Climate Change Flashcards
What is the climate system?
- Complex system consisting of 5 major components:
- The atmosphere, hydrosphere, cryosphere, lithosphere and biosphere
- Control the climate through the integration between the different spheres
Outline environmental change
- Climate change drives shift in geomorphological processes
- Examination of relict landscapes as a reflection of past environmental change
Describe the temp since 2000
- General trend is increasing
Outline post industrial climate change
- For the most of the last 1000 years, the climate has been cooler than normal
- Since late 1800s – general increase
- All 30-year periods have been colder since the last few 30-year periods
Outline changes in climate over the last 10,000 years
- The Holocene
- Regional variations of temp
- Variations which cause flatlines
- Climate has become a lot more stable
- Rapid warming and gradual cooling – occur periodically
- When Antarctica is warm, Greenland is cold
- Changes from 16 to 18 degree in human lifetime
Outline changes in climate over the last 1 million years
- Major climate cycles
- Climate instability with rapid shifts – 10 or more degrees change
- Occur on longer timescales
- CO2 is at highest level seen since cretaceous, but temp is lower than at last interglacial
- Change in pace – magnitude of change is smaller but shift from hot to cold is quicker
Outline changes in climate over last 4.5 billion years
- Holocene stable compared to last million years before
- Rapid shifts in cold to warm – occurs all the way through the last 2 million years
- Climate unstable since earth was formed
- Evidence from records of ocean and ice
What are the causes of long term climatic changes
- Causes – changes in plate tectonics, earth’s orbit and suns strength – external forcing
- Climate variations (internal responses) – changes in atmosphere, ice, vegetation, ocean and land surface
What is the pliocene pleistocene transition?
The Earth underwent a major transition from the warm climates of the Pliocene to the Pleistocene ice ages between 3.2 and 2.6 million years ago. The intensification of Northern Hemisphere Glaciation is the most obvious result of the Plio-Pleistocene transition
Describe the earths orbit
- Spins on axis once a day
- Passes through both poles
- 1 year to rotate around sun
- Main cause of seasons, solstices, changes in day length is changing position of the tilted earth with respect to the sun
What are elliptical shapes?
Elliptical shapes cause the distance to the sun to change depending on earths position in its orbit
What is perihelion?
Position where the earth is closest to the sun
What is aphelion?
Position where the earth is furthest away from the sun
How can earths orbit affect climate?
Climate ca be affected by changes in:
- Distance from sun
- Angle of inclination towards/away from sun
What is the orbital theory of ice ages?
- Ideas relating to orbital variations to climate were developed in 19th century (James Croll)
- “Temporal changes in insolation that are astronomically driven cause significant changes in the global climate, and in particular, that they account for much of the climatic variability of the Quaternary glacial-interglacial cycles”
What are the 3 aspects of the earth’s orbit which vary due to gravitational forces in the solar system
1 – eccentricity – shape of orbit
2 – obliquity – tilt
3 – precession – amount of wobble
- Past orbital variations can be retroacted or back calculated
- Allows isolation changes to be calculated
What is isolation?
- Refers to the quantity of solar radiation reaching the top of atmosphere
- Usually expressed in Watts per square metre Wm-2
- Isolation received varies with latitude and with the seasons
What are isolation curves?
- Insolation curves can be calculated for a particular latitude and time of year
- Often you will see June insolation of 65 0N used as this is thought to be particularly important in climate forcing and is the region where the major mid-latitude ice sheets form
What is eccentricity?
- Eccentricity (e) describes the shape of the earth’s elliptical orbit e = c/a
- Where c = focus or orbit and a = semimajor axis
- Eccentricity varies between approx. 0 and 0.06
What is obliquity?
- Describes the angle of tilt of the Earth’s axis of rotation
- Earth’s axis of rotation is tilted – currently 23.5 degrees
- Controls the geographic distribution of insolation
What does increased tilt affect?
