Why should we worry about Climate Change?
Climate change caused by emissions of greenhouse gases (GHGs) from human activities is one of the greatest 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 atmobout 1750, thesphere. Since a concentration of CO2 has risen from about 280 parts per million by volume (ppmv) to reach 377 ppmv in 2004 — a value that has likely not been exceeded during the past 20 million years. CO2 is a "greenhouse gas" (GHG) that captures heat and warms the atmosphere.
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 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 Third Assessment Report (2001) 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 1.4 to 5.8°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 global average surface temperature has already risen by approximately 0.6°C over the past century, a warming trend unprecedented in the past millenium. The IPCC concluded that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations."
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: it is likely, for example, that there has been about a 40% decline in Arctic sea-ice thickness during late summer to early autumn in recent decades. 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.
A key finding of the International Symposium on the Stabilization of GHG Concentrations (2005) was that research completed since the publication of the IPCC's Third Assessment Report has led to "greater clarity and reduced uncertainty about the impacts of climate change... In many cases the risks are more serious than previously thought."
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.
The Need for Deep Emission Reductions
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. Research shows that if we are serious about keeping within this limit, we need to adopt an objective of stabilizing atmospheric GHG concentrations at 400 ppmv of CO2 equivalent.
Meeting this objective requires that global GHG emissions fall to at least 30-50% below the 1990 level by 2050, and that industrialized countries reduce their emisions by 25-30% between 1990 and 2020 and by 85-90% between 1990 and 2050. Given the scale of this challenge, any economically rational strategy will immediately initiate an emissions trajectory that leads to deep reductions.
Source: Envirolink Network