No matter where we are on Earth, we can observe changes in vegetation. Some changes are drastic, such as going from dormant to full growth during a temperate winter.
Vegetative growth is dependent on both surface temperature (which influences soil temperature) and precipitation (which influences soil moisture). Together these environmental variables help determine the beginning, duration, and end of the growing season; the latter marked by leaf senescence, when leaves of deciduous trees die and turn colors.
How do archaeologists learn about climatic conditions and their effects on people in the past? In 1815, Mount Tambora in Indonesia erupted so violently that the sound of the eruption could be heard 1,600 miles away. Gases from the volcano shot into the stratosphere almost six miles above the Earth’s surface and lingered for years. Sulfur dioxide combined with water molecules to form sulfate particles that reflected sunlight away from Earth, gradually causing the planet’s surface to cool. The colder temperatures caused severe weather events worldwide.
Climate scientists study evidence in the geologic record, such as fossils, to figure out what climate was like over hundreds of thousands of years (“paleoclimate”). One fossil they use is pollen, a part of a flowering plant that helps make a seed. Pollen can be blown into lakes, where it is preserved in sediment. Pollen from spruces, which do well in cold climates, can suggest what climate was like when spruce pollen was deposited.