A key policy argument in favor of emissions markets (relative to command-and-control types of regulation) is their ability to aggregate dispersed information and generate price signals to guide firms' trading and abatement decisions. We investigate this argument in a multi-period model where firms receive noisy private signals about their current period emissions and privately observe their previous period emissions before this information is made public to the rest of the market. Firms respond to information by trading and abating emissions. We show that there exists a rational expectations equilibrium that fully aggregates firms' private information, justifying the policy argument in favor of emissions markets, in the absence of other frictions. We also derive predictions about how prices should be reacting to new private or public information and show that the possibility of abatement dampens the impact of shocks on prices. Finally, we show that the information aggregation result breaks down if firms' abatement costs are also private information.