Climate Change

Lecture 6

March 4, 2010

Climate Change Assignment

• Due next Thursday, March 11

• 2-3 paper on climate change and your assigned greenhouse gas

• Must use at least 3 sources and include Works Cited page

• Be prepared to discuss climate change in class

• More detailed description up on website

Weather vs. Climate• The difference between weather and climate

is a measure of time• Weather is the state of the atmosphere, land,

and ocean conditions on a day to day basis. • Most people think of weather in terms of

temperature, humidity, precipitation, cloudiness, visibility, wind, and atmospheric pressure

• Climate is the average weather in a location over a long period of time (months, years, decades, etc)

• Climate is what you expect, like a very hot summer. Weather is what you get, like a hot day with thunderstorms. 

Weather and Climate

• Both weather and climate are influenced by a variety of factors such as…

• Astronomy (Earth’s tilt, rotation, distance from sun, and solar activity), terrain, location, humans

• The Earth’s climate undergoes many natural changes and cycles

Why study climate?• Studying climate and a changing climate is

important because it will affect people around the world

• Rising global temperatures are expected to raise sea levels and change precipitation and other local climate conditions.

• Changing regional climate could alter forests, crop yields, and water supplies. It could also affect human health, animals, and many types of ecosystems.

Global Climate Controls

• Earth’s orbit and tilt

• Land/sea distribution

• Sun’s strength (long-term)

• Earth’s albedo

• ENSO

• Greenhouse Gas Effect

Earth’s Orbit and Tilt

• Orbit (Eccentricity)– How close is Earth’s orbit

to circular?– Governs max. and min.

distance from the sun– Orbit naturally fluctuates

over 100s of thousands of years

• Tilt (Obliquity)– Increased tilt increases

seasonality– Tilt naturally fluctuates over

tens of thousands of years

Land/Sea Distribution• Continents drift and shift

over time (plate tectonics)

• Pangaea: supercontinent that existed about 250 million years ago

• Affects ocean currents, wind patterns, etc

• Continents are still moving today and will continue to shift

Strength of the Sun• Sun goes through natural

cycles of increasing and decreasing strength– These cycles are tens

of thousands of years long

• Sunspots follow a 11 year cycle (affects incoming radiation)

• More output from sun warmer Earth

http://science.howstuffworks.com/sun.htm/printable

Albedo• The Earth actually reflects

much of the sunlight it receives

• Light that in reflected back to space does not warm the Earth

• The percent of sunlight the earth reflects is called the albedo

• Changing this albedo changes the amount of energy from the sun that is absorbed by the Earth! (thus changing the climate)

What changes the albedo?

• Increase in snow and ice cover

• Increase in areas covered by sand

• Deforestation

• Increased cloud coverage and thickness

• Volcanic eruptions (releases ash and small particles into atmosphere)

• Changes in land cover (vegetation vs asphalt, etc)

ENSO

• El Niño Southern Oscillation

• Defined together as a periodic change in the atmosphere and ocean of the tropical Pacific region

• El Niño and La Niña are the oceanic aspects of the phenomenon and the Southern Oscillation is the atmosphere aspect

ENSO

• El Niño and La Niña events are defined as warming or cooling of surface waters of the tropical central and eastern Pacific Ocean

• Southern Oscillation is defined by the sign of the pressure difference between Tahiti and Darwin, Australia

• The oscillation does not have a specific period, but occurs every three to eight years

ENSO Classification

• A warming or cooling of at least 0.5 C (0.9°F) averaged over the east-central tropical Pacific Ocean

• When this temperature anomaly persists for five months or longer, it is called an El Niño or La Niña episode

El Niño• El Niño occurs during a

time of suppressed trade winds (winds moving from the east to the west) at the equator

• Causes a pool of warm water to collect in the eastern Pacific near S. America (water there is normally cool)

• Changes global wind patterns and temperature, altering weather on global scale

Moderate to Strong El Niño occurring now

Greenhouse Effect

• The atmosphere itself absorbs almost none of the sun’s incoming radiation

• The Earth’s surface absorbs part of the sun’s energy and warms

• Greenhouse gases in the atmosphere act to trap in some of the longwave radiation leaving the Earth.

