The GAO found that the cap-and-trade scheme sucessfuly created a working carbon market, "but its effects on emissions, the European economy, and technology investment are less certain." The report noted that the use of carbon offsets can "undermine the system's integrity" because there is no way to ensure that the projects invested in would not have been built anyway, or that they will last long enough to reduce the amount of emissions that they are expected to reduce. Carbon offsets, the report concluded "involve fundamental tradeoffs and may not be a reliable long-term approach to climate change mitigation."