Climate Change: Theory and Forecasts David Gay National Atmospheric Deposition Program (NADP) (217)

2 Two Parts 1.What exactly is climate change? a.Theory b.What we know 2.Forecasts

3 So, what is “Climate Change”?

4 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.)

5 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?

6 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

7 So? More than just temperature Precipitation (amount and patterns) Atmospheric pressure Humidity Circulation changes Number of storms, droughts, freezes, etc. And more….

8 Average Temperatures, in ◦ C

9 Type of Ecosystem, w T and P

10 Water Cycle

11 Radiation Balance “The Greenhouse” Example Your stove top

12 Radiation Balance

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14 “Effective” Greenhouse Gases Atmospheric Window

15 So, what do we know? INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (World Meteorological Organization; UN Env. Program)

16 Carbon Dioxide Concentration Over Time

17 Methane also a Greenhouse Gas

18 Quiz How much has the earth warmed in the last 150 years?

19 Answer ≈ 0.95°C (1.62 °F) since 1850

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21 Historic Thermometer Records

22 “Diurnal Temperature Range”

23 Temperature Trends, ◦ C

24 Changes In…..

25 Sea-Level Rise Total Change = +170 mm or +6.7 inches

26 Causes of Sea Level Rise Sea-level rise during the 20 th century (cm) Ocean thermal expansion4+ Mountain glaciers5 Greenland & Antarctic ice2 Total11 Observed rise17

27 Arctic Sea Ice Sep 1979Sep = 4.3 x10 6 km 2, record low

28 Glacial Retreat Argentiere Glacier, French Alps

29 Trends in Precipitation

30 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.

31 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

32 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

33 Historical Perspective of Temperatures

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35 Human Contribution to Climate Change (in one slide) IPCC, 2007

36 Causes of climate change Climate change is driven by five causes (forcings) Internal components of the climate system respond by changing and interacting in many ways Changes in atmospheric composition (greenhouse) Volcanic eruptions

37 Natural Causes of Climate Change ( non anthropogenic)

38 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 today Milanchovitch Cycles, Orbital Changes

39 Precession of the equinoxes (23k years) Oval/circular changes Inclination Change

40 Changes in Solar Energy Output

41 The smoothed sunspot curve correlate with temperature Some intervals almost entirely lack sunspots, such as the Maunder sunspot minimum from 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

42 Other Natural Causes Mt Pinotubo

43 The Modeled Future

44 CO 2 Should Increase

45 Predicting Temperature Global Climate Models (GCMs) Physical equations Lots of computing Divide the globe into little boxes

46 Forecast Temperatures

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48 Projections of Surface Temperatures

49 Volcanoes GH gases Solar With GH gases W/out GH gases IPCC, 2007 How Good Are the Models?

50 Further Reading Intergovernmental Panel on Climate Change (IPCC) UN organization (Weather Meteorological Office) Summary for the physical science basis

51 Figures from W. Ruddiman, 2008; Earth’s Climate: Past and Future

52 Climate Change: Theory and Forecasts David Gay National Atmospheric Deposition Program (NADP) (217)