Feedbacks
This type of feedback counteracts an initial change, like a thermostat stabilizing temperature.
What is negative feedback?
This prehistoric period 21,000 years ago featured large ice sheets over North America and Europe.
What is the Last Glacial Maximum?
This percentage of global-warming heat ends up in the ocean.
What is about 90%?
This region of the planet is warming nearly four times faster than the global average.
What is the Arctic?
This term refers to the difference between incoming solar radiation and outgoing energy and is a key driver in climate model projections.
What is radiative forcing?
This greenhouse gas supplies a major positive feedback because warmer air can hold more of it.
What is water vapor?
Sediment cores track past ice volume using this oxygen-isotope ratio.
What is δ18O?
This process—responsible for ~40% of sea level rise—occurs because warm water takes up more space.
What is thermal expansion?
Permