Trees
Trees tell us about current and past climates worldwide. The mass of any single tree is made up primarily of carbon and water combined by solar energy through photosynthesis over time. By removing carbon dioxide from the atmosphere, trees and forests are carbon sinks. In many forests carbon may be stored for centuries. Deforestation and rainforest destruction is causing significant increases in greenhouse gas emissions. When trees and plants decompose and are buried, geological forces help generate carbon-based fossil fuels. When we burn these resources, carbon that was stored for thousands of years enters the atmosphere in a matter of minutes or hours.
Mountain tree lines
All organisms are adapted to ranges of temperature, precipitation, humidity, and sunlight. For example, trees in the Rocky Mountains typically do not grow above 10,000 feet because the climate is too harsh above that elevation. Climatic conditions and weather variations influence tree growth. The structure and density of tree-rings provide an estimate of temperature and precipitation during growth periods.
Based on evidence from tree rings and other natural records around the world, scientists know that the average temperature on Earth is warmer than it has been for at least the past 1,300 years.
Glacial Retreat
Global warming has led to glacial retreat. Some glaciers have already melted into lakes while the existence of a great number of glaciers worldwide is threatened by global warming.
Glacial retreat affects the availability of fresh water for billions of people around the world.
Melting of ice sheets and glaciers, combined with the thermal expansion of seawater as the oceans warm, is also causing sea level to rise.
Polar Bears
Changes in climate conditions can affect the health and function of ecosystems and the survival of entire species.
Polar Bears that thrive on frozen water in the arctic have become significantly challenged by melting sea ice. Polar bears were the first creatures to be added to the endangered species list and threatened with extinction due to human-induced climate change.
The Interaction of Life and Climate
Our oxygen rich atmosphere evolved over geologic time as a result of plant life capturing and converting energy from the sun. Water vapor, the most abundant greenhouse gas, traps heat and enables life on Earth. Human activities such as burning fossil fuels and reducing forest cover has resulted in increases in atmospheric carbon dioxide which is gradually warming our planet and changing the balance of the climate system. The interconnectedness of systems on Earth means that a change in one component of the climate system can influence the equilibrium of the entire Earth system. Fossil records show that changes in environmental conditions affects the survival of individual organisms and entire species. Organisms exposed to climate conditions outside their normal range must adapt, migrate, or perish.