Climate Change

• Most solar energy is in the form of shortwave radiation (e.g. light, uv rays)

• Earth absorbs this energy and re-emits as longwave radiation (infra-red, “heat”)

• Greenhouse gases (CO2, CH4 H2O) in the atmosphere absorb infrared radiation

• This natural process allows the Earth to maintain an average yearly temperature of about 150 C (600 F).

Climate change in the geologic past

• Early Precambrian Time (4-2.7 bya)– Sun was 20-30% fainter,

delivered less energy

– Effect offset by large greenhouse effect of Earth’s early atmosphere, largely composed of CO2, and H2O.

• Late Precambrian to Permian (2.7 bya to 250 mya)– Severe ice ages occurred at

least five times in this period

Climate change in the geologic past

• Mesozoic to Present– Climate mostly warmer than

today

– Most recent ice ages occurred over the last 2 million years

– Some scientists think the last 10,000 represent an interglacial warming episode and the ice will return

– Recent records show mean temperature increase from the late 1800s

“Recent” Climate change data from the Summit Ice Core.

Fig. 21-4, p.503

Fig. 21-5, p.504

Measuring recent climate change

• Historical records – accounts recorded as records, or in stories– Vikings’ tales of the Little Ice Age (1450-1850)– Wine harvest records– Landscape paintings, other historical &

archeological accountings chronicle changes over the span of human history

Climate Data from Historical Records

Measuring climate change

• Tree rings – growth rings of trees hold climate information

• Plant pollen – the pollen record records what was able to grow, which is linked to temperature and precipitation– i.e; 10,500 years ago pines replaced spruce in

what is now northern Michigan, indicating warmer temperatures.

Measuring climate change

• Oxygen isotopes in glacial ice– 18O & 16O (common isotope) both occur– 16O evaporates more readily (lighter)– Ice from Greenland and Antarctica show a

record back >100,000 yrs

• Glacial evidence – till, tillites, striations all give information on climate at that time– 14C dating of organic material preserved in till

Comparing oxygen isotope analysis with temperature in coral

• This figure shows a δ O18 ratios from a coral core. This record is plotted against variations from average annual sea surface temperature (SST) rainfall, and coral growth in order to observe how well these corals have recorded recent climate variability.

• Red shows higher than average SST/ rainfall/negative δ O18 (expected for warmer temperatures)/more coral growth.

Figure courtesy of Dr. Julie Cole, University of Colorado.

Fig. 21-6, p.505

“Recent” Climate change data from the Summit Ice Core.

Measuring climate change

• Plankton and isotopes in ocean sediment– Shells and other “hard parts” preserved in marine

rocks / muds give two lines of information• What was alive at the time gives climate information• 16/18O ratios in biogenic carbonate

• Rock and fossil record – fossils give much information, what lived when– Rock records formative environment

Fig. 21-7a, p.506

Fig. 21-7b, p.506

Causes of Climate Change

• Astronomical

• Natural Variations in the Carbon Cycle

• Tectonic– Position of the Continents– Volcanic Eruptions

• Human Activity

Astronomical Causes – Sunspot cycles

• The sun’s output varies over time

• Local activity such as sunspots and solar storms has effect on solar output

• Some studies show relationship between changes in global temperature and sunspot cycles

Astronomical Causes – Milankovitch Cycles

Orbital Eccentricity• Earth’s orbit

becomes more/less elongated, changing distance from the Sun.

• This is a cycle on the order of 100,000 years.

Astronomical Causes – Milankovitch Cycles

Axis Shift• Earth’s equator is

presently tilted at a 23.5 ° angle from the orbital plane

• This changes from a minimum (22.5°) to a maximum (24.5°) over a period of approximately 40,000 years

• This change influences length and severity of the seasons

Astronomical Causes – Milankovitch Cycles

Precession (Wobble)• Earth’s axis wobbles in a circle every 26,000

years.

Natural Variations in the Carbon Cycle• Carbon is primary material of biosphere.• 5 times as much carbon in the crust and upper mantle as in the

atmosphere from carbonate rocks.• Fossil fuels primarily carbon.• These materials cycle through atmosphere, changing the carbon

concentration.

Fig. 21-9, p.508

Carbon Reservoirs

Tectonics and climate change

• The position of the continents influences winds and ocean currents.– North and South

America joined, separating Atlantic from Pacific in the tropics.

– Current configuration of continents keeps Arctic Ocean landlocked.

Fig. 16-12, p.384

Volcanoes and climate change

• Volcanic eruptions can cause either warming and cooling of the atmosphere

Volcanoes and climate change• Volcanoes emit ash,

particulates and sulfur compounds, which block sunlight and so cool the atmosphere.

• Volcanoes emit large quantities of CO2, which leads to warming of the atmosphere.

Human contribution to the Greenhouse Effect

• Humans release, fossil fuels,CFCs and other greenhouse gases into the environment.– Concentrations of these gases has increased

in the recent past– The atmosphere has warmed 0.8oC during the

last century

How CO2 in atmosphere relates to temperature

Changes in CO2 Concentration from 1958

Possible Consequences of Global Warming

– Increased temperatures tend to decrease plant productivity.

– Extreme weather events increase (hurricanes, heat waves).

– Changes in biodiversity: increase in extinction rates.

Thermohaline circulation – how global warming could cause global cooling

– Warmer sea surface temperature could slow or stop vertical currents

– This would stop, or re-route the Gulf Stream, which would cool the Earth

– Thermohaline currents have decreased 30% from 1988 – 2000

– Stopping of Thermohaline currents in North Atlantic caused the Younger Dryas Event, 10-11,000 years ago.

Fig. 21-19a, p.519

Fig. 21-19b, p.519

Possible Consequences of Global Warming

• Sea-level changes – sea-level has risen markedly from 1900 to 2000– water expands when warm– Glacial (ice on land) melting is increasing

• Effects on people– Tropical diseases flaring up in new areas– Population stress on food and water supplies as

well as other global systems

Possible Consequences of Global Warming

• Sea-level changes – sea-level has risen markedly from 1900 to 2000– water expands when warm– Glacial (ice on land)

melting is increasing

• Effects on people– Tropical diseases flaring up

in new areas– Population stress on food

and water supplies as well as other global systems

Fig. 21-15, p.514

The Kyoto treaty on greenhouse warming

• Dec. 1997, 160 nations met to discuss global warming– By Feb. 2005 a treaty was ratified by many of

them

– Creates a global trading market for CO2 emissions

– Sets limits and goals– Caps and goals tied to nations’ economies– Developing nations, eg China, India excluded

from CO2 caps

The Kyoto treaty on greenhouse warming

– The U.S. has never ratified the treaty– Treaty supporters argue:

• Wealth not necessarily tied to fuel consumption• Curbing consumption and emissions could help the

economy• Models show the longer we wait, the worse it will get• Consider the alternatives: runaway temperature

changes, famine, global unrest.• The treaty expires in 2012 – the sequel is looking

less than inspired.

Fig. 21-20, p.520

Oxygen Isotope Analysis• Oxygen isotope changes during

production of glaciers via seawater extraction. The ratio of to O18 to O16 in a sample is expressed by scientists as the deviation (designated by the Greek letter δ) from the ratio of isotopes in a standard, where δ O18 = (sample ratio/standard ratio) -1. Note how during low sea level (cold weather conditions, when glaciers are expanding) the ocean becomes enriched in O18, leading to a positive δ O18 value (+1‰), while the glacier becomes depleted in O18, giving it a negative value (-30‰).