Climate change – “science catfight” or not?. The Record Of Climate Change Proxy Data.

Climate change – “science catfight” or not?

The Record Of Climate ChangeThe Record Of Climate Change

Proxy Data Proxy Data

Causes of climate changeCauses of climate change

Natural Anthropogenic

Natural Anthropogenic

Eccentricity 100,000 yrs

Obliquity (tilt) 41,000 yrs

Precession (wobble) 26,000 yrs

Milankovitch cycles

Other factorsOther factors Solar energy output variability

Correlations with sunspot cycles

Solar energy output variability Correlations with sunspot cycles

Variations < 0.1% of irradiance

Figure 21.21 (left)Figure 21.21 (left)

Positive feedback mechanisms

Other factorsOther factors Continental position

Continents in polar regions promote ice sheet growth

Continental position Continents in polar regions promote ice sheet

growth

Other factorsOther factors Ocean current circulation patterns Ocean current circulation patterns

Thermohaline circulationThermohaline circulation

Temperature or salinity induced density differences

Cold water sinks to bottom at high latitudes

Restricted flow to poles may promote ice sheet growth

Temperature or salinity induced density differences

Cold water sinks to bottom at high latitudes

Restricted flow to poles may promote ice sheet growth

Other factorsOther factors

Changes in CO2

CO2 levels track ice core temps

Changes in CO2

CO2 levels track ice core temps

Other factorsOther factors

Changes in CO2

CO2 levels track ice core temps.

May be positive feedback, slight warming releases CO2 from oceans, causes further warming…

Changes in CO2

CO2 levels track ice core temps.

May be positive feedback, slight warming releases CO2 from oceans, causes further warming…

Source: GRID/Arendal

Climate Variations and Tectonics

Climate Variations and Tectonics

These are linked in various ways Plate motions mean moving large continental masses

around Move away from equator: more water to absorb solar

radiation near equator, overall warming Move towards equator: less water, can cool General change in ocean circulation patterns

Uplift of large mountains can change atmospheric circulation

Opening of oceans mean large lava outputs Likely add gases to aid warming through greenhouse effect

These are linked in various ways Plate motions mean moving large continental masses

around Move away from equator: more water to absorb solar

radiation near equator, overall warming Move towards equator: less water, can cool General change in ocean circulation patterns

Uplift of large mountains can change atmospheric circulation

Opening of oceans mean large lava outputs Likely add gases to aid warming through greenhouse effect

Recent TimesRecent Times

Last 2 million years, have had several ice ages

Most recent peaked ~20,000 years ago

Last 2 million years, have had several ice ages

Most recent peaked ~20,000 years ago

Other factorsOther factors Volcanic activity

Suspended material reflects solar radiation

Volcanic activity Suspended material reflects solar radiation

Mt. Pinatubo, 1991 (Photo: USGS)

Volcanoes and ClimateVolcanoes and Climate Large eruptions can put a lot of ash

into atmosphere can reduce amount of sunlight reaching

ground surface and cooling Pinatubo eruption 1991

20 million tons of SO2 put in the atmosphere

Reflected 2-4% of incoming solar radiation

Led to average cooling of earth by 0.5-1°C that persisted for ~1-2 years

Large eruptions can put a lot of ash into atmosphere can reduce amount of sunlight reaching

ground surface and cooling Pinatubo eruption 1991

20 million tons of SO2 put in the atmosphere

Reflected 2-4% of incoming solar radiation

Led to average cooling of earth by 0.5-1°C that persisted for ~1-2 years

“Cloud” from Mt. Pinatubo eruption

Temperature change

1815 eruption of Tambora volcano in Indonesia lowered global temperature 3°C

1816 know as “the year without summer”

1815 eruption of Tambora volcano in Indonesia lowered global temperature 3°C

1816 know as “the year without summer”

Source: NASA

But, volcanoes also emit CO2But, volcanoes also emit CO2

Cretaceous warm period may have been caused by large volcanic eruptions

Cretaceous warm period may have been caused by large volcanic eruptions

Cretaceous chalks record expansion of marine life in warm climate

Human impactHuman impact

Human Effects on the Carbon CycleHuman Effects on the Carbon CycleHuman activities release~7.1 Gt* of carbon into

the atmosphere each year

New plant growth andAir-sea exchange

removes ~3.8 Gt/yr

…yielding a netatmospheric increase

of ~ 3.3 Gt/yr.

Projected Changes in Global Temperature Projected Changes in Global Temperature Under Three Different ScenariosUnder Three Different Scenarios

Range ofuncertainty

Continued reliance on fossil fuels

increased reliance on nonfossil fuelsincreased reliance on nonfossil fuels

Rapid conversionRapid conversion to cleaner and more to cleaner and more

resource-efficient technologiesresource-efficient technologies

Likely temperature change by the end of the 21st century, relative to 1960-1990

A. Fossil-fuel intensive world

B. More conservation-oriented world

Consequences for sea levelConsequences for sea level

Melting land ice

Thermal expansion of water

>100 m rise since last glacial maximum

Melting land ice

Thermal expansion of water

>100 m rise since last glacial maximum

Global warming is Global warming is projected to reduce the projected to reduce the

north polar ice cap, north polar ice cap, disrupting Arctic disrupting Arctic ecosystems, but ecosystems, but

possibly improving possibly improving navigation.navigation.

Land surface slope near shoreline influences effect of sea level change

Raisz

• Over next century, Arctic could warm by 3 - 5 ˚C (similar to last interglaciation)• Last interglacial caused by changes in Earth’s tilt and orbit• Next century changes due to increased CO2 in atmosphere

Figure 18.6Figure 18.6

2005 study suggesting that hurricane intensity (more cat 4 and 5) has increased over last 15 years, corresponding to ~0.3° increase in temperature

Why are these linked?

Reducing greenhouse gasesReducing greenhouse gases

Conservation Alternative

energy Sequestration

Biomass Deep ocean Geological

Conservation Alternative

energy Sequestration

Biomass Deep ocean Geological

Deep ocean injectionDeep ocean injection

Liquid CO2 denser than water in cold high pressure environment

Liquid CO2 denser than water in cold high pressure environment

UNEP/GRID

Per capita emissions

Another example of human effect on atmospheric composition:Ozone depletion

Another example of human effect on atmospheric composition:Ozone depletion

Ozone gas in smog : bad Ozone in stratosphere: good

Protects from UV radiation which damages cells

Depleted by reacting with human made compounds (particularly CFCs)

Ozone gas in smog : bad Ozone in stratosphere: good

Protects from UV radiation which damages cells

Depleted by reacting with human made compounds (particularly CFCs)

Ozone hole found near Antarctica in 1985

Led to passage of legislation (Montreal Protocol) to get rid of CFCs

Projected Changes in Ozone Concentration Projected Changes in Ozone Concentration With and Without the Montreal ProtocolWith and Without the Montreal Protocol