The Maldives:

Rising seas may flood the Maldives• Island paradise• Rising seas due to global climate change

could submerge them– Erode beaches, cause

flooding– Damage coral reefs– Contaminate fresh water

• Residents have evacuated the lowest-lying islands

What is climate change?• Climate change is the fastest-developing area of

environmental science

• Climate = an area’s long-term atmospheric conditions– Temperature, moisture, wind, precipitation, etc. – Weather = short-term conditions at localized sites

• Global climate change = describes trends and variations in Earth’s climate– Temperature, precipitation, storm frequency

• Global warming and climate change are not the same

Global warming• Global warming = an increase in Earth’s average

temperature– Only one aspect of climate change

• Climate change and global warming refer to current trends– Earth’s climate has varied naturally through time

• The current rapid climatic changes are due to humans– Fossil fuels and deforestation

The sun and atmosphere keep Earth warm

• Four factors exert most influence on climate:

• The sun = without it, Earth would be dark and frozen– Supplies most of Earth’s energy

• The atmosphere = without it, Earth’s temperature would be much colder

• The oceans = shape climate by storing and transporting heat and moisture

• How Earth spins, tilts, and moves through space influences how the climate varies over long periods of time

The fate of solar radiation• The atmosphere, land, ice, and water absorb 70% of

incoming solar radiation – 30% is reflected back

Greenhouse gases warm the lower atmosphere

• Earth’s surface absorbs solar radiation, warms up, and emits infrared radiation

• Greenhouse gases = atmospheric gases that absorb infrared radiation– Water vapor, ozone, carbon dioxide, nitrous oxide, methane,

halocarbons [chlorofluorocarbons (CFCs)]

• Greenhouse gases then re-emit infrared energy, to earth and space

• Greenhouse effect = greenhouse gases keeping the surface

warm

The greenhouse effect is natural• Greenhouse gases have always been in the

atmosphere

• We are not worried about the natural greenhouse effect (we need it)– Anthropogenic increase is worrisome

Carbon dioxide is of primary concern

• It is not the most potent greenhouse gas, but there is a lot of it– The major contributor to the greenhouse effect

• CO2 exerts six times more impact than methane, nitrous oxide, and halocarbons combined

What caused levels of CO2 to increase?• Burning fossil fuels moves CO2 from lithospheric

stores into the atmosphere – The main reason for increased atmospheric CO2

• Deforestation contributes to rising atmospheric CO2– Forests serve as reservoirs for carbon– Removing trees reduces the carbon dioxide absorbed

from the atmosphere

• Humans have increased atmospheric CO2 from 280 parts per million (ppm) to 389 ppm– The highest levels in more than 800,000 years– OMG right?

Fluxes of carbon dioxide

Other greenhouse gases add to warming• Methane = fossil fuels, livestock, landfills, crops (rice)

• Nitrous oxide = feedlots, chemical manufacturing plants, auto emissions, and synthetic nitrogen fertilizers

• Ozone levels have risen 36% due to photochemical smog

• Halocarbon gases (CFCs) are declining due to the Montreal Protocol

• Water vapor = the most abundant greenhouse gas – Contributes most to the natural greenhouse effect– Concentrations have not changed

U.S. emissions of major greenhouse gases

Feedback complicates our predictions

• Tropospheric warming will transfer more water to the air– But the effects are uncertain

• A positive feedback loop? = more water vapor … more warming … more evaporation … more water vapor …

• A negative feedback loop? = more water vapor … more clouds … shade and cool Earth

• Minor modifications of the atmosphere could lead to major effects on climate

Most aerosols exert a cooling effect

• Aerosols = microscopic droplets and particles – Can have either a warming or a cooling effect

• Soot (black carbon aerosols) causes warming by absorbing solar energy

– Most tropospheric aerosols cool the atmosphere by reflecting the sun’s rays

Milankovitch cycles influence climate• Milankovitch cycles =

periodic changes in Earth’s rotation and orbit around the sun– Alter the way solar radiation is

distributed over Earth

• Modify patterns of atmospheric heating– Triggering climate variation – For example, periods of cold

glaciation and warm interglacial times

Solar output and ocean absorption influence climate

• Solar output = the sun varies in the radiation it emits– Variation in solar energy (e.g., solar flares) has not been

great enough to change Earth’s temperature

• Ocean absorption = the ocean holds 50 times more carbon than the atmosphere – Slowing global warming but not preventing it

• Warmer oceans absorb less CO2 – A positive feedback effect that accelerates warming

• Proxy indicators = indirect evidence

• Ice caps, ice sheets, and glaciers:- Trapped bubbles in ice cores provide a timescale of:

- Atmospheric composition, greenhouse gas concentrations, temperature trends

- Snowfall, solar activity, and frequency of fires

Proxy indicators tell us about the past

Ice cores from Antarctica

• Ice cores let us go back in time 800,000 years

More proxy indicators• Cores in sediment beds preserve pollen grains and other

plant remnants

• Tree rings indicate age, precipitation, droughts, and fire history

• In arid regions, packrats carry seeds and plants to their middens (dens)– Plant parts can be preserved for centuries

• Researchers gather data on past ocean conditions from coral reefs

• Scientists combine multiple records to get a global perspective

Models help us predict the future• Climate models = programs

combine what is known about:– Atmospheric and ocean

circulation – Atmosphere–ocean

interactions– Feedback mechanisms – Etc...

