Bob Ryan on Global Warming, Part 4
Is our climate changing?
By BOB RYAN
Updated 8:33 AM EST, Mon, Mar 9, 2009
Cleveland volcano in Aleutian Islands photographed from the International Space Station in May 2006.
Sunspot number over the past 11,000 years from data by Solanki, S.K. et. al. NOAA
A general El Nino-La Nina (ENSO) index. Red indicates El Nino or warm phase in the tropical Pacific and blue the cool or La Nina phase of the El Nino Southern Oscillation.
During the El Nino, or warm phase of ENSO, warm waters in the Pacific release heat and moisture into the atmosphere and the global temperatures tend to be higher than in La Nina years.
As you can see above, there are a number of natural (as opposed to man-made) factors that influence our skies, (remember the beautiful sunsets after Mount Pinatubo erupted?) our weather and our climate. Of course, our Sun is THE big guy on the block, so to speak. For centuries it was believed that the Sun never changed, never varied ... that it was a constant.
Courtesy NASA and University of Colorado
Fortunately, our Sun is not a true variable star (http://www.aavso.org/). However, as you can see in the sunspot record the sun does have its own “climate,” if you will, the 11-year sunspot cycle, which is now ending at a minimum and should lead to increasing numbers of sunspots and a slight increase in the total solar irradiance, which instruments can now accurately measure.
If the Sun were to go into a very “quiet” phase as it has done in the past in the 1600sduring what is called “The Maunder Minimum”, it could lead to a cooling of the Earth and climate, like it did from the mid-1600s to the early 1700s called the “Little Ice Age.”
Sunspot number was very low and total solar irradiance decreased for more than 50 years and Europe experienced very cold winters as captured by Dutch masters:
"Hunters in the Snow" by the Flemish painter Pieter Bruegel the Elder (1525-1569). It was completed in February 1565.
But most solar scientists expect the Sun to shortly begin to show more sunspots and not go into an unexpected long “quiet” time, as happened about 500 years ago.
Most studies show that natural variations in our Sun during over-normal solar cycles may affect the average temperature of our atmosphere, contributing a warming and cooling effect of about +/- 0.2° F. These sun-caused oscillations, or periodic changes of the average temperature of the atmosphere, occur with other natural causes and are what scientists call a natural “forcing” or natural driver of the atmosphere-oceans system, as shown below from a wonderful article on the Sun-Earth climate connections.
Courtesy Physics Today “Living With a Variable Sun” Judith Lean Physics Today, Volume 58, Issue 6, pp. 32-38 (2005).
Click here to read the complete article.
As if things weren’t complicated enough, volcanoes and volcanic eruptions have played a role in our climate. Volcanic eruptions can eject millions of tons of material into the air and even into the stratosphere and, for a time, form a thin umbrella in the atmosphere and decrease the amount of sunlight and solar energy reaching the ground.
The eruption of Mount Pinatubo in the Philippines in 1991 ejected about 20 million tons of SO2 into the air, which formed tiny droplets or aerosols of sulfuric acid that spread around the world in the stratosphere and reduced the amount of sunlight by about 10 percent and decreased the average surface temperature of Earth about 1° F. in some areas the following two years.
Interestingly, some studies done at the UK Meteorological Office Hadley Centre show the effects of the Mount Pinatubo eruption on climate forecasts.
This also shows that incorporating current data can be a significant advantage in rather short-term (10-year) climate forecasts. Volcano eruptions can’t be forecast tens of years ahead, but certainly such eruptions as Pinatubo do have a dramatic short-term effect on global temperatures.
So there are many “natural” factors that have an effect on our climate and the global temperature and precipitation patterns, but as shown in the work at NCAR, to understand the influence of the natural and human (anthropogenic) factors, the influence of human factors, mainly increasing CO2, has been reproducible as shown in the results below.
This graph, constructed from a global climate model, shows that natural forcing (volcanoes and solar) cannot explain the observed global temperature variations over the 20th century. However, when anthropogenic effects are included, the model reproduces the observations quite well
Courtesy NCAR
The average global temperature is variable because many natural and man-made factors affect our climate and weather. But why hasn’t the now 35 percent increase of carbon dioxide in the atmosphere made our climate much warmer, as some thought would happen years ago? Back to some observations thanks to wonderful NASA satellites. I know ... we’re almost finished.
Until next time, Scarlett.
First Published: Feb 25, 2009 3:13 PM EST
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