Answer to Question 1
Carbon dioxide is increasing mostly because of the burning of fossil fuels. Fossil fuels consist of carbon or compounds where carbon and hydrogen are bound together. When burned, the bonds between carbon atoms or between carbon and hydrogen atoms are broken, and then the carbon bonds with oxygen in the air to form carbon dioxide. Most of the historic methane increase is attributed to agricultural activities such as the decay of organic matter in rice paddies and the digestion of cows and sheep.
Answer to Question 2
Incoming solar energy varied with the 11-year sunspot cycle but has also shown an overall slight increase since 1850, which is a natural contribution to long-term warming.
Greenhouse-gas concentrations have increased dramatically since 1850 and especially since 1960. Most of this increase relates to human consumption of fossil fuels. Increasing concentration of greenhouse gases causes warming.
An increase in albedo due to more clouds and pollution haze in the atmosphere causes the reflection of more incoming heat energy back into space. Changing land-use as natural vegetation is replaced with agriculture and urban areas also increases albedo. These changes have both natural and human-caused components and cause cooling.
Volcanic eruptions release sulfurous aerosols into the atmosphere that strongly absorb incoming solar radiation and are natural causes of cooling. Although the effect is dramatic on periods of years, it is not long lasting, so there has been no overall trend in the last 150 years.
Lightning on Earth
The four processes of pharmacokinetics: absorption, distribution, metabolism, and excretion
Earth’s Revolution and Rotation: The Causes of Earth’s Seasons
Catabolic and anabolic processes in anaerobic carbohydrate metabolism
carbon cycle
Estimates of carbon stored in the plants and soils of different ecosystems.