Wednesday, August 21, 2019

Listen to the Trees

published in the Pacifica Tribune August 20, 2019

What’s Natural? 

Listen to the Trees!

This summer I taught a class on the Natural History of the Sierra Nevada for San Francisco State University’s Sierra Nevada Field Campus. The first day we taught students how to identify the trees. Once students know their trees, they can easily see how tree species vary with elevation, temperature, moisture, and snow pack. They can see which species colonize open sunny areas and which trees need shade before they can invade. Old time naturalists used trees to identify “life-zones” where different species of mammals, birds, insects and other plants can be found. Furthermore, when you listen to the trees, you can see change.

The class explored forests along the North Yuba River. Free from politics, trees tell us about changes in fire frequency, logging, climate change and ecosystem resilience. Photographs taken during the late 1800s during California’s gold rush days, revealed the total devastation of local forests. Gold miners needed wood for heating and cooking, for their metal forges, and for timbers to reinforce their mines. They needed wood to build flume boxes that altered river courses to expose riverbeds. Flume boxes also carried water from high to low elevations where giant water cannons completely washed away hillsides in their search for gold.

Deforested mountains - Downieville, CA late 1800s

Still, by comparing catastrophic photos of forests during the gold miners’ days to our current forest conditions, I was filled with optimism. The forests had totally recovered and again are quite dense. So dense, that local inhabitants fear there’s too much fuel on the forest floor that could feed catastrophic fires. Nevertheless, the lush re-growth is testimony to our forest’s amazing resilience. 

We counted tree rings and determined a majority of trees were no more than 170 years old. Those trees began their lives shortly after the gold miners had cut down all their older relatives. Occasionally we found a few larger trees, 300 years or older, that fortuitously avoided the miners’ ravenous saw blades.

Scientists determine the natural frequency of fires by reading tree rings and fire scars. Low elevation trees like Ponderosa Pines naturally endured wildfires about every 25 years. At higher elevations, where temperatures are colder and the snow pack lingers, fire scars suggest wildfires naturally happen about every 100 years. In contrast to media hype, fire scars in living and fossil trees suggest wildfires were far more common during the cool Little Ice Age.

Tree stumps tell us that trees once bordered Arctic shores 9000 years ago. Since then, cooler temperatures have pushed trees to lower latitudes and warmer elevations. Hikers in the Sierra Nevada often encounter dead trees several hundred feet above our current tree line. Accordingly, researchers determined that for the last 3 thousand years, tree line was mostly higher than today because temperatures were much warmer. However, during the Little Ice Age, between 1300 AD and 1850 AD, it got so cold, tree line dropped and tree seedlings in the Ural Mountains couldn’t germinate for hundreds of years. Ancient tree lines suggest if temperatures increase over the next century, it will not be a crisis. Trees will simply reclaim their former habitats. 

Trees reveal past rainfall patterns. California’s Blue Oaks are very sensitive to changes in precipitation. In drought years they generate narrow rings contrasting with wider rings during wet years. A recent tree ring study of Blue Oaks finds no rainfall trend over the past 700 years, but it suggests Californians can expect extreme droughts and extreme rainfall 3 to 4 times a century. More concerning, tree stumps at the bottom of Lake Tahoe dating back 6000 years ago, suggest Californians can naturally expect far more extreme droughts than living humans have yet to experience. 

Trees tell us how climate has changed. Fossil trees indicate Antarctica once experienced subtropical temperatures 40 million years ago. Similarly, trees tell us about recent temperature changes. Tree rings have correlated accurately with instrumental temperatures for over 100 years. However, since the 1960s, tree ring temperatures suggest a much cooler global climate in contrast to thermometers and models. 

Tree ring temperatures 

Tree rings indicate the warmest decades of the 20thcentury were the 1930s and 40s, and temperatures have yet to surpass those decades. This divergence between thermometers and trees is best explained by the fact that instrumental temperatures are biased upwards when taken at hot airports or in areas recently suffering from growing urban heat island effects. In contrast, trees measure temperatures in natural habitat.

There are too many fear mongering politicians pushing an “existential climate crisis”. I find the climate history told by the trees far more trustworthy, and the trees are whispering there is no crisis. 

Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism

Wednesday, August 7, 2019

Ten Causes of Warming: The Layperson’s Checklist

published August 7, 2019 

What’s Natural? 

Ten Causes of Warming: The Layperson’s Checklist

All temperatures are not created equally. Rising temperatures have many causes. Good science demands we explore alternative hypotheses before reaching any conclusions. Below is a list of common causes of warming trends and heat events that everyone should consider in addition to any possible increased greenhouse effect.

1.     Heat trapping surfaces: Asphalt and cement not only heat up much faster than natural habitat during the day, those materials hold the heat longer, increasing temperatures at weather stations situated near buildings and near asphalt. More asphalt, more warming, more record temperatures.

2.     Loss of Vegetation: During the summer the temperature of a dry dirt road can be 60°F higher at noon, than ground shaded by trees. That’s why our pets instinctively seek the shade. Plants also bring moisture from below the ground that cools the air by evaporative cooling. Increasing deforestation or lost vegetation due to landscape changes cause regional warming trends.

3.     Transport of heat: Natural climate oscillations alter air and ocean circulation patterns that can drive more heat from the tropics towards the poles. Europe’s recent heat wave was largely caused by air heated over the baking Sahara Desert and then driven into Europe. Similarly, the latest research finds variations in Arctic sea ice has been dominated by transport of warm Atlantic water heated in the tropics and transported northward via the Gulf Stream.

4.     Less cloud cover: Recent research suggests a trend of less cloud cover resulted in increased solar heating of land and oceans. The added solar energy normally reflected by clouds was 2 times greater than what’s believed to be added by increasing carbon dioxide. Two decades of declining cloud cover was similarly shown to cause Greenland’s rapid ice melt between 1995 and 2012.

5.     Less Cooling: Windy conditions cool the oceans. The unusually warm ocean conditions that occurred in the northwestern Pacific Ocean, known as the Blob, were caused by decreased winds that reduced normal cooling. 

6.    Suppressed Convection: Surface temperatures are cooled by rising convection currents that carry away the heat. Roll up the windows of your car and immediately the temperature rises simply because convection is prevented. Suppressed convection is the reason temperatures are warmer inside agricultural greenhouses. Weather-people predict a heat wave when they see a looming dome of high pressure that will suppress cooling convection.

7.     Drier conditions: It takes 5 times more energy to heat water 1 degree than it does to heat sand. Furthermore, it takes 500 times more energy to evaporate water than it does to raise water one degree. Without evaporation to consume the heat, most extreme temperature events are associated with dry conditions. The trend in lost wetlands increases temperatures.  

8.     Ventilating stored heat: Oceanographers from Harvard and MIT have suggested heat stored in the deep oceans thousands of years ago, when temperatures were warmer than today, is still ventilating. Likewise, El Niños ventilate previously stored heat. Similarly, Arctic temperatures rose after a change in wind direction blew thick insulating ice out of the Arctic allowing subsurface heat to ventilate.

9.     Descending winds: For every 1000 feet of elevation that an air mass descends, its temperature rises over 5°F. California’s hot Santa Anna and Diablo winds can raise downslope temperatures 25°F in a matter of minutes. Descending air in a high-pressure dome suppresses convection causing heat waves. Despite temperatures far below freezing, bouts of descending winds from Antarctic’s peaks rapidly heat the ice and generate melt ponds.

10.  Misleading Averaging: The average temperature is calculated by adding the maximum and minimum daily temperatures and dividing by 2. Due to heat trapping surfaces, higher minimum temperatures cause the average temperature to rise even when maximum temperatures have not increased or sometimes cooled.

Good stewards of the environment should never mindlessly blame rising CO2concentrations for a heat wave or a warming trend unless all the other warming dynamics are considered. Restoring a wetland or planting trees might be the best option to lower regional temperatures.

Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism. He writes regular column for Battle Born Media newspapers -- the Pacifica Tribune, the Novato Advance, the Sausalito Marin Scope, the Mill Valley Herald, the Twin Cities (Larkspur and Corte Madera) Times, the San Rafael News Pointer and the Ross Valley Herald.