Dansgaard-Oeschger cycles
Rapid climate oscillations -- a number of which occurred between 17,000 and 34,000 years ago, toward the end of the last ice age -- that induced major changes in Northern Hemisphere atmospheric circulation patterns, as well as large changes in temperature and precipitation.
Dark Ages Cold Period
The period between the 2nd and 8th centuries A.D. when global temperatures were colder than present.
Deciduous
Trees that usually possess broad leaves that are dropped in the cooler winter months prior to dormancy.
Decomposers
Organisms that feed on dead tissues of plants and animals and hasten the process of decomposition, whereby complex organic tissues are reduced to their more simple components.
Deforestation
The removal of trees from a previously pristine area, generally by logging to obtain lumber products.
Delta 13C
A measure of the relative proportions of two isotopes of carbon in some substance, such as the fossil remains of benthic or planktonic foraminifera, which is related to the temperature of the organism at the time it produced the substance.
Delta 18O
A measure of the relative proportions of two isotopes of oxygen in some substance, such as the fossil remains of benthic or planktonic foraminifera, which is related to the temperature of the organism at the time it produced the substance.
Dendrochronology
A means of reconstructing past climatic conditions by analyzing the annual growth rings of trees.
Desertification
The process by which lands become more desert-like, often driven by a number of complex interacting phenomena.
Desiccation-tolerant plants
Plants that posess physiological or anatomical adaptations that allow them to survive prolonged periods of drought.
Detritus
Organic debris derived from living organisms upon their death.
Diatom
A small, generally unicellular, alga that typically secretes a large quantity of silica about itself.
Dicotyledons
Plants that develop from seeds containing two cotyledons, which are specialized organs that contain food reserves to provide energy in germinating seeds and seedlings prior to food production via photosynthesis. Many "dicot" plants fix atmospheric carbon dioxide using C3 photosynthesis.
Dioecious
Plants that produce fertile male and female reproductive structures on different individuals, i.e., there are separate male and female plants.
Down regulation
A phenomenon exhibited by some plants following long-term exposure to elevated CO2 levels that is synonymous with acclimation. It is commonly characterized by decreases in leaf rubisco and nitrogen levels.