Why is This Important?
Greenhouse gases, including the largest contributor, carbon dioxide (CO2), are the primary cause of climate change. Greenhouse gases enter the atmosphere through nature’s carbon cycle and human activities such as the burning of fossil fuels and deforestation. Human activities are the main driver of increased greenhouse gases in the Earth’s atmosphere; global atmospheric concentrations of CO2 are now 30 percent higher than they were before the industrial revolution.
What is a Sustainable State?
In a sustainable state, humans have reduced greenhouse gas emissions to a level that is in balance with nature’s ability to absorb those emissions.
How Are We Doing?
· Countywide greenhouse gas emissions totaled 5.6 million metric tons of carbon dioxide equivalent in 2009. Total greenhouse gas emissions were about 4.6 percent lower than in 2008. Most of the reduction was due to reduced electricity and natural gas usage, as well as a reduction in the emissions factor of PG&E’s delivered electricity.
· On a per capita basis, greenhouse gas emissions decreased in 2009 to 7.4 metric tons per capita, down from a peak of 8.4 metric tons per capita in 2003.
· On-road transportation is the largest contributor to greenhouse gas emissions in the county, accounting for 53 percent of all GHG emissions in 2009. Emissions from this source have been decreasing though, down 13 percent since 2000 largely because of decreased miles traveled on area roads.
Electricity and Natural Gas
After transportation, electricity and natural gas use account for the majority of remaining greenhouse gas emissions. Emissions from electricity are driven by both total electricity use and the “carbon content” of the generation source of that electricity, which varies annually based on the amount of renewable generation from hydroelectric power and other non-carbon sources. In 2009, total greenhouse gas emissions from electricity and natural gas use declined 8 percent. The decrease was due to both reduced demand, as well as a “cleaner” energy mix from increased hydroelectric power generation after two consecutive years of drought.
Methane is released from landfills as organic matter decomposes and is an extremely powerful greenhouse gas (21 times more global warming potential than carbon dioxide). In 2009, waste generated in the county accounted for an estimated 100,000 metric tons of CO2e in the atmosphere. Landfill methane has been decreasing steadily since 2000, in line with reduced waste disposal in landfills and increased diversion rates in the county.