Greenhouse Gases

Climate change is one of the most profound threats to people, economies and ecosystems in the 21st century.

Human activities have caused a dramatic increase in the amount of carbon dioxide (CO₂) in the earth's atmosphere. Since about 1750, the concentration of CO₂ has risen from about 280 parts per million by volume (ppmv) to reach 383 ppmv in 2007 — a value that has likely not been exceeded during the past 20 million years. CO₂ is a "greenhouse gas" (GHG) that traps the sun's heat, warms the atmosphere and changes our climate.

The main causes of increasing CO₂ concentrations are the burning of fossil fuels — coal, petroleum products, natural gas — and deforestation. Various industrial, transportation and agricultural activities are also responsible for increases in the atmospheric concentrations of other GHGs, such as methane and nitrous oxide.

Scientific Concern

By 1988, governments had become sufficiently concerned about climate change to establish the Intergovernmental Panel on Climate Change (IPCC). The IPCC's mandate is to advise governments on the science of global climate change caused by GHGs from human activities, and on how to prevent it. The IPCC's reports are authored by hundreds of the world's most respected physical and social scientists specializing in climate change.

The IPCC's Fourth Assessment Report (2007) concluded that if no explicit action is taken to curb GHG emissions from human activities, the global average surface temperature is projected to increase by 1.1 to 6.4°C between 1990 and 2100. Temperature increases like these are not small: the difference in global average surface temperature between the last ice age and today is only about 4 to 6°C.

The IPCC concluded that the global average surface temperature has already risen by approximately 0.7 °C over the past century, and that the “warming of the climate system is unequivocal”. The IPCC concluded that “[m]ost of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic [human-caused] greenhouse gas concentrations.” The IPCC defines “very likely” to mean over 90% certain.

Impacts of Climate Change

The IPCC attributed a wide range of observed impacts to the global warming that has already occurred. Some of these impacts are spectacular: for example, there has been a loss of over 20% in the area covered by Arctic sea ice in summer since 1978. The IPCC has shown that just 2°C of additional warming would suffice to take the world into the realm of risks to many ecosystems and a large increase in extreme events such as storms, floods and droughts.

Examples of impacts likely to occur during this century if GHG emissions are allowed to continue rising unchecked include:

• sea level rise sufficient to flood areas inhabited by millions of people
• more intense rainfall events and tropical storms
• tens of millions of additional people at risk from coastal flooding and hunger, hundreds of millions from malaria and billions from water shortage
• a significant proportion of land-based species "committed to extinction"
• additional annual costs in the tens of billions of dollars for the world’s water management, agriculture and forestry sectors
• a decline in the extent of sea-ice around the North Pole in summer by more than 50% and a threat to the cultural survival of some Arctic communities
• destruction of more than half of the world’s coral reefs; and
• in Canada, reduced water quantities from the Great Lakes to the Rockies.

Given these projected impacts, there is now quite wide support, both in the scientific community and among governments, for defining "dangerous" climate change as a rise in the global average surface temperature of 2°C above the pre-industrial level.

The Need for Deep Emission Reductions

Staying within the 2°C limit will require that global GHG emissions fall to at least 50% below the 1990 level by 2050, and that developed countries reduce their emissions by 25-30% below 1990 levels by 2020 and 85-90% below 1990 levels by 2050. Given the scale of this challenge, developed countries must start immediately down a path to deep reductions. Any delay will almost certainly result in greater costs over the long term.

For more information, please read Pembina's report The Case for Deep Reductions.

External Sources of Additional Information

• The IPCC's Fourth Assessment Report (2007)
  
• Avoiding Dangerous Climate Change — containing the findings of the International Symposium on the Stabilization of GHG Concentrations (2005)
• Joint statement of the national science academies of Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the United Kingdom and the United States (2005)
• Arctic Climate Impact Assessment (2004)