Capital flows in primary markets are key to the low-carbon transition, as capital raised can finance low or high-carbon assets. Yet, fund-level climate-related disclosures have focused on portfolio holdings, reducing the ability of investors to evaluate the impact of capital flows. In particular, as passive funds grow, there is a risk that capital is channelled into carbon-intensive assets through primary markets. To track carbon-intensive portfolio holdings and primary market transactions, and the role of passive funds within them, we construct a dataset of daily holdings for passive U.S. corporate bond exchange-traded funds (ETFs) from 2016 to 2021. We find that the carbon exposure and carbon intensity of ETF primary market transactions are associated with existing ETF portfolio holdings. We also find that the share of secondary market holdings and primary market transactions accounted for by passive ETFs is higher for fossil fuel bonds, and increases with bond-level carbon intensity. These findings indicate that the continued growth in passive funds could support carbon-intensive capital flows.

初级市场的资本流动是低碳转型的关键，因为筹集的资金可以为低碳或高碳资产提供资金。然而，基金层面的气候相关披露主要集中在投资组合持有量上，降低了投资者评估资本流动影响的能力。特别是，随着被动基金的增长，资本有可能通过一级市场流入碳密集型资产。为了跟踪碳密集型投资组合持有量和一级市场交易，以及被动基金在其中的作用，我们构建了 2016 年至 2021 年被动型美国公司债券交易所交易基金 (ETF) 的每日持有量数据集。我们发现碳ETF 一级市场交易的风险敞口和碳强度与现有 ETF 投资组合持有量相关。我们还发现，化石燃料债券的被动 ETF 在二级市场持有量和一级市场交易中所占的份额更高，并且随着债券碳强度的增加而增加。这些发现表明，被动基金的持续增长可以支持碳密集型资本流动。