Everybody talks about climate, we, too!
The climate system of the Earth is highly complex. Originally, climate was defined as the mean state of the atmosphere. However, the atmosphere is strongly influenced by other components of the climate system, such as the ocean, the cryosphere (the ice and snow on Earth) and the biosphere. In particular, the ocean plays an important role in the climate system since it reacts very slowly to temperature changes in the atmosphere.
Why did we have ice ages and warm periods?
How long did they last?
How cold was it during an ice age?
What happened when it ended?
Not all of these questions can we answer already.
In order to be able to say anything about the future climate, we first have to fully understand the present climate system. The climate of the past gives valuable hints here. But how do we know about the climate of the past? Meteorological measurements did not exist until about 200 years ago. Nevertheless we talk about ice ages 100.000s of years ago!
A valuable source of information about the paleoclimate (climate of the past) are ice cores from the large ice sheets of Greenland and Antarctica. The climate of the past is stored in these ice sheets that are several kilometers thick. Such an ice core has a diameter of about 10cm and can be up to 3km long!
We can measure various phyical and chemical properties of the ice cores that give us information about the former climate. Additionally, the air bubbles in the ice contain very old air. So we can learn about the constitution of the atmosphere at the time the ice was formed. The oldest ice we have found so far is 800.000yrs old! So we know the concentration of CO2, methane or other greenhouse gases in the atmoshere at that time. This information is found ONLY in the ice cores, in no other climate archive!
Here is how we get the temperature information from an ice core: