Lecture 3.2: What’s this “Greenhouse Effect” Thing anyway?

Today - Climate variation Changes in climate –Short period changes –Long term changes

Climate The average of the day-to-day weather over a long period of time at a specific place. The “normals” reported on television are really just climatological averages! Different parts of the world have different climates

Climate Variability Climate can change over time. There were once Glaciers over Britain and before that shallow tropical seas. But we are really interested in a more short-term climate change. A change that can be observed over a few years, or at least in our lifetime.

Short-term Climate Variability ¶Changes in the solar output.  The solar constant really isn’t.  Between 1981 to 1986, the solar output was measured to decrease by 0.018% per year.  The total reduction was almost 0.1% in six years.  Had this trend continued for another six years, the effects of the reduction in solar output may have had a noticeable effect on the global climate.

Changes in the solar output.

Short-term Climate Variability ·Changes in the number of sunspots.  Sunspots are relatively large dark spots that appear on the surface of the sun.  The temperature of the core of the sunspot is usually 4000 K compared to the 5800 K normal temperature of the surrounding solar surface.  Sunspot numbers tend to fluctuate in an 11 year cycle (22 years if magnetic fluctuations are included).

Sunspots

Short-term Climate Variability  There have been noted correspondence between sunspot number minima and colder temperatures on earth.  Between 1645 and 1715 there was a period of few sunspots. This is called the Maunder Minimum.  The Maunder Minimum corresponds to the “little ice age” where the average global temperature was estimated to be about 0.5 o C cooler.

Maunder Minimum

Changes in the solar output.

Short-term Climate Variability ¸Volcanoes  Large volcanic eruptions can have an impact on the climate of a region.  Particles are ejected into the atmosphere that can alter the amount of radiation received at the surface.  Sulfur compounds in ejected material can create sulfuric acid (H 2 SO 4 ).  This sulfuric acid absorbs solar radiation and increases the albedo.

Short-term Climate Variability A year after the eruption of Tambura, New England experienced the “year without a summer.” Heavy snow in June Frost in July and August June mean temperatures were 3.5 o C below normal August temperatures were 1-2 o C below normal Cold weather was experienced in England and Europe A year after the eruption of Pinatubo, the mean global air temperature dropped by almost 0.5 o C compared to the previous 9-year average.

Mt. Pinatubo

Short-term Climate Variability ¹“Greenhouse” Gases  Carbon Dioxide, Methane, Water Vapor, Nitrous Oxide, CFC’s  Increase CO 2 (and others) and increase the temperature of the earth’s surface  Do feedback mechanisms cancel this effect?

Regional climates Continental areas have extremes Coastal areas tend to be more moderate (temperate)

Water surfaces Water is dark and absorbs a lot of heat (except when the sun is low in the sky) Water surfaces stay cool because –When hot a lot of evaporation takes place –Water is a fluid and can mix within itself, therefore energy can be distributed quickly throughout the body of water (compared to soil/rock where heat is conducted slowly)

Is that why oceans are important in climate? As well as this water has a high heat capacity – it can hold a lot of energy and transport it around the planet because it is a fluid And it takes longer to heat up and cool down than rock –It stays relatively warm through winter and cool through summer –Coastal areas have less variation in temperature than inland regions

Summary How energy reaches the earth How it gets into the atmosphere How it is transported vertically within the atmosphere How these transport processes affect the climate.

Homework Read Chapter 2 of Ahrens Answer Questions for Thought numbers 4 & 11 Due Monday 15 th September (start of class)