Global warming and carbon dioxide

What is the greenhouse effect?

You know that air inside a car can heat up to a temperature greater than the surrounding atmosphere when sun shines. Automotive glass lets light (energy) in, but does not let heat (energy) out.

Carbon-dioxide in Earth's atmosphere acts the same way as the glass, trapping solar energy. This is a good thing! Without any carbon dioxide in the Earth's atmosphere, scientists estimate the temperature on Earth's surface would be about 60 F cooler than it is

So what is the concern about global warming?

The concern is that human activities have been adding carbon dioxide to the atmosphere at a rate which is likely to cause very rapid warming: too fast for for many species on earth to adapt, and possibly too fast for human societies to adapt.

Carbon in the atmosphere

Here is the composition of the *dry* atmosphere (not including water).

Water (water vapor) makes up about 0.4% (globally)--typically 1-4% at the surface.

Relatively speaking, the amount of carbon in atmosphere is not very much. It's mainly present as

  • $CO_2$ - Carbon dioxide
  • $CH_4$ - Methane ("natural gas")

How do we know how much $CO_2$ there is in the atmosphere?

If you want to get an idea of worldwide concentrations of $CO_2$ over long periods of time... is a city a good place to build a place to measure $CO_2$ concentrations in the atmosphere? In the midst of a rain forest?

The Mauna Loa observatory is located on an extinct volcano on one of the Hawaian islands, in the middle of the Pacific Ocean.

They've been making measurements of $CO_2$ since the 1950s:


How long has this increase in $CO_2$ been going on?

How do we know atmosphere composition and temperature in the distant past?

Tree rings (thickness and density) depend on temperature and go back ~11,000 yr. (Temperatures)

Ice cores preserve air samples back about 650,000 yr. (CO2 levels)

Temperature affects the ratio of O16 to O18. (Temperatures)

Carbon-dioxide levels

What happened around 1800? The graph at the right shows that consumption of coal took off at around the time that atmospheric carbon-dioxide really took off.


(MacKay)

Are human activities changing the atmosphere?

The graph above suggests that the increase got started in the 1700s or 1800s. This was the time when the industrial revolution began: People in England realized that machines, powered by the energy from burning coal, could do a lot of jobs for us.

Coal is almost pure carbon. The chemical reaction that takes place when you burn it with oxygen from the atmosphere is: $$C+O_2 \to CO_2$$ This reaction gives off 1.8 calories per gram of carbon dioxide produced.

More recently, folks are burning natural gas (methane) like this: $$CH_4+2O_2\to CO_2 + 2H_2O$$ which gives off 4.8 calories per gram of carbon dioxide.

The IPCC

The Intergovernmental Panel on Climate Change (ipcc.ch)

  • has been commissioned by the UN and the World Meteorological Association to assess the status of climate change.
  • It consists of 100s of scientists, diplomats, and politicians, and attempts to reach consensus among these folks in regular reports.
  • Received the Nobel Peace Prize (2007) along with Al Gore.

Their measured consensus is that

  • There has been an increase in world temperatures of approximately 1${}^o$F (0.5 C) since 1957,
  • which, with a likelihood of 90% is due to human activity rather than being a natural effect.

What about natural variation?

Temperature record for the last two millenia.

The concern is not so much because of the 0.5 C ($1{}^o$F) temperature change *so far*, but rather the possibility of a further 4-6 C rise in the next 100 years.

Not just warming...

One way that carbon dioxide leaves the atmosphere (phew!) is it dissolves in water.

But, when carbon-dioxide dissolves in water, the water becomes more acidic.

Coral reefs are largely made of calcium carbonate skeletons of corals. But acidity increases the amount of calcium carbonate that can dissolve in water.


What can be done?

Implementing all of these suggestions would reduce U.S. carbon-dioxide emissions by 50%:

But how do we change these ways of doing things?