other market integration studies. The EU ETS consistently acts as a net transmitter, particularly in return connectedness, while the NZ ETS emerges as a major shock receiver in both return and volatility systems. The study highlights the dynamic nature of spillovers, especially during the energy crisis and the Covid-19 outbreak. Global climate negotiations and carbon market events have a minor impact on connectedness, whereas energy or financial crises and the Covid-19 outbreak have a more significant effect. The findings provide insights into the intricacies of carbon price volatility and market transmissions, offering valuable information for investors and policymakers. The study also reveals that the EU ETS is the largest market in terms of scale, while the HB ETS is the smallest and has the lowest carbon price. The results emphasize the importance of understanding the time-varying nature of spillovers and their drivers, including economic growth, government policies, international climate agreements, and extreme weather events. The study contributes to both academic and practical understanding of carbon markets, highlighting the need for further research on the asymmetric effects of spillovers and the role of policy changes in shaping market dynamics.The integration of the international carbon market is analyzed using a time-varying parameter vector autoregressive (TVP-VAR) model to assess the connectedness and spillover effects among major emission trading schemes (ETSs). The study focuses on four ETSs: the European Union ETS (EU ETS), California Cap-and-Trade (CA-CaT), Hubei ETS (HB-ETS), and New Zealand ETS (NZ-ETS). The TVP-VAR model allows for dynamic estimation of return and volatility spillovers, capturing time-varying relationships between markets. The results show that the total connectedness index is around 10–12%, indicating relatively low spillover effects compared to other market integration studies. The EU ETS consistently acts as a net transmitter, particularly in return connectedness, while the NZ ETS emerges as a major shock receiver in both return and volatility systems. The study highlights the dynamic nature of spillovers, especially during the energy crisis and the Covid-19 outbreak. Global climate negotiations and carbon market events have a minor impact on connectedness, whereas energy or financial crises and the Covid-19 outbreak have a more significant effect. The findings provide insights into the intricacies of carbon price volatility and market transmissions, offering valuable information for investors and policymakers. The study also reveals that the EU ETS is the largest market in terms of scale, while the HB ETS is the smallest and has the lowest carbon price. The results emphasize the importance of understanding the time-varying nature of spillovers and their drivers, including economic growth, government policies, international climate agreements, and extreme weather events. The study contributes to both academic and practical understanding of carbon markets, highlighting the need for further research on the asymmetric effects of spillovers and the role of policy changes in shaping market dynamics.