In physical terms, human activities are adding energy to the ocean-atmosphere interface. This is a highly non-linear system where a small input pertubation could produce a large, an unpredictable output result.

What might some of these outputs be?

Important new diagnostic

20,000 years of change since the last ice age, 2/3 of the West Anarctic Ice Sheet has been lost and this has raised sea level by 10 meters.

What a difference 104 years makes

1900 Image

2004 Image

More glacial comparisons

Glacier Benchmarks

The earth has a natural greenhouse effect due to trace amounts of H₂0 and CO₂ that naturally occur. The enhanced greenhouse effect refers to the augmentation of these natural gases by human activities.

What's the evidence?

• World wide Coral Bleaching
• Warming of the oceans
• Rapid Retreat of tropical glaciers

The energy balance in the atmosphere is shown here:

So clearly, if human activities increase the ability for the earth's atmosphere to absorb IR radiation, this produces a net warming of the atmosphere over time. This is the Enhanced Greenhouse effect:

 

Table 1

Characteristics of some major (climate changing) greenhouse gases

Greenhouse gas	Sources	Sinks	Importance for climate
Carbon Dioxide (CO2)	1) Burning of fossil fuel 2) Land-use change (deforestation)	1) Ocean Uptake 2) Plants!& photosynthesis	Absorbs infrared radiation; affects stratospheric O3
Methane (CH4)	1) Biomass burning 2) Enteric fermentation 3)Rice paddies	1) Reactions with OH 2) Microorganisms uptake by soils	Absorbs infrared radiation; affects tropospheric O3 and OH; affects stratospheric O3 and H2O; produces CO2
Nitrous Oxide (N2O)	1) Biomass burning 2) Fossil-fuel combustion 3) Fertilizers	1) Removal by soils 2) Stratospheric photolysis and reaction with O	Absorbs infrared radiation; affects stratospheric O3
Ozone (O3)	Photochemical reactions involving O2	Catalytic chemical reactions involving NOx, ClOx and HOx species.	Absorbs ultraviolet and infrared radiation
Carbon Monoxide (CO)	1) Plant emissions 2) Man-made release (transport, industrial)	1) Soil uptake 2) Reactions with OH	Affects stratospheric O3 and OH cycles; produces CO2
Chlorofluorocarbons (CFCs)	Industrial production	Insignificant in troposphere, dissociated in stratosphere (photolysis and reaction with O)	Absorbs infrared radiation; affects stratospheric O3
Sulphur Dioxide (SO2)	1) Volcanoes 2) Coal and Biomass burning	1) Dry and wet deposition 2) Reactions with OH	Forms aerosols, which scatter solar radiation

Concentration increases since 1750:

• Carbon Dioxide: 280 ppm 375 ppm (29%)

  But Beware

• Nitrous Oxides: 280 ppb 360 ppb (11%)
• Methane: 0.70 ppm - 1.70 ppm (143%)

• In principle, CFCS are very bad and will dominate the greenhouse gases in our atmosphere if their terrestrial usage remains high. CFC worldwide production, however, has been significantly reduced because of concern about The Ozone Layer depletion.

• Methane is more directly related to food production and population growth so it could also dominate in the near future

• Frozen methane is also found in the Arctic Ice Caps and will be released due to global warming thus exacerbating the problem. This is far more serious that people realize or has been reported.

Data showing the increasing concentration of Greenhouse Gases:

CO₂ is steadily increasing at the rate of about 1.5 ppm per year

NO_x is leveling off due to pollution abatement on vehicles but this is offset by increasing vehicular traffic

CH₄ is only recently been measured. Rate of increase is about 10 ppb per year. However, since 1 CH₄ molecule is worth 25 CO₂ molecules, the equivalent growth rate in terms of CO₂ is 2.5 ppm. Thus methane may eventually be the dominant enhanced greenhouse gas in our atmosphere. What can we do about this?

Global Warming: Is it Real?

Rise in Atmospheric CO₂:

This is not controversial:

Recent Measurements (on going monitoring)

Recent Ice Core Data

Land Use Changes:

Okay, so now we have a pretty strong indication that atmospheric CO₂ is building up over time. Are there indications that this is leading to a warmer planet? (This is the nature of your first assignement)

Again, here is some data:

Tempeature profiles by Month

Predicting the Future very difficult

But the past is an interesting guide:

The data which convinced the scientific community (1999):

Temperature record for the last 2000 years

When positional data is combined with temperature data and timesliced in this way - it seems clear the Global Warming is occurring. This conclusion was reached by a National Academcy of Science panel in Sept. 1995 and is accepted by most.

Some evidence for warming in the 1920's: Maybe Natural:

This was followed by mid-century cooling, again thought to be natural:

Which was then following by likely human induced warming:

Since 2000, clearly there is systematic world wide warming:

2001
2002
2003
2004
2005

The Best Visualization to Date

Animated Sequence for Summer Months

Animated Sequence for Winter Months

Now try and convince congress!