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Climate Change: Theory and Forecasts. David Gay National Atmospheric Deposition Program (NADP) dgay@uiuc.edu, (217) 244-0462. Two Parts What exactly is climate change? Theory What we know Forecasts. So, what is “Climate Change”?. First, what is climate?. Definition
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Climate Change: Theory and Forecasts David Gay National Atmospheric Deposition Program (NADP) dgay@uiuc.edu, (217) 244-0462
Two Parts • What exactly is climate change? • Theory • What we know • Forecasts
First, what is climate? • Definition Average course or conditions of weather at a place, usually over a period of years, as exhibited by • Temperature • Wind velocity • Precipitation (Webster’s) • Prevailing set of weather conditions (temperature, humidity, etc.)
So, can WE change climate? • Thomas Jefferson guessed we could in early 1800’s • Trees in VA • Started making measurements • Urban concrete, no trees • Chemical composition of the atmosphere • Sensible energy vs. latent heating • Albedo changes • Natural changes (ice ages, warm periods) • Changing evaporation/precipitation (trends) • Other patterns (Malenkovitch cycles, el Nino/la Nina) • Cloud cover changes?
Definition of Climate Change IPCC usage: • Any change in climate over time, whether due to natural variability or from human activity. Alternate: • Change of climate, attributed directly or indirectly to human activity, that • Alters composition of global atmosphere and • Is in addition to natural climate variability observed over comparable time periods
So? More than just temperature • Precipitation (amount and patterns) • Atmospheric pressure • Humidity • Circulation changes • Number of storms, droughts, freezes, etc. • And more….
Radiation Balance“The Greenhouse” • Example Your stove top
“Effective” Greenhouse Gases Atmospheric Window
So, what do we know? • INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (World Meteorological Organization; UN Env. Program) • http://www.ipcc.ch/
Quiz • How much has the earth warmed in the last 150 years?
Answer ≈ 0.95°C (1.62 °F) since 1850
Sea-Level Rise Total Change = +170 mm or +6.7 inches
Sep 1979 Sep 2003 Arctic Sea Ice 2007 = 4.3 x106 km2 , record low
Glacial Retreat Argentiere Glacier, French Alps
IPCC Summary of Observations • Global mean surface temperatures have risen • By 0.74°C ± 0.18°C over the last 100 years (1906–2005) • 2005 was one of two warmest years on record • Land regions have warmed at a faster rate than the oceans. • Changes in extremes of temperature are consistent with warming of climate • Widespread reduction in number of frost days in mid-latitude regions, • Increasing number of warm extremes & reducing number of daily cold extremes observed in 70 to 75% of land regions, and • Most marked changes are for cold (lowest 10%, based on 1961–1990) nights, rarer over 1951 to 2003 period.
IPCC Summary (cont.) • Sea-surface temperatures warming at all latitudes over all oceans, • Urban-heat island effects real but local, have not biased large-scale trends, • Average arctic temperatures increased at almost twice global average in past 100 years, • Lower-tropospheric temperatures increases slightly greater than those at surface between 1958 to 2005
IPCC Summary (cont.) • Lower stratospheric temperatures cooling since 1979, • Precipitation has generally increased over land north of 30°N between 1900 to 2005, but downward trends dominate tropics since 1970s, • Droughts more common, especially in tropics and subtropics, since 1970s, • Changes in large-scale atmospheric circulation apparent
Human Contribution to Climate Change (in one slide) IPCC, 2007
Causes of climate change Volcanic eruptions Changes in atmospheric composition (greenhouse) • Climate change is driven by five causes (forcings) • Internal components of the climate system respond by changing and interacting in many ways
Milanchovitch Cycles, Orbital Changes today • Earth orbital changes • Result from cyclic variations in Earth's orbit around the Sun • Alter the amount of solar radiation (insolation) received on Earth by season and by latitude
Precession of the equinoxes (23k years) Oval/circular changes Inclination Change
The smoothed sunspot curve correlate with temperature Some intervals almost entirely lack sunspots, such as the Maunder sunspot minimum from 1645-1715 AD These sunspot minima occurred during the Little Ice Age when the sun was 0.25% weaker Solar activity was generally high during the Medieval Warm Period
Other Natural Causes Mt Pinotubo
Predicting TemperatureGlobal Climate Models (GCMs) • Physical equations • Lots of computing • Divide the globe into little boxes
Volcanoes Solar GH gases With GH gases W/out GH gases IPCC, 2007 How Good Are the Models?
Further Reading • Intergovernmental Panel on Climate Change (IPCC) • UN organization (Weather Meteorological Office) • http://www.ipcc.ch/ • Summary for the physical science basis • http://ipcc-wg1.ucar.edu/wg1/wg1-report.html