PricewaterhouseCoopers (PwC), a global services company, has been conducting GHG emissions verifications for the past 10 years in various sectors, including energy, chemical, metals, semiconductors, and pulp and paper. PwC's verification process involves two key steps:

1. An evaluation of whether the GHG accounting and reporting methodology (e.g. GHG Protocol Corporate Standard) has been correctly implemented

2. Identification of any material discrepancies

The GHG Protocol Corporate Standard has been crucial in helping PwC to design an effective GHG verification methodology. Since the publication of the first edition, PwC has witnessed rapid improvement in the quality an verifiability of GHG data reported. In particular the quantification on non-CO2 GHGs and combustion emissions has dramatically improved. Cement sector emissions verification has been made easier by the release of the WBCSD cement sector tool. GHG emissions from purchased electricity are also easy to verify since most companies have reliable data on MWh consumed and emission factors are publicly available.

However, experience has shown that for most companies, GHG data for 1990 is too unreliable to provide a verifiable base year for the purposes of tracking emissions over time or setting a GHG target. Challenges also remain in auditing GHG emissions embedded in waste fuels, co-generation, passenger travel, and shipping.

Over the past 3 years PwC has noticed a gradual evolution of GHG verification practices from "customized" and "voluntary" to "standardized" and "Mandatory." The California Climate Action Registry, World Economic Forum Global GHG Registry and the forthcoming EU ETS (covering 12,000 industrial sites in Europe) require some form of emissions verification. In the EU ETS GHG verifiers will likely have to be accredited by a national body. GHG verifier accreditation processes have already been established in the UK for its domestic trading scheme, and in California for registering emissions in the CCAR.