Global Warming Human-driven Climate Change

Climate Change is Not New The Earth has historically gone through alternating periods of global warming and global cooling, sometimes quickly other times over prolonged periods of time. – Cold Periods = glacial period – Warm Periods = interglacial period

How do we know this? Drilling holes – Ice cores taken from old glaciers in Greenland and Antarctica – Analyze air bubbles trapped in the ice to discover the tropospheric composition of the past – Also can drill cores from the bottom of lakes, swamps, and ponds – After considering all data, a consensus is reached. IPCC (Intergovernmental Panel on Climate Change) Consists of over 2,000 climate experts from 70 nations

Factors that lead to Climate Change Changes in the greenhouse effect – Natural changes in atmospheric composition of green house gases Variations in the sun’s energy reaching Earth – Solar cycles – Changes in Earth’s orbit (tilt and position) Changes in the reflectivity of Earth’s atmosphere and surface – Volcanic eruptions – Change in sea ice levels

The Greenhouse Effect Certain atmospheric gases absorb outbound infrared (IR) radiation and then reradiate it in all directions including downward. Some of the reradiated IR reaches the ground and lower atmosphere to make the Earth warmer than it would be without the greenhouse gases. Much like the glass of a greenhouse allows in light but traps heat. Without any greenhouse gases, Earth would chill to –18 o C. Water is the main greenouse gas, but it’s self limiting due to precipitation. CH 4

Greenhouse Effect CO 2 CH 4 CFC

Greenhouse Gases Other gases help CO 2. All have significant natural sources except CFC’s. Methane = natural gas from swamps & rice paddies, oil & gas wells, coal mines, land fills, cow & termite flatulence, & decomposition. CFC’s being phased out, used in AC and as propellants (hair spray). Low altitude ozone partly from man’s pollution. N 2 O from burning, lightning, moist soils. CH 4 CO 2 N2ON2O O3O3 e.g. CCl 2 F 2 Percentage indicates relative importance, not relative abundance.

Relative Global Temperature Variation Mean annual temperatures are indicated as a deviation from the global mean. 5 o C total temperature rise since last ice age (18,000 years BP) or 0.03 o C per century, about half of rise is due to increasing solar output. The 0.5 o C rise in the last 25 years looks very significant, = 2 o C per century. 0.6

Global Warming Since begins the period where thermometer readings are available worldwide. Annual averages for entire world compared to averages for Larger rise projected during 21st century.

CO 2 Concentration Vs. Time Has risen rapidly since industrial revolution due to fossil fuel burning. Many natural sources: volcanoes, burning, respiration, decomposition. Rise is less than expected. Key cause of greenhouse effect. Fossil Fuels = coal, oil, natural gas, peat Garrison, 2005

CO 2 may be approaching 3X the preindustrial level in 2100.

What causes the zig zag detail in the curve?

Rising Carbon Dioxide (CO 2 ) Levels Rapid rise from coal, gas, and oil burning since Causes greenhouse effect, i.e. global warming. Missing CO 2 puzzle: concentration is lower than predicted by emissions. Storage in ocean or plants?

Sea Level Change in Last 20,000 Years Water supplied by rapid glacial retreat. Little change in last 6,000 years. 100 m rise in 11,000 years = 9.1 mm/yr average 18.2 m/yr horizontal shoreline shift on VA Coastal Plain

Projected Sea Level Rise in This Century Three different estimates. Note the accelerating rate of rise! Worldwide changes are termed eustatic sea level changes.

Causes of Sea Level Sea Level Rise This Century Note the Antarctic Ice Sheet may actually grow in spite of global warming & limit sea level rise. 57% of the sea level rise will result from simple expansion of seawater as it warms.

Effects of Rising Sea Level I-95 Coastal Plain Virginia Beach X Uplift along an active continental margin may offset sea level rise in CA Like the East coast in early Tertiary time. Like the West coast.

Coastline Variation Due To Glacially-Induced Sea Level Changes

What does rising sea level mean to islanders? Land is inundated & barrier reef provides less wave protection. Great tsunami of December 2004 washed over this island. Many died. Island in Maldives

More about oceans… Oceans help moderate surface temperatures by removing about 29% of the excess CO 2 in the atmosphere. They also absorb heat and transfer some of it to the deep ocean. Ocean currents are connected and move heat from the tropics to the poles. Oceans at the tropics are more salty than they were, whereas water at the poles is less salty. Why does this even matter?

Effects on the Oceans Global warming may affect global precipitation patterns and alter the distribution, severity, and frequency of droughts, floods, and storms. Evaporation from the oceans could mean more water vapor in the air, thus increasing global warming. It could slow down the currents that draw warm Gulf Stream waters northward in the Atlantic.