- Increased tilt affects the poles proportionally more than the mid latitudes
- Polar latitudes receive less insolation than low latitudes
- This imbalance is the driving force behind the global climate system
- Changing the angle of the tilt causes changes in energy balance between equator and poles
What are the biggest impacts of changes in obliquity?
- Biggest impact of changes in obliquity are felt in high latitudes
- Amplified seasonal cycles occur with greater obliquity
- Greatest affect felt at 660 N
- Varies between 22.2 – 24.5 degrees over a 41 ka periodicity
What is precession?
- Has two components – axial and elliptical
- This changes the position of the earth on its annual orbit around the sun at the solstices and equinoxes
What is axil precession?
Wobble, caused by gravitational pull of the sun and moon – 25,700-year cycle
What is elliptical precession?
Gradual rotation of the elliptical orbit
What is precession of the equinoxes?
Precession of the equinoxes is a mechanism that affects the season reached at perihelion (the point on the orbit when the Earth is closest to the sun)
What is elliptical and axial precession?
- Precession of the equinoxes-
- Affects the season when the orbit is at perihelion
- 23 ka cycle
- Closely related to eccentricity
- Have to multiply precession of the equinoxes by eccentricity to get useful measure of precession
- Climate impact of precession is greatest at low latitudes
What are the causes of short term climate change?
Ocean, Atmosphere and Land factors
- Solar input
- Earth-sun geometry
- Stellar dust
What is thermohaline circulation (THC)?
The movement of seawater in a pattern of flow dependent on variations in temperature, which give rise to changes in salt content and hence in density
How is thermohaline circulation linked to climate change?
- Regulates climate
- Reduction in this would lead to colder conditions and enhance ice
What are Heinrich events?
- Episodes of ice rafting
- Distinctive layers of ice-rafted debris – carbonate rich deposits
- Deposited from icebergs drifting eastwards across north atlantics
- Found in marine cores from 40-500N
What is the salt oscillator hypothesis?
Put forward as a mechanism to explain how salinity oscillations in the Atlantic Ocean could modulate the strength of AMOC and cause the D-O cycles of the last ice age.
What is a bi-polar teleconnection?
- Link records of climate from north and south hemisphere from levels of methane
- Methane is transported in atmosphere
- Can align methane records
- When Greenland is warming, Antarctica is cooling
What is a bi-polar seesaw?
- Colling in N Atlantic coincides with warming in the south
- Sustained heating of south would increase evaporation rates and therefore sea-surface salinity
- Leads to re-establishment of AMOC transferring heat north and allowing south to cool
What is heat piracy?
- Elaboration on bipolar seesaw – deep ocean currents
- Ocean circulation can act as pendulum and can be influenced at deep water sources at either end
- Suggests that NADW could control the oscillation in both hemispheres
What were the main forcing during the Holocene?
- Insolation – peak in northern hemisphere in early Holocene
- Volcanic forcing – based on sulphate records – typically negative forcing
- Changes in solar activity – strength of radiation –
- Changes in greenhouse gases – dramatic rise
What is solar irradiation?
The solar irradiance is the output of light energy from the entire disk of the Sun, measured at the Earth
How does solar activity affect climate?
- Changes in the UV radiation affects stratospheric ozone, leading to associated temperature variations and changes in the tropospheric westerly jet streams
- Sun emitting less energy causes changes in climate
How has volcanoes affected climate?
- Large eruptions cause cooling through sulphate gases that absorb solar radiation
- A negative forcing
- Possible global cooling – short lived – only has an effect for 2-3 years
What are some volcanic influences on climate?
- Toba ‘super eruption’
- 28000km3 of magma erupted
- Largest known eruption in the Quaternary
- 3.5-330 x 10(10) kg sulphate erupted into atmosphere
- Possible trigger for enhanced global cooling
What is the little ice age?
- 1300-1850 AD
- Coldest period in Holocene triggered by covarying low orbital forcing, major volcanic eruptions and low solar irradiation
Outline all forcing on climate
1) Orbital forcing
2) Solar irradiance and large volcanic eruptions
