Global warming

Less snow and more rain storms may be the wintertime trend for the northern Sierra Nevada in 30 to 50 years, causing increased erosion and sediment loading into Lake Tahoe, according to scientists.

A group of researchers Thursday issued the results of a two-year study on how global warming will effect the state of California. Temperatures from 2030 to 2050 likely will be 5 to 6 degrees higher in the winter, 1 to 2 in the summer. With the higher temperatures, an increase in winter precipitation is expected. Rather than snow, however, much of it could be rain.

That could mean more chance of flooding and more erosion, which is a contributing factor to Tahoe's declining clarity.

"Rain in the Sierra transports much higher concentrations of nutrients and pollutants than does snow," the report states. "A shift to more rain is likely to increase deposition of contaminants into relatively pristine mountain lakes, reducing clarity."

Chris Field, a scientist from the Carnegie Institution and lead author of the report, said the increased wintertime runoff likely will be a factor in Tahoe's declining clarity.

"Wintertime runoff will increase; runoff at the time of snowmelt will decrease," he said. "With that kind of event, flooding and landslides will happen more often."

More summertime storms also are possible, Field said, which tend to take particles from the atmosphere and deposit them into lakes such as Tahoe.

"Climate conditions can alter rain or wind-borne deposition of pollutants and nutrients, which acidify or cause excessive algal growth and murkiness in normally clear, nutrient-poor mountain lakes," the report states.

The top six feet of Tahoe acts as a reservoir, and the Upper Truckee River provides water to the Reno area. The change in precipitation trends, Field said, could affect Tahoe's and other alpine lake's effectiveness as reservoirs.

Field said global warming also could effect Tahoe's vegetation and wildlife. In general, plant and animal habitats likely will shift to higher-elevation areas with cooler temperatures. Large die off of plants and trees may be possible. Pests such as the bark beetle could be more prominent if the temperatures stress their hosts.

"Wherever you are, there will be a pressure for plants and animals that have been growing and living there in the past to shift to cooler areas," he said.

Field and several scientists from Stanford University, the University of California at Santa Barbara and the Lawrence Berkeley National Laboratory produced the report "Confronting Climate Change in California: Ecological Impacts on the Golden State."

"The real bottom line in the report is climate change is real," Field said. "We have increasingly good estimations of the rate of which climate change is coming."

However, Field said the report isn't supposed to be filled with "doom." It includes suggestions on how California - which has the seventh largest economy in the world and 20 percent of the United State's population - can do its part to avoid problems associated with global warming. One of the suggestions is something Tahoe governments already are doing - limiting the "footprint" of development, especially in environmentally sensitive areas.

"Limiting the area of human infrastructure can preserve habitat, maximize the size of habitat patches and avoid severing the connections among natural areas in the landscape," the report states. "Restoring degraded habitats can also be a vital complement to limiting the footprint of development."

Additionally, Californians can reduce their use of fossil fuels, especially in automobiles. While the state comprises 0.5 percent of the Earth's population, it consumes 2 percent of the fossil fuel, emitting more than 400 tons of carbon dioxide a year.

"Their individual actions as consumers can be globally significant," the scientists say. "Perhaps more important, however, is the fact that California has long served as a leader in attitudes, aspirations and innovative practices, including many that help to reduce emissions of greenhouse gases.

"As a consequence, today's Californians could become models for the nation and the world by encouraging and embracing the development of novel energy, transportation and land-use solutions to the problem of global climate change."

Other findings in the report include:

- Warmer, drier summers could cause an increase in hard-to-control wildfires.

- Decreased summer stream flows may intensify competition to meet the water needs of agriculture, industry and urban areas.

- Decreased summer runoff into San Francisco Bay could decrease the salinity of the water, possibly hurting the aquatic life there.

- Higher temperatures likely will warm the ocean, raising its level 8 to 12 inches by 2100, doubling or tripling the amount of change that has happened in the last 150 years. That could lead to intense storm surges and increased coastal erosion.

- El Nino years could increase; La Nina years could be stronger.