I spoke with Rick London, CEO of United Way of San Luis Obispo County, last week about Earth Day and the subject of giant sequoia trees, also known as Sierra redwoods, in Sequoia National Park was brought up.

They are the largest trees on Earth and can live for over 3,500 years. Few life experiences can match standing in one of these redwood groves.

When they die, it is often indirectly because of root weakening. Rick told me about the one massive tree that toppled over in the park in 1998. That year, one of the most potent El Niño events ever seen produced near or record amounts of snow and rain throughout California.

The memory of that giant sequoia on the ground left a lifelong impact on him and has increased his desire to preserve the environment. So much so, he illustrated a story about it that can be seen at www.unitedwayslo.org/cpr-squared

These redwoods have witnessed a lot of climate history, but never at a pace as the last the 50 years, and here is why.

The first Earth Day was celebrated on April 22, 1970, and during that time, the carbon dioxide (CO2) level in the atmosphere was 320 parts per million (ppm). This month, it was nearly 419 ppm at the Mauna Loa Observatory in Hawaii.

This unprecedented increase in CO2 is mostly from burning fossil fuels.

"Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over the span of many millions of years; we are returning that carbon to the atmosphere in just a few hundred years," according to the State of the Climate in 2019 from NOAA and the American Meteorological Society.

As Adm. David Titley will tell you, "To compare that to something readers may be familiar with, a blood alcohol level of 0.04%, or 400 ppm, puts a partygoer well on the way to intoxication. If we increase our blood alcohol to 800 ppm or 0.08%, we are legally impaired."

CO2 is a greenhouse gas, which functions like the glass in a greenhouse, allowing the sun's light to pass through, but taping the infrared radiation (heat) near the Earth's surface.

Natural climate change occurs over thousands of years due to variations in Earth's orbital cycles around the sun. Eccentricity, the deviation of our planet's orbit from a perfect circle, is a 100,000-year cycle. Earth's axial tilt varies over a 41,000-year process, and Earth's precession (wobble) on its axis occurs over a 26,000-year progression.

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Unlike natural climate change that happens over the millennia, human-induced global warming is occurring over mere decades.

Since 1970, the average U.S. temperature has warmed by 2.4-degree F according to Climate Central, an independent group of scientists and communicators who research and report the facts about our changing climate.

Temperature data from their website www.climatecentral.org indicates that Santa Maria Airport has seen a 3-degree F increase in average temperatures since 1970. South of the Central Coast, Los Angeles has warmed by 0.5 F, while San Francisco is 2.8 F hotter. Reno, Nevada, saw the most significant increase in the United States at 7.6 degrees, followed by Las Vegas at 5.8 degrees.

Rising air temperatures is a problem, but the world's oceans may pose even a greater challenge. You see, the oceans are absorbing 93.4 percent of this heat said Dr. Josh Willis of the Jet Propulsion Laboratory (JPL). These rising ocean temperatures are causing 268 ± 14 billion metric tons of ice per year to melt from the Greenland.

Dr. Willis and the NASA Oceans Melting Greenland (OMG) team have flown out of Greenland's airfields for years. They have deployed numerous bathythermograph (BT) buoys that measure seawater temperatures from a recently refurbished Douglas DC-3 cargo plane around Greenland's glaciers.

They have recorded a warming of Atlantic seawater in contact with these glaciers, resulting in more significant melting.

So far, the loss of ice has resulted in nearly half an inch of sea-level increase worldwide. If all the ice were to melt from Greenland, it would produce a 25-foot rise in sea level. Dr. Willis told me that about 40% of the recent sea-level increase is due to thermal expansion of the ocean, 30% from land glaciers, and 30% from the melting of the ice sheets in Greenland and Antarctica.

In the future, the rate of sea-level rise will increase, with the main contributor being the melting of the ice sheets. By 2100, most climate scientists are expecting about a 47-inch increase in sea level.

PG&E exceeded California's Renewables Portfolio Standard (RPS) goal requiring energy providers to deliver 33% renewable energy by the end of 2020. PG&E estimates that it delivered over 35% from specified eligible renewable resources to its customers last year.

Overall, more than 88% of the electricity PG&E delivered to its customers last year came from greenhouse gas (GHG)-free resources, including eligible-renewable, nuclear and large hydroelectric energy. To learn more, visit www.pgecurrents.com.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.