An introduction to global climate change On August 29, 2005, Hurricane Katrina landed east of New Orleans The costliest ($134 billion in damage) storm ever The deadliest storm (killing 1,800) since 1928 Leaving mountains of debris, ruined homes and lives A month later, Hurricane Rita hit Louisiana and Texas 2005 had a record 27 named storms 2007 had 15 and 2008 had 18 named storms There is a link between hurricanes and global warming Warmer oceans create humid air, leading to hurricanes

Number of category 4 and 5 hurricanes

Structure and temperature of the atmosphere

Weather Weather: day-to-day variations in temperature, air pressure, wind, humidity, precipitation Climate: the result of long-term regional weather patterns Meteorology: the study of the atmosphere (weather and climate) The atmosphere-ocean-land system is a huge weather engine Driven by the Sun and affected by Earth’s rotation and tilt Solar energy is reflected (29%) or absorbed by Earth Absorbed energy heats the ocean, land, and atmosphere

Solar-energy balance

Climate is … Climate: the general patterns of weather that characterize different regions of the world Climate results from all the combined elements of General atmospheric circulation patterns and precipitation Wind and weather systems Rotation and tilt of Earth, which creates seasons

Synopsis of global climate change In 2007, scientists from the Intergovernmental Panel on Climate Change (IPCC) sifted through thousands of studies and published the Fourth Assessment Report (AR4) The report concluded that warming of the climate is unequivocal The atmosphere and oceans are warmer Sea levels are rising and glaciers are melting There are more extreme weather events

Annual mean global surface temperature anomalies

The IPCC’s report The report concluded that it is very likely (90% probability) that warming is caused by human factors Increased greenhouse gases (GHGs) trap infrared radiation GHGs come from burning fossil fuels Along with deforestation The major GHG: CO2 Responses to climate change Mitigation: reducing GHG emissions Adaptation: adjusting to climate change

Atmospheric carbon dioxide concentrations

IPCC Founded in 1988 by the UN Environmental Program and the World Meteorological Society to provide accurate and relevant information leading to understanding human-induced climate change The AR4 report had over 2,000 experts from 154 countries Risk assessment: is the climate changing? Risk management: how do we adapt and mitigate effects?

Third assessment The IPCC’s 2001 report showed Increasing information shows a warming world Humans are changing the atmosphere, which will affect climate We have increased confidence in models of future climate change Stronger evidence that most recent warming is human-caused Human influences will continue to change the atmosphere Temperature and sea levels are rising We need more information and understanding

A Nobel Effort The 2007 Nobel Peace Prize went to the IPCC and former Vice President Al Gore: the leading advocate of the need to take action on climate change For their efforts to disseminate knowledge about man-made climate change and to lay groundwork to counter it Gore also was awarded the Academy Award for his film An Inconvenient Truth

Climates in the past It is harder to find evidence of climate change the further into the past we search Records of temperature, precipitation, storms have been kept for only 100 years Since 1880, especially since 1976, our climate warmed Proxies: records providing information on climate Using temperature, ice cover, precipitation, tree rings, pollen, landscapes, marine sediments, corals, etc. Earth warmed from 1100 to 1300 A.D. Little Ice Age: 1400–1850

Ice cores Analyzing ice cores from Greenland and the Antarctic shows global climate can change within decades Uses CO2 and CH4 (methane) and isotopes of O and H Climate oscillates between ice ages and warm periods Ice ages tie up water in glaciers, lowering sea levels 8 glacial periods occurred over the past 800,000 years Ice ages have lower GHGs and temperatures CO2 levels ranged between 150 and 280 ppm Milanovitch cycles: climate oscillations due to Earth’s orbit Periodic intervals of 100,000, 41,000, and 23,000 years

Rapid changes Rapid climatic fluctuations during glaciation and warmer times The Younger Dryas event: 11,700 years ago Dryas: a genus of arctic flower Arctic temperatures rose 7ºC in 50 years Caused enormous impact on living systems Warming was not caused by changing solar output

Oceans and climate Oceans play a dominant role in determining climate They are a major source of water and heat Evaporation: supplies water vapor to the atmosphere Condensation: supplies heat to the atmosphere Heat capacity: oceans absorb energy with heated water Oceans convey heat through currents Thermohaline circulation pattern: the effects of temperature and salinity on the density of seawater This giant, complex conveyor belt moves water from the surface to deep oceans and back

The oceanic conveyor system

Thermohaline circulation affects climate The movement of warm water toward the North Atlantic transfers enormous amounts of heat toward Europe, providing a much warmer than expected climate The circulation pattern cycles over 1,000 years It is vital to maintaining current climate conditions In the past, the conveyor system has been interrupted Abruptly changing the climate Large amounts of fresh water lower water’s density Preventing the sinking of surface waters Slowing the northern movement of warmer, saltier water

Heinrich events Heinrich events: fresh water from melting icebergs from the polar ice cap dilutes salt water Six times in the past 75,000 years Diluted water doesn’t sink The conveyor system is shifted southward to Bermuda (instead of Greenland) The climate cools in a few decades Return of the normal pattern abruptly warms the climate The Younger Dryas event involved dammed-up water from glacial Lake Agassiz entering the St. Lawrence

What if …? Extended global warming will Increase precipitation over the North Atlantic Melt sea ice and ice caps The conveyor will decrease over the 21st century The Achilles’ heel of our climate system: weakening of the conveyor and a changed climate Especially in the northern latitudes

The Earth as a greenhouse Factors that influence climate Internal components: oceans, atmosphere, snow, ice External factors: solar radiation, Earth’s rotation and orbit, gaseous makeup of the atmosphere Radiative forcing: the influence of any factor on the energy balance of the atmosphere-ocean-land system Positive (negative) forcing: leads to warming (cooling) Forcing is measured in Watts/m2 Solar radiation entering the atmosphere = 340 W/m2 Radiation is acted on by forcing factors

Warming processes Greenhouse gases (GHGs): water vapor, CO2, other gases Light energy goes through the atmosphere to Earth Earth absorbs and converts energy to heat Infrared heat energy radiates back to space GHGs (but not N2 and O2) in the troposphere absorb some infrared radiation Direct it back to Earth’s surface The greenhouse effect was first recognized in 1827 It is now firmly established

GHGs insulate Earth GHGs delay the loss of infrared heat (energy) Without insulation, Earth would be -19°C instead of +14°C Life would be impossible Earth’s global climate depends on the concentration of GHGs Changing amounts of GHGs change positive forcing agents, which would change the climate Tropospheric ozone has a positive forcing effect Varying with time and location

The greenhouse effect

Snow and ice contribute to albedo by reflecting sunlight Cooling processes Planetary albedo: sunlight reflected by clouds Contributes to overall cooling by preventing warming Low-flying clouds have a negative forcing effect High-flying, wispy clouds have a positive forcing effect Absorb solar radiation and emit infrared radiation Snow and ice contribute to albedo by reflecting sunlight

Volcanoes and aerosols Volcanic activity can lead to planetary cooling Reflects radiation from particles and aerosols Aerosols: microscopic liquid or solid particles from land or water Industrial aerosols (pollution) cancel some GHG warming Sulfates, nitrates, dust, soot from industry and forest fires Sooty aerosols (from fires): warming effect Reduced pollution in the U.S. and Europe decreased aerosols China’s and India’s pollution has increased aerosols

Global warming and cooling

Solar variability Variation in the Sun’s radiation influences the climate Changes in solar radiation occur on 11-year cycles Solar radiation increases during high sunspot activity Sunspots block cosmic ray intensity Solar output declined in 1985 and continued for 20 years But global temperatures rose rapidly The IPCC AR4 concluded that GHGs were 13 times more responsible for warming temperatures than solar changes

Thus … Global atmospheric temperatures are a balance between positive and negative forcing from natural causes (volcanoes, clouds, natural GHGs, solar irradiance) and forcing from anthropogenic causes (sulfate aerosols, soot, ozone, increased GHGs) Forcing agents result in climate fluctuations It is hard to say any one event or extreme season is due to humans But climate has shifted enough to generate international attention

Evidence of climate change Weather varies naturally year to year Local temperatures may not follow global averages But the 10 warmest years on record were 1997–2008 2005 set a record high—the warmest since the late 1800s The average global temperature has risen 0.6°C since the mid-1970s (0.2°C/decade) Warming is happening everywhere Most rapidly at high latitudes of the Northern Hemisphere The warming is a consequence of an “enhanced greenhouse effect”

Ocean warming Recently, the upper 3,000 meters of the ocean have warmed Dwarfing warming of the atmosphere 90% of the heat increase of Earth’s systems Over the last decade, oceans have absorbed most of the non-atmospheric heat A long-term consequence: the impact of this stored heat as it comes into equilibrium with the atmosphere It will increase atmospheric and land heat even more A short-term consequence: unprecedented rising sea levels Thermal expansion and melting glaciers and ice caps

The rise in global mean sea level

Other observed changes by the IPCC AR4 Changes are consistent with GHG-caused climate change Increased warm temperature extremes Decreased cold temperature extremes Spring comes earlier, fall later, in the Northern Hemisphere Ecosystems are out of sync Tree deaths and insect damage Heat waves are increasing in intensity and frequency Droughts are increasing in intensity and frequency 60% of the U.S. is in a drought that started in the 1990s

More changes reported by the IPCC Rising Arctic temperatures have caused major shrinkage of Arctic sea ice (11.7% in 10 years) Alaska, Siberia, Canada have warmed 5°F in summer, 10°F in winter Spring comes 2 weeks earlier than 10 years ago The polar ice cap has lost 20% of its volume in 20 years Permafrost is melting Unprecedented melting of the Greenland Ice Sheet can raise ocean levels 23 feet

Decline of Arctic sea ice

Other changes reported by the IPCC Antarctica temperatures have risen 0.5°–0.85°C The West Antarctic Ice Sheet (WAIS) is shrinking and can raise sea levels by 16–20 feet Accelerating glacier melting since 1990 Changing patterns of precipitation and flooding Greater amounts from 30° N and S poleward More intense and frequent tropical hurricanes Marine fish populations have shifted northward Ocean acidification: decreased pH due to CO2 absorption The surface ocean’s chemistry is actually changing

Carbon dioxide levels CO2 levels oscillate 5–7 ppm, reflecting seasonal changes in photosynthesis and respiration Fall through spring: respiration increases CO2 levels Spring through fall: photosynthesis decreases CO2 By 2009, atmospheric CO2 levels = 338 ppm 39% higher than before the Industrial Revolution Higher than in the past 800,000 years Fossil fuels increase CO2 levels 1 kg of fossil fuel burned releases 3 kg CO2 Eight billion tons (gigatons, Gt) of fossil fuel carbon/year

Sources of carbon dioxide Half of fossil fuel carbon comes from industrialized nations Burning forests Over the past 50 years, release of carbon has tripled Half of the carbon is removed by sinks Sinks: burning fossil fuels should add 8 GtC/year to the air But only 3.3 GtC/year are actually added Carbon sinks (the ocean, biota) absorb CO2 Oceans take up CO2 by phytoplankton or undersaturation But there are limitations to uptake Forests are valuable for their ability to sequester carbon

Sources of carbon dioxide emissions from fossil fuels

Other gases Other gases absorb infrared radiation Adding to the insulating effect of carbon dioxide Most are anthropogenic sources and are increasing Water vapor: the most abundant GHG Its tropospheric concentration varies, but is rising Higher temperatures increase evaporation and water vapor (humidity) Higher humidity traps more heat, causing more warming (positive feedback)

Other GHGs Methane: 20 times more effective than CO2 in heating From microbial fermentation (in wetlands), green plants Two-thirds of emissions are from human sources: livestock, landfills, coal mines, natural gas, rice cultivation, manure Rising at 0.8 ppb/year, it is more abundant than in the past 800,000 years Nitrous oxide: has increased 18% over the last 200 years From agriculture, oceans, biomass burning, fossil fuel burning, industry, anaerobic denitrification (fertilizers) Warms the troposphere and destroys stratospheric ozone

Ozone and CFCs Ozone: a short-lived but potent GHG in the troposphere From sunlight acting on pollutants Has increased 36% since 1750 From traffic, forest fires, agricultural wastes CFC and other halocarbons Long-lived GHGs causing warming and ozone destruction From refrigerants, solvents, fire retardants They absorb 10,000 times more infrared energy than CO2 Levels are slowly declining but will remain for decades

Future changes in climate Happening now: higher temperatures, rising seas, heat waves, droughts, intense storms, season shifts, melting ice GHG levels are rising Along with fossil fuel demand and population Emissions will rise 35% (2030) and 100% (2050) Modeling global climate: computing power has increased Can explore the potential future impacts of rising GHGs Atmospheric-ocean general circulation models (AOGCMs) Simulate long-term climatic conditions

Significant findings of climate models Equilibrium climate sensitivity: if atmospheric CO2 stays at 550 ppm (double preindustrial values), temperature will rise 3°C (2°–4.5°C) by 2050 Higher latitudes and continental interiors will warm most But it will be warmer everywhere Snow cover and sea ice will decrease, opening up the Arctic Ocean by 2100 Shrinking glaciers and ice caps will increase sea levels 90% of upper permafrost will thaw

More findings Warmer, dilute upper layers of the North Atlantic Ocean will lead to decreased (but not collapsed) thermohaline circulation Increased storm intensities, higher wind speeds and waves, more intense precipitation More frequent, longer-lasting heat waves Longer growing seasons, shorter frost days Dry areas will get dryer, wet areas will get wetter Extreme droughts will affect up to 30% of the world Ecosystems (polar ecosystems, coral reefs, rainforests) will be profoundly affected, increasing species extinctions

What about the Antarctic? The Antarctic could be a huge factor in rising sea levels Greenland and Antarctic ice sheets hold enough water to raise sea levels 230 feet Snowfall has not changed in the past 50 years 87% of the 244 glaciers are melting The melting ice sheet is raising sea levels 0.4 mm/year Higher continental temperatures (3°C) Models project a 5% snowfall increase for each 1°C temperature rise

Climate change in the U.S. All impacts are expected to continue and/or increase Impacts are greater in Alaska than any other U.S. region Changes in the U.S. over the past 50–100 years include Average temperature has risen 2°F Wetter areas are wetter, dryer areas are dryer Heavy downpours and storms have increased More extreme and frequent weather events Stronger Atlantic hurricanes Arctic sea ice is declining rapidly

Response to climate change Industries and transportation network are locked into using fossil fuels Massive emissions of GHGs will continue Adaptation: anticipate harm and plan adaptive responses to decrease vulnerability of people, property, and the biosphere Mitigation: take action to prevent emissions Skeptics about global warming exist Fossil fuel industry, Rush Limbaugh, conservative think tanks, some scientists