The sharing of information by governments is central to how the Climate Change Convention works. The Convention requires its members to submit "national communications" to the Conference of the Parties (COP) on a regular basis. This information about national greenhouse gas emissions, international cooperation, and national activities is reviewed periodically so that the Parties can track the Convention's effectiveness and draw lessons for future national and global action.

National communications describe what a Party is doing to implement the Convention. Relevant issues could include policies for limiting greenhouse gas emissions and adapting to climate change, climate research, monitoring of climate impacts on ecosystems and agriculture, voluntary action by industry, integration of climate change concerns into long-term planning, coastal-zone management, disaster preparedness, training, and public awareness.

They also include "national inventories" of greenhouse gas emissions and removals. This data should detail the sources of emissions for each gas, the "sinks" that remove greenhouse gases from the atmosphere (such as forests that absorb carbon dioxide), and the quantities involved. This information should be collected using agreed methodologies to ensure that national data are consistent and comparable and can be incorporated into global data sets.

Developed countries provide additional details on their efforts to limit emissions. These so-called Annex I Parties must describe the policies and measures they are adopting which are aimed at returning greenhouse-gas emissions to 1990 levels by the year 2000. They must also give projections through the year 2000 of how their policies will affect emissions and sinks. Their first submissions were due no later than six months after they became a Party. The initial communications have been single documents, normally with annexes and a brief executive summary. The second submissions are due by 15 April 1997.

The national communications are subjected to a regular review process. A team of experts from developed and developing countries and from international organizations is assembled for each review by the Convention's secretariat. The first review in late 1994 considered 15 communications, while the second one in mid-1996 was based on 33. In addition, review teams have visited developed countries to conduct in-depth reviews; these are comprehensive technical assessments of the information contained in the national communications. A further benefit of the reviews is that they help to build capacity in developing countries through the participation of their experts. The reviews of communications and the in-depth reviews conducted on-site are summed up in a "compilation and synthesis" report that is produced for each meeting of the COP.

The 1996 review of national communications reveals that carbon-dioxide emissions continue to rise in most developed countries. Comparing the data from 1990 inventories with projections for the year 2000 shows carbon-dioxide emissions rising over the decade if additional measures are not adopted. The major exceptions are the countries with economies in transition (Eastern Europe and the former Soviet Union) whose CO₂ emissions declined sharply during the first half of the decade and, though starting to grow again, will probably stay below 1990 levels. For methane, all but three Parties project that their emissions will decline or stabilize over the decade. Nitrous-oxide trends are not clear, although some countries project major decreases.

It also shows that carbon dioxide accounts for 80.5% of total greenhouse-gas emissions from developed countries. Fuel combustion is confirmed as the most important source of CO₂. With the 33 Parties included in the second review accounting for around 63% of the global CO₂ emissions in 1990, this seems to confirm carbon dioxide as the most important greenhouse gas resulting from human activities. While governments generally believe that their data on carbon dioxide have a high confidence level (with the exception of land-use change and the forestry sector), the confidence levels for data on methane and nitrous oxide are medium to low, depending on the sector.

Developed countries are exploring a wide range of climate change policies and measures. The policies governments choose are generally dictated by national circumstances such as political structure and the overall economic situation. Many are "no-regrets" measures that have environmental or economic benefits irrespective of climate change concerns. In addition to regulatory and economic instruments, Parties are promoting voluntary agreements with industry and public authorities. Other measures involve research and development, and information and education.

Specific measures are being used for most of the major economic sectors. Policies for the energy sector (the largest source of emissions for many countries) include switching to low- or no-carbon fuels, reforming market regulations to spur competition, and removing subsidies on coal. Industry-related policies include voluntary arrangements, standards, financial incentives, and liberalized energy prices. The focus in the residential, commercial, and institutional sector is on energy-efficiency standards for new buildings, higher energy prices, and public information campaigns. Agricultural measures include reducing herd sizes and fertilizer use and improving waste management. While most governments project an expansion of the transportation sector, relatively few measures for controlling its emissions were reported.

Developing countries will start making their initial submissions in 1997. Their due date is 36 months after becoming a Party or having access to the necessary financial resources. Parties that are least developed countries may make their initial communications at their discretion. In 1996, the COP adopted the guidelines and format that developing countries should use for these initial communications. It also emphasized to the Global Environmental Facility the need to expedite the approval and disbursement of financial resources so that developing countries can make their submissions on time.

The frequency of future communications by all Parties will be determined by the COP. The COP will also continue to work towards improving the quality and usefulness of the national communications. For example, many methodological and practical problems remain for the calculation of inventories. Scientific uncertainty and data collection both pose serious difficulties, so the Intergovernmental Panel on Climate Change (IPCC) is refining the methodologies used for national communications.