Climate and Weather: 12 Things You Need to KnowAssociation News
By Michael Sullivan, Chairman, General Plan Committee
Last year at this time, you could often hear, “Look Mom, another snow day.” This year it’s, “Look Mom, no snow.”
With all we hear and read, it’s easy to assume that the dreaded “climate change” is already here and our beloved winter sports are finished. But before you draw that conclusion, let’s look at the facts and what we can do to preserve the sports we love.
As National Geographic points out, “When scientists talk about weather, they’re referring to day-to-day changes and when they discuss changes to the Earth’s climate, they’re referring to changes over time”. The time scales for weather are days, weeks and years; the time scales for climate are decades, centuries and millennia.
The changes we have seen between last year and this are changes caused by weather, so let’s address that first.
WHAT IS WEATHER?
Day-to-day weather involves the complex interaction between the sun and the earth, gravity and inertia, heat and cold, and the three states of matter: solid, liquid and gas. Using supercomputer generated models, scientists are developing an understanding of these interactions; however, the complexity is, so far, beyond our ability to make exact forecasts.
HEATING AND COOLING
Weather begins with the sun shining on Planet Earth and warming the surface. Because the air of our atmosphere is in contact with the surface, it is heated as well. Because hot air expands, it becomes lighter and rises. This movement of air is called convection and it is lucky for us that this happens for if there were no convection, the surface of the Earth would be over 300ºF and we would not survive.
[caption id="attachment_14155" align="alignnone" width="300"] Figure 1. https://en.wikipedia.org/wiki/Hadley_cell#/media/File:Earth_Global_Circulation_-_en.svg[/caption]
Hot air rises over the equator and descends when it cools. There are six global convection cells, shown in Figure 1, of rising and cooling air. Where they intersect, winds are created that circle the globe. These are the jet streams.
[caption id="attachment_14144" align="alignnone" width="234"] Figure 2. https://commons.wikimedia.org/w/index.php?curid=3737997[/caption]
THE JET STREAM
The North Polar Jet Stream, shown in Figure 2, is a stream of air that is much colder than its surroundings. This air current moves cold air from West to East at velocities that can exceed 200 miles per hour. The Polar Jet Stream in the Northern Hemisphere is often at the latitude of Canada but can vary considerably and, as we have seen this year, can send polar air as far south as Florida. When it delivers its effect to the West Coast of North America, we have a nice cold, snowy winter. When it moves eastward, we have a cold but dry winter. The polar jet stream is affected by ocean currents.
AS THE WORLD TURNS
As hot air rises, colder surrounding air is drawn in to replace it, causing wind. Because the Earth is rotating, the air over the equator is moving faster than the air over the poles. At the equator, the surface moves at almost 1,000 miles an hour. At our latitude, it is closer to 700 miles an hour and at the North Pole it is virtually zero. This movement of the earth causes the rising air to swirl in a counter-clockwise direction in the Northern Hemisphere. You see this swirling when you look at satellite pictures of hurricanes. This is called the Coriolis Effect.
As hot air rises and gets farther from the surface, it cools and when it does, the gaseous water vapor contained in the air condenses out as liquid water droplets in the form of clouds. If it rises high enough, these water droplets can even freeze into ice. The wispy cirrus clouds we see (sometimes called Mare’s Tails) are ice clouds 5 miles above the ground.
[caption id="attachment_14145" align="alignnone" width="300"] Figure 3. From Chapter 15 of “The American Practical Navigator”, originally by Nathaniel Bowditch, published by the National Imagery and Mapping Agency, Bethesda, MD.[/caption]
The heating of the Earth’s surface is not uniform. When the sun is directly overhead, the surface is heated more than when it is at an angle. Because the Earth is tilted on its axis, the part that is directly under the sun changes throughout the year as the Earth moves around the sun. On March 21 and September 21, the sun is directly over the Equator and that will be the hottest part of the planet. On June 21, the sun is directly over the Tropic of Cancer, which is at 23.4º North latitude or about 1,600 miles north of the equator. This is approximately the latitude of the Caribbean. This change in sun angle gives us our seasons, as illustrated in Figure 3.
In addition to the tilt of the Earth, the heating of the surface depends on whether that surface is a solid such as land or a liquid such as the oceans. Land heats up rapidly during the daytime and cools just as rapidly at night, whereas the oceans respond to the sun’s heat very slowly and in doing so, create their own convection currents like the Gulf Stream in the Atlantic and the Humboldt Current in the South Pacific.
In addition to these ocean currents, there are also periodic changes or oscillations in ocean temperature. The two that have a dramatic impact on our weather are the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Peruvian fishermen in the 1800’s noted that every seven to ten years, their catch declined at Christmas time and they named this effect after the Christ Child or El Niño. As these masses of warm water move closer or farther from North America they change the amount of moisture picked up by the air above and thus the amount of precipitation we receive in the Sierra Nevada Mountains.
Should we be concerned that winter is over because of climate change?
[caption id="attachment_14146" align="alignnone" width="300"] Figure 4. https://data.giss.nasa.gov/gistemp/graphs/graph_data/Global_Mean_Estimates_based_on_Land_and_Ocean_Data/graph.png[/caption]
GLOBAL CLIMATE CHANGE
At the same time that all this weather is happening, gradual changes are taking place over the entire planet. Oscillations of temperature have occurred since the planet solidified. The polar ice caps have grown and shrunk as a result and accompanying precipitation variations have changed jungles into deserts and vice versa. Typically, these changes occur over hundreds or thousands of years. Right now, the Earth is in a warming cycle, as shown in Figure 4, although the warming is greater over land than water. International climate studies indicate that the earth has warmed about 1.53ºF from 1880 to today and the temperature increase is accelerating. Many scientists believe that the burning of fossil fuels that began with the age of industrialization causes some of this effect by adding heat-trapping carbon dioxide to the atmosphere. As the planet warms, the interrelated systems that make up our weather become unstable, causing weather-related events such as hurricanes, tornadoes and wildfires to become more severe. Also, precipitation patterns change, producing prolonged droughts where previously there was sufficient rainfall.
It should be noted that although over 97% of climate scientists agree with the view that the planet is warming, there is a group with a contrarian view.
[caption id="attachment_14147" align="alignnone" width="300"] Figure 5. Source: wikipedia[/caption]
How fast are these mega changes happening and will they affect our lifestyle in Tahoe? The answer is clearly yes, eventually. Different models of long-term climate predict differing results, as you can see in Figure 5. All of the measurements indicate that this warming trend will result in almost no snow in the mountains by the year 2100. From now until then, droughts and unpredictable weather patterns will be the new normal.
One implication of this warming trend is that precipitation amounts will diminish in North America, thus further reducing snowfall. Because of this, ski resorts around the country that have sufficient water supplies are investing large sums in snowmaking to insure the continuation of winter sports activities for most of the rest of this century. Fortunately for Tahoe Donner, we have abundant water so that, if we wish, we can make the investment to provide winter sports and recreation for our children and grandchildren.
Your Tahoe Donner General Plan Committee regularly researches topics like these in our volunteer work to analyze, evaluate and recommend to the Board of Directors those projects that will benefit members. Your input is always welcome, at the GPC meeting at 3:00 pm on the first non-holiday Monday of each month at the Northwoods Clubhouse, or via email to firstname.lastname@example.org.