• Without greenhouse gases, ALL of the energy radiated by the surface would escape to space

Greenhouse Effect• The radiative equilibrium temperature of

the earth with no atmosphere is 0°F

➔ Adding greenhouse gases increased the radiative equilibrium temperature to 59°F

• Main greenhouse gases: Carbon dioxide, water vapor, methane

• More greenhouse gases = more energy kept at the Earth’s surface = warmer average temperatures

• We MUST have greenhouse gases in order to survive but we don’t want too many because we will overheat

This is a scientific fact!

Climate Change

• Climate change is a change in the statistical distribution of weather over periods of times that range from decades to millions of year

• Can happen in a variety of ways and variety of places (specific region or whole Earth)

• One example that is the topic of concern right now is how the climate for the entire globe has become warmer.

• A skeptic to the fact of global warming might say “What about the temperature record in the interior of Antarctica where there is a cooling trend?”

History of Climate Science

• Most people think global warming is a new theory - it is not!

• Svante Arrhenius first theorized that surface temperatures would increase with increasing CO2 concentrations in the 1890s

Early 1900’s

• Scientists ignored the theory, saying the ocean will “suck up” all of the CO2 we emit

• The ocean has sucked up HALF of all human CO2 emissions since the industrial revolution, but is becoming saturated

Also: http://data.giss.nasa.gov/gistemp/graphs/

Global Warming EvidenceGlobal Warming Evidence

http://www.globalwarmingart.com/wiki/Image:2000_Year_Temperature_Comparison_png

More Observations Has Led To Better Knowledge

Observations of CO2 concentrations

• Increase in greenhouse gases from 1700 to today results in 2.43 W/m2 more energy at the surface

CO2 accounts for 60% of the increase → 1.46 W/m2

Recent Global Warming• CO2 has increased 25% in the last century and

solar radiation incident on earth has slightly increased

• Why has the rise in global temperatures been relatively small?→ Reflective sulfate aerosols– Major volcanic eruptions between 1880 -1920 and

1960-1991– Sulfur particles into the stratosphere

→ lower the albedo → cooling effect

Cooling effect (increased albedo)+ Warming effect (increased greenhouse gases)= Small net warming

Climate ModelingThe last 150 years

Projected Global Warming

• Modeling the last 150 years, we have a good idea of – Greenhouse gas emissions by humans– Vegetation changes

• Future projections of climate change needs estimations of – Greenhouse gas emissions– Population changes– New technologies– Vegetation

Intergovernmental Panel on Climate Change

• IPCC established in 1988 by the World Meteorological Organization and UN

• Publishes special reports on topics relevant to climate change

• “Most of the observed increase in global average temperatures since the mid-20th century is very likely (90% likelihood) due to the observed increase in anthropogenic GHG concentrations.”

• “The probability that this is caused by natural climatic processes alone is less than 5%.”- IPCC 4th Assessment Report

Projected Global Warming• A2 → Slow economic/technological growth, high

population growth• A1B → Rapid economic/technological growth,

population peaks midcentury• B1 → Medium population/economic growth,

emphasizing local solutions and sustainability

How will a potential global average warming affect climate?

• Land areas are going to warm more than ocean areas– As snow-covered tundra melts, boreal forests will

absorb 3 times as much solar energy

• More frequent intense precipitation events and flooding– Warmer air temperatures hold more water vapor

• Polar front and jet will shift northward– Subtropical regions will be warmer and drier– Shift in mid-latitude weather systems northward

• A warmer planet will see a rise in sea level.– Warmer water is “thicker”– Melting ice caps

Supporters of Global Warming and its Connection to Supporters of Global Warming and its Connection to Increased Amounts of Greenhouse Gases say… Increased Amounts of Greenhouse Gases say…

• The rise in CO2 and other greenhouse gases is definitely anthropogenic

• Historical temperature records show an increase of 0.4-0.8oC in the last 100 years

• This has been an unusually warm period when comparing it to the last 1000 years

• CO2 is a first order forcing of climate change

• There will be long term ramifications if we don’t do something now!

Opponents of Global Warming and its Connection to Opponents of Global Warming and its Connection to Greenhouse Gases Say…Greenhouse Gases Say…

• IPCC, and other atmospheric scientists, draw most of their conclusions from climate models. These models have major flaws with cloud physics, and don’t necessarily include every kind of climate forcing!

• On that note, climate models don’t even include all climate feedbacks (ice-albedo feedback, etc.)

•Just because we’ve observed the temperature to rise around the start of the Industrial Revolution doesn’t necessary mean that increased fossil fuel use has caused the temperatures to increase

•The observational records are flawed

• The Earth has observed many climatic shifts of its history, some of which aren’t that well understood