The Carbon Cycle
As atmospheric concentrations of carbon dioxide continue to increase, the Earth's climate is expected to change significantly over the next several decades. In response, scientists expect to see gradual shifts in the regional distribution of plant species. Moreover, there is speculation that rising temperatures and heightened carbon dioxide levels will accelerate the photosynthesis and growth rates of plants. Less well known is the critical role that vegetation will play in the carbon cycle and global warming. Scientists have carefully scrutinized and compared the amount of carbon dioxide released by fossil fuel burning to the rate of carbon dioxide buildup in the atmosphere and the amount absorbed by the oceans and vegetated land surfaces. They have concluded that over the past 15 years, approximately one-quarter of industrial carbon dioxide emissions have been absorbed and stored by the vast vegetated areas of the Northern Hemisphere, primarily the boreal and temperate forests of North America and Eurasia.

Normally, vegetation takes in carbon dioxide from the atmosphere and combines it with water to produce simple carbon compounds. This process, known as photosynthesis, is the basic biological process that powers the biosphere by removing carbon dioxide from the atmosphere and fixing it into biological material and soil compounds. Plants and animals effectively "burn" carbohydrates (and other products derived from them) in respiration. This yields energy for metabolism and renders the carbohydrate "fuel" back down to water and carbon dioxide. Decomposition by fungi and bacteria also breaks down the carbohydrates by using dead biological material as a working substance. Together, respiration and decomposition return the biologically-fixed carbon back to the atmosphere, completing the carbon cycle.

Over the past two decades, global vegetation has been affected by the increases in carbon dioxide by taking in more carbon dioxide and storing the fixed carbon in biomass or soil than it is releasing by respiration and decomposition. Why is this? Over the same period, air temperatures over the land have increased, resulting in a lengthened growing season in the northern and mid-latitudes. In fact, it seems that the northern spring now arrives approximately a week earlier than it did 20 years ago. Therefore, a gradual and slight warming seems to have favored photosynthesis over respiration-decomposition with far-reaching effects on the global carbon balance, as approximately one-quarter of our industrially-emitted carbon dioxide is now being fixed and stored by the vegetation. If this trend continues, the severity and onset of global warming might be delayed as increasing amounts of carbon dioxide are removed from the atmosphere and stored. However, some scientists warn that in the future, the biosphere could flip from being a net carbon sink (removing carbon dioxide) to a net carbon source (releasing carbon dioxide) over the next century.

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Changing Global Land Surface

Introduction

The Carbon Cycle

Greenhouse Warming

Plants, Snow & Ice

Terra & Landsat Observations