Climate Change Climate Variability vs Climate Change 1

Climate Change

Climate Variability vs. Climate Change 1. Climate Variability: • Changes over seasons and years; • yearly fluctuations (above or below) long-term average • 30 yr average : “climatological normals” • Example Duluth climate normals 1981 -2010 • There is significant variability around these normals • Example: normal daily max temp for Duluth on Apr 30 is 56. 6 but not every Apr 30 in 1981 -2010 had a max temp of 56. 6 This year to year fluctuation around the normal is

In addition to averages, ranges are part of climatological normals.

• Climate variability is caused by (for example) : • Volcanic eruptions which can have a cooling effect. • El Nino-La Nina , cause snowy/ non. M! snowy , warm / cold winters in Duluth. R E T O SH RT

2. Climate Change long-term continuous change to normals (averages, ranges). § long term : many decades § slow, gradual § requires scientific (or other) records

Causes of Climate Change “Climate Forcings” • Natural or anthropogenic disturbances to global energy balance. • Positive forcing: induces an increase in global mean surface temperature • Negative forcing: induces a decrease

Climate forcing 1. Plate tectonics • geologic time scales • Changing continent, ocean sizes & locations, changing atmospheric composition, • changing sizes and locations of mountain ranges • Change atmospheric and oceanic circulation • Examples….

300 -360 million years ago current

Triassic 200 -250 million years ago Aridity, monsoons, humid regions

Over past few million years, Tibetan Plateau and Himalayas have been rising, causing increased aridity in western China and central Asia

Climate forcing 2. Astronomical periodicities • Milankovitch forcings • “Wiggle” • “Wobble” • “Stretch”

“Wiggle”: obliquity • Tilt of Earth’s axis changes • 22. 1° – 24. 5° • Strength of seasons • Especially High latitude variation in insolation • 41, 000 year periods

“Wobble”: precession • Earth’s axis wobbles • Changes timing of perihelion and aphelion • Timing and intensity of seasons • 27, 000 yr periods

On Jan 4, earth is 3% closer to sun than on July 4

“Stretch”: eccentricity • Shape of earth’s eccentric orbit changes • Changes the intensity of solar radiation received at aphelion and perihelion • 100, 000 yrs

Effect of these three: Global temperature fluctuations of ± 2 – 5 degrees C per 10, 000 yrs match closely with glacial-interglacials over past 100, 000 yrs

• Animation of Milankovitch cycles

Book Stuff for Test • Ch 1: pp. 12 -24 • Ch. 2: pp. 35 -50 seasons • Ch. 3: pp. 56 -69 • Ch 4: pp. 481 -499

Climate Forcing 3. Solar Variability Sunspot cycle 11 year ± 1 W/m 2 change in solar constant (1372 W/m 2) Effects UV radiation Example: Maunder Minimum 1645 -1715: period of reduced sunspot activity; global temp decrease of 0. 5 C Sunspot activity

Climate Forcing 4. Volcanic Eruptions Big, explosive eruptions can inject dust and sulfur dioxide into stratosphere. change into sulfuric acid droplets that reflect (backscatter)solar radiation Causes global average cooling of tenths of a degree C 1 -2 years following eruption. Mt Pinatubo 1991 example Not all volcanoes are explosive enough to reach stratosphere; not all have high SO 2

Aerosol content around globe before and after June 19 Pinatubo eruption. (Red is higher aerosol content).

Climate forcing 5. Human-Induced changes Atmospheric composition (increased concentration of GG and aerosols) Land use/ Land cover changes (urban surfaces, agricultural practices, deforestation, overgrazing)

Timescale Differences of Forcings • Plate tectonics : millions • Astronomical (Milankovitch) : 10 s of 1000 s • These are irrelevant when looking at past 100 years • Solar, Volcanic, Anthropogenic : relevant to short timescales

Radiative Forcing and Radiative Feedback

Radiative Forcing • Globally and annually averaged changes in radiation balance at top of atmosphere. • Plate tectonics and Milankovitch are not radiative forcings • Solar, volcanic, anthropogenic are radiative forcings

A; BEDO! Top of the atmosphere 70 OUT 70 IN 12 104 58 23 58 116 47 98

GG : positive radiative forcing agent Sun’s energy : positive radiative forcing agent Volcanic eruptions : negative radiative forcing agent

Quantifying radiative forcing • How much a forcing factor alters global and annual average radiation balance at top of atmosphere, relative to 1750 (beginning of Industrial Revolution) In 2011, estimated radiative forcing from anthropogenic = 2. 29 Wm-2 from Fifth IPCC report

Mechanism of Greenhouse Warming • 1. the simple explanation:

Increased green -house gas concentration: More of the longwave emitted from surface is absorbed by atmosphere and less goes out to space. Net solar incoming exceeds longwave loss: Increased temperature