Climate change – “science catfight” or not?

The Record Of Climate Change Proxy Data

Causes of climate change Natural Anthropogenic Natural Anthropogenic

Eccentricity 100,000 yrs Obliquity (tilt) 41,000 yrs Precession (wobble) 26,000 yrs Milankovitch cycles

Other factors Solar energy output variability Correlations with sunspot cycles Solar energy output variability Correlations with sunspot cycles

Variations < 0.1% of irradiance

Figure (left) Positive feedback mechanisms

Other factors Continental position Continents in polar regions promote ice sheet growth Continental position Continents in polar regions promote ice sheet growth

Other factors Ocean current circulation patterns

Thermohaline 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 factors Changes in CO 2 CO 2 levels track ice core temps Changes in CO 2 CO 2 levels track ice core temps

Other factors Changes in CO 2 CO 2 levels track ice core temps. May be positive feedback, slight warming releases CO 2 from oceans, causes further warming… Changes in CO 2 CO 2 levels track ice core temps. May be positive feedback, slight warming releases CO 2 from oceans, causes further warming…

Source: GRID/Arendal

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 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 factors Volcanic activity Suspended material reflects solar radiation Volcanic activity Suspended material reflects solar radiation Mt. Pinatubo, 1991 (Photo: USGS)

Volcanoes and Climate Large eruptions can put a lot of ash into atmosphere can reduce amount of sunlight reaching ground surface and cooling Pinatubo eruption million tons of SO 2 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 million tons of SO 2 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 CO 2 Cretaceous warm period may have been caused by large volcanic eruptions Cretaceous chalks record expansion of marine life in warm climate

Human impact

Human Effects on the Carbon Cycle Human activities release ~7.1 Gt* of carbon into the atmosphere each year New plant growth and Air-sea exchange removes ~3.8 Gt/yr …yielding a net atmospheric increase of ~ 3.3 Gt/yr.

Projected Changes in Global Temperature Under Three Different Scenarios Range of uncertainty Continued reliance on fossil fuels increased reliance on nonfossil fuels Rapid conversion to cleaner and more to cleaner and more resource-efficient technologies

Likely temperature change by the end of the 21st century, relative to A.Fossil-fuel intensive world B.More conservation- oriented world

Consequences 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 projected to reduce the north polar ice cap, disrupting Arctic ecosystems, but possibly improving navigation.

Land surface slope near shoreline influences effect of sea level change

Raisz

Over next century, Arctic could warm by ˚C (similar to last interglaciation) Last interglacial caused by changes in Earth’s tilt and orbit Next century changes due to increased CO 2 in atmosphere

Figure 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 gases Conservation Alternative energy Sequestration Biomass Deep ocean Geological Conservation Alternative energy Sequestration Biomass Deep ocean Geological

Deep ocean injection Liquid CO 2 denser than water in cold high pressure environment

UNEP/GRID Per capita emissions

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 With and Without the Montreal Protocol