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CURRENT ISSUE: January 2007

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IPCC's Working Group I Summary Released

By Laura Edwards
Western Regional Climate Center

On February 2, the Intergovernmental Panel on Climate Change (IPCC) released their report from the first of three Working Groups: "Climate Change 2007: The Physical Basis". This document states that there is "very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming". The report goes on to state that most of the observed increase in globally averaged temperature during the last century "is very likely due to the increase in anthropogenic greenhouse gas concentrations". Over 2500 expert scientists reviewed the document which summarizes with confidence the burning of fossil fuels has led to the warming of our planet and the planet will continue to warm. What does this mean for California?

Figure 1. From Our Changing Climate: Assessing the Risks to California. Reduced mountain snowpack is one risk outlined in the report.

"Our Changing Climate: Assessing the Risks to California" was released last fall and utilizes the same information that went into formulating the IPCC report. Funded by the California Energy Commission and the California Environmental Protection Agency, over 75 scientists examined results from the latest climate change projections and assessed threats to the public health, economy and environment of California.

California's climate is projected to warm between 3 and 10 F over the next century. Several emission scenarios were examined to come up with the range in temperature change. Emission scenarios are formulated to estimate the amount of carbon dioxide, methane, and other greenhouse gases using projections of population, development, and policy. By 2034, all scenarios used in this study show an increase in temperature below 3 F. By 2099, all scenarios show an increase of 3 F and higher emission scenarios show an increase of between 6 and 10 F. No significant change in precipitation is projected for California by any of the emission scenarios.

Worsening air pollution, intense heat waves and wider ranges for infectious diseases were some of the public health issues examined in the report. Higher temperatures would increase the frequency, duration and intensity of air pollution episodes, increasing risks for those suffering from asthma and other respiratory diseases. More intense heat waves would raise the number of deaths due to dehydration, heat stroke, heart attack and other heat-related illnesses.

Projections indicate an alarming decrease of 70 to 90 percent in Sierra Nevada snowpack by the end of this century. This would dramatically impact the availability of water for urban and agricultural uses. It could also reduce the amount of power generated and affect winter recreation.

Figure 2. From Our Changing Climate: Assessing the Risks to California. This graphic shows potential impacts on California given 3 ranges of warmer temperatures as projected by climate models.

At risk would be California's $30 billion agriculture industry that provides half the country's fruits and vegetables. Increasing temperature is expected to affect wine grape quality, reduce chill hours needed by fruit and nut trees for proper bud setting, and stress dairy cows, thus reducing milk production. Threats to agriculture such as an expanding range of agricultural weeds and an increase in pests, may also be exacerbated.

The beauty of California is also threatened by climate change. An increased risk of wildfires and a decline in forest productivity in a warmer climate along with increasing coastal floods are likely to result in higher costs for preservation and protection.

Like the IPCC report, the California report acknowledges the significant impacts global warming will have and stresses the need to not only respond by reducing activities that increase emissions but to be prepared to cope with unavoidable climate change.

1. IPCC, 2007. Climate Change 2007: The Physical Basis, Summary for Policymakers.

2. CEC, 2006. Our Changing Climate: Assessing Risks to California.

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