Climate change is supported by evidence from temperature records, pollen grains in peat bogs and tree rings.
Some go back 2 or 3 centuries – long-term data can be recorded with thermometers.
Pollen grains are well preserved in the acidic and anaerobic conditions of peat bogs. It is useful for reconstructing past environments because they are resistant to decay, easy to identify as each plant species produces distinct pollen and each has best conditions to survive in. Peat forms in layers and carbon dating allows the age of each to be established.
Tree rings are used because every year new xylem vessels are formed by division of cells underneath the bark. The diameter depends on the season (wide in spring, narrow in summer). The rings can be clearly seen when the tree is cut, with a ring for each year of the growth.