Science, Technology and the Environment (SC NATS 1840A) –
Tuesday, November 27 , 2012 th
Reading chapter 21.1
How has climate changed in recent and distant past?
How have carbon dioxide concentrations and temperature changed?
Can evidence for a causal link be found?
Are changes observed today historically unusual/significant?
If not, then perhaps a natural climate variation?
Even a natural variation could threaten our ability to sustain ourselves;
If changes are unprecedented, then more reason to believe human activities are the
The study of past climate is called paleoclimatology
Reconstructing Past Climate:
How can we determine CO co2centrations and temperatures from one million years ago?
Ice Cores: Long cylinders of packed ice obtained by drilling vertically down using a hollow drill
Core samples extracted in 4-6m segments – one core (Vostok) is almost 4km long!
As snow builds up, it becomes compressed and turns to solid ice. Each season is seen as a distinct layer
in a core.
A 2.5 km long core represents a 400,000 year record of climate on Earth – it contains numerous proxies.
Isotope ratios are a proxy for temperature;
Small gas bubbles are samples of past atmosphere;
Impurities and dust reveal pollution;
Ice core records are general regarded as reliable
The Story told by Ice Cores
CO 2as varied in range 200-300 ppm;
Temperature has averaged 3 degrees colder than today;
There have been three ice ages in past 160,000 years.
Ice cores do not tell us whether temperature increases follow CO2or vice-versa. We are currently in an inter-glacial period. Last ice age ended around time that humans began farming.
Temperature of past 10,000 years has been slightly colder than today. Carbon dioxide concentrations
have been in the 260-280 ppm range.
Past 200 years: steadily increasing CO2concentration, and slowly rising temperature.
We have been emerging from a colder period (1600-1850) usually called “little ice age”.
Clearly some connection between temperature and CO but w2ich leads the other remains unclear.
Carbon dioxide record is unambiguous; different temperature series in close agreement.
Ground: +0.16 C/decade. Satellite: +0.13 C/decade
Global Warming is caused by an enhanced greenhouse effect, the result of rising atmospheric
concentrations of greenhouse gases
1. Carbon dioxide concentrations are higher now than at any time in the past 400,000 years.
2. Average temperatures today are slightly below peaks observed in several past inter-glacial phases.
3. Carbon dioxide concentration and global temperature changes are linked. Current trends could lead
to further changes in climate
Strength of link remains uncertain.
How strong are different feedback mechanisms?