Distinct cap-and-trade systems can be linked together through the mutual or unilateral recognition of emissions allowances for compliance. Linking systems creates a larger carbon market, which can reduce overall compliance costs, increase market liquidity and generate a more stable carbon market. Linking systems can also be politically symbolic as it shows willingness to undertake a common effort to reduce GHG emissions. Some scholars have argued that linking may provide a starting point for developing a new, bottom-up international climate policy architecture, whereby multiple unique systems successively link their various systems.