Models simulate climate processes to predict climate change

The State of the Art in Modeling the Climate (2005)

Global Climate Global Climate ModelsModels

Results from three simulations

• Figure (a) shows natural climate factors only

• Figure (b) shows only human factors– Greenhouse gas emissions

• Figure (c) shows both factors

• (Red line is observed climate data)

Current and future trends and impacts• Evidence that climate conditions have changed since

industrialization is everywhere– Fishermen in the Maldives, ranchers in Texas, homeowners in

Florida, etc.

• Scientific evidence that climate has changed is overwhelming and indisputable

• Intergovernmental Panel on Climate Change (IPCC) was established in 1988– Composed of hundreds of international scientists and

government officials

The IPCC’s fourth assessment report (2007)

• The IPCC reports on the synthesis of scientific information concerning climate change• Global consensus of scientific climate research• Summarized thousands of studies

• Evidence is overwhelming

Temperatures continue to increase• Average surface temperatures increased 0.74 °C

since 1906– Most of the increase occurred in the last few decades– Number of extremely hot days have increased– The 16 warmest years on record have been since 1990

The future will be hotter

• In the next 20 years, temperatures will rise 0.4°C

• At the end of the 21st century, temperatures will be 1.8–4.0 °C higher than today’s• We will have more unusually hot days and heat waves

• Polar areas will have the most intense warming

• Sea surface temperatures will rise• Hurricanes and tropical storms will increase in power and

duration

Temperatures will rise globally

Projected increases in surface temperature for 2090–2099 relative to 1980–1999

Precipitation is changing, too

• Some regions are receiving more precipitation than usual, and others are receiving less

• Droughts have become more frequent and severe– Harming agriculture, increasing soil erosion,

reducing water supplies, and triggering fires

• Heavy rains contribute to flooding– Killing people, destroying homes, and inflicting

billions of dollars in damage

Projected changes in precipitation

Precipitation will increase at high latitudes and decrease at low and middle latitudes

Figure SPM.7

Relative changes in precipitation (in percent) for the period 2090–2099, relative to 1980–1999. Values are multi-model averages based on the SRES A1B scenario for December to February (left) and June to August (right). White areas are where less than 66% of the models agree in the sign of the change and stippled areas are where more than 90% of the models agree in the sign of the change. {Figure 10.9}

Melting snow and ice• Glaciers are disappearing– Glaciers on tropical mountaintops have disappeared– The remaining 26 of 150 glaciers in Glacier National Park will be

gone by 2020 or 2030– Reducing summertime water supplies

• Melting of Greenland’s Arctic ice sheet is accelerating

• Warmer water is melting Antarctic coastal ice shelves– Interior snow is increasing due to more precipitation

• Melting ice exposes darker, less-reflective surfaces, which absorb more sunlight, causing more melting

2007 vs 2005

Melting ice...• Nations are rushing to exploit underwater oil and mineral

resources made available by newly opened shipping lanes• Permafrost (permanently frozen ground) is thawing– Destabilizing soil, buildings, etc. and releasing methane

http://www.worldviewofglobalwarming.org/pages/glaciers.html

Rising sea levels• Runoff from melting glaciers and ice will cause

sea levels to rise • As oceans warm, they expand– Leading to beach erosion, coastal floods, and

intrusion of salt water into aquifers

Coastal areas will flood

• Storm surge = temporary, localized rise in sea level– Caused by the high tides and winds of storms

• Cities will be flooded– 53% of people in the U.S. live in coastal areas

Rising sea levels will devastate coasts• 1 million acres of Louisiana’s wetlands are gone– Rising sea levels eat away vegetation– Dams upriver decrease siltation– Pollution from the Deepwater Horizon

• Millions of people will be displaced from coastal areas

Coral reefs are threatened• Coral reefs are habitat for food fish – Snorkeling and scuba diving sites for tourism

• Warmer waters contribute to coral bleaching– Which kills coral

• Increased CO2 is acidifying the ocean– Organisms can’t build their exoskeletons

• Oceans have already decreased by 0.1 pH unit– Enough to kill most coral reefs

Climate change affects organisms and ecosystems

• Organisms are adapted to their environments

• Global warming modifies temperature-dependent phenomena (e.g., timing of migration, breeding)

• Animals and plants will move toward the poles or upward in elevation– 20–30% of species will be threatened with extinction

• Droughts, fire, and disease will decrease plant growth

Animals and plants have nowhere to go• Animals and plants adopted to montane environments will

be forced uphill until there is no place to go

Climate change affects people• Societies are feeling the impacts of climate change

• Agriculture: shortened growing seasons, decreased production, crops more susceptible to droughts – Increasing hunger

• Forestry: increased fires, invasive species– Insect and disease outbreaks

• Health: heat waves and stress can cause death– Respiratory ailments, expansion of tropical diseases– Disease and sanitation problems from flooding– Drowning from storms

Climate change affects economics• Costs will outweigh benefits of climate change

• It will widen the gap between rich and poor– Those with less wealth and technology will suffer most

• External costs of damages will be $10–350/ton of carbon

• It will cost 1–5% GDP on average globally – Poor nations will lose more than rich ones

• The Stern Review predicts it will cost 5–20% of GDP by 2200– Investing 1% of GDP now could avoid these costs

Impacts will vary regionally• Where we live will determine how we experience the

impacts of climate change

• Temperature changes have been greatest near the poles– Melting ice sheets, thinning ice, increasing storms, etc.– Harder for people and polar bears to hunt

• U.S. temperatures will continue rising– Plant and animal communities will shift north and upward– More intense extreme weather events

• The southern U.S. will get drier, the northern wetter– Sea levels will rise and may be worse in the East

Impacts of climate change

The Arctic has suffered the most so far

U.S. temperatures will continue to rise

Impacts of climate change will vary

Are we responsible for climate change?

• Scientists agree that increased greenhouse gases are causing global warming– Burning fossil fuels is increasing greenhouse gases

• In 2005, scientists from 11 nations issued a joint statement urging political leaders to take action

• There is a broad and clear scientific consensus that climate change is a pressing issue– But many people deny what is happening

• People will admit the climate is changing– But doubt we are the cause

The debate over climate change is over

• Conservative think tanks and industry-sponsored scientists cast doubt on the scientific consensus

• The news media tries to present two sides to an issue– But the sides’ arguments are not equally supported

by evidence

• Most Americans accept that fossil fuel consumption is changing the planet

Electricity generation

• The largest source of U.S. CO2 emissions– 70% of electricity comes from fossil fuels– Coal causes 50% of emissions

• To reduce fossil fuel use: – Encourage conservation and efficiency– Switch to cleaner and renewable energy sources

A coal-fired, electricity-generating power plant

Conservation and efficiency

• We can make lifestyle choices to reduce electricity use– Use fewer greenhouse-gas-producing appliances– Use electricity more efficiently

Sources of electricity• We need to switch to clean energy sources– Nuclear power, biomass energy, solar, wind, etc.

• We need to consider how we use fossil fuels– Switching from coal to natural gas cuts emissions 50%– Cogeneration produces fewer emissions

• Carbon capture = removes CO2 from power plant emissions

• Carbon sequestration (storage) = storing carbon underground where it will not seep out– We can’t store enough CO2 to make a difference

Transportation• 2nd largest source of

U.S. greenhouse gases– Cars are inefficient

• Ways to help:– More efficient cars– Drive less and use

public transportation– Ride a bike!

U.S. public transportation saves 4.2 billion gallons of gasoline and 37 million metric tons of CO2 emissions per year

Conventional cars are inefficient

We can reduce emissions in other ways• Agriculture: sustainable land management lets soil store more

carbon• Reduce methane emissions from rice and cattle• Grow renewable biofuels

• Forestry: reforest cleared land, preserve existing forests• Store carbon in trees and soil

• Waste management: treating wastewater• Generating electricity by incinerating waste• Using the methane from landfills

• Individuals can recycle, compost, reduce, or reuse goods

We need to follow multiple strategies• There is no magic bullet for mitigating climate

change

Kyoto Protocol• International agreement to reduce

greenhouse gas emissions• NOT ratified by: USA, Afghanistan, Andorra,

and S. Sudan (Canada backed out)

States and cities are advancing policies• The U.S. federal government is not taking

action– State and local governments are

• By 2010, 1,000 mayors signed the U.S. Mayors Climate Protection Agreement – To meet or beat Kyoto Protocol guidelines

• California passed the Global Warming Solutions Act - To cut emissions 25% by 2020

• Regional Greenhouse Gas Initiative (RGGI) in 2007- 10 northeastern states - Set up a cap-and-trade program

You can reduce your carbon footprint

• People may apply many strategies to decrease their footprint

• YOU must help drive personal and societal changes needed to mitigate climate change

• Global climate change may be the biggest challenge facing us and our children – We can make a difference, remember the ozone!