Earths Climate System Climate long term atmospheric conditions

Earth’s Climate System • Climate – long term atmospheric conditions in a region • Earth’s climate includes interactions of: – Atmosphere – Hydrosphere – Geosphere – Biosphere – Cryosphere • Climate system – exchanges of energy and moisture between these spheres

Earth’s Climate System

Earth’s Climate System • Feedback loops – modify atmospheric processes – Positive feedback loops – enhance initial change – Negative feedback loops – counteract initial change

Determining Causes of Earth’s Climate Change • Paleoclimatology • Proxy data – indirect evidence using natural recorders of climate variability – – – Sea floor sediments Coral deposits Glacial ice rings Tree rings Pollen Historical documents

Temperature: the last 400, 000 years From the Vostok ice core (Antarctica)

Natural Climate Change • External Forcing: – The agent of change is outside of the Earth -atmosphere system • Internal Forcing: – The agent of change is within the Earthatmosphere system itself

External Forcing • Variations in solar output • Orbital variations • Meteors

Natural Causes of Climate Change • Solar energy changes – Variable energy from the Sun over time – Luminosity – Sunspots

Solar Variations § Sunspots correlate with solar activity p More sunspots, more solar energy • Sunspots are the most familiar type of solar activity.

SOLAR ACTIVITY • Sunspots are the most familiar type of solar activity.

THE SOLAR CYCLE • Sunspot numbers increase and decrease – over an 11 -year cycle • Observed for centuries. • Individual spots last from a few hours to months. • Studies show the Sun is in fact about – 0. 1% brighter when solar activity is high.

The Seasons • The Earth has seasons because the axis is tilted. • Earth rotates on its axis as it orbits the Sun. • Earth’s axis ALWAYS points in the same direction… • but Earth’s location in its orbit around the Sun determines whether the NH or SH is pointed toward the Sun.

The Seasons • NH Summer Solstice – June 20 -21 • NH Autumnal Equinox – September 22 -23 • NH Winter Solstice – December 21 -22 • NH Vernal Equinox – March 20 -21

Earth’s orbit: an ellipse • Perihelion: place in the orbit closest to the Sun • Aphelion: place in the orbit farthest from the Sun

Earth’s orbit: an ellipse • Perihelion: place in the orbit closest to the Sun • Aphelion: place in the orbit farthest from the Sun

THE MAUNDER MINIMUM • An absence of sunspots was well observed – from 1645 to 1715. • The so-called “Maunder minimum” coincided with a cool climatic period in Europe and North America: – “Little Ice Age” • The Maunder Minimum was not unique. • Increased medieval activity – correlated with climate change. 17

Natural Causes of Climate Change • Variations in Earth’s Orbit • Milankovitch Theories – Eccentricity of Earth’s orbit – Obliquity of Earth’s axis – Precession of Earth’s axis

Orbital changes • Milankovitch theory: • Serbian astrophysicist in 1920’s who studied effects of solar radiation on the irregularity of ice ages • Variations in the Earth’s orbit – Changes in shape of the earth’s orbit around sun: • Eccentricity (100, 000 years) – Wobbling of the earth’s axis of rotation: • Precession (22, 000 years) – Changes in the tilt of earth’s axis: • Obliquity (41, 000 years)

Eccentricity: period ~ 100, 000 years

Natural Causes of Climate Change • Volcanic eruptions • Volcanic ejecta may block sunlight • Need many eruptions in short time period • Not observed in recent history

Natural Causes of Climate Change • Movement of Earth’s Plates – Change ocean circulation – Extremely slow process – Climate change would be very gradual over millions of years • Linked to Pleistocene Ice Age, Little Ice Age, Medieval Warm Period

Documenting Human-Caused Climate Change • Intergovernmental Panel on Climate Change (IPCC) – Global group of scientists – Published assessments since 1990 – Predict global temperature changes of 1. 4– 5. 8°C (2. 5– 10. 4°F) • Climate change models can mimic modern conditions only if human emissions are taken into account.

Atmosphere’s Greenhouse Effect • Global warming – increase in Earth’s global temperatures • Greenhouse effect – keeps Earth’s surface habitable – Incoming heat energy is shorter wavelengths – Longer wavelengths – some trapped, some escape, net warming effect

Earth’s Heat Budget • Addition to or subtraction from heat on Earth • Incoming radiation from Sun shorter wavelengths • Outgoing radiation from Earth longer wavelengths • Rates of energy absorption and reradiation must be equal

Earth’s Heat Budget

Greenhouse Gases • Water vapor – Most important – 66– 85% of greenhouse effect • Carbon dioxide – Natural part of atmosphere – Greatest relative contribution from human activities – Burning of fossil fuels

Atmospheric Carbon Dioxide

Greenhouse Gases • Methane – Second most abundant human-caused greenhouse gas – Great warming power per molecule – Landfill decomposition – Cattle • Other trace gases – Nitrous oxide, CFCs, ozone

Human-Caused Greenhouse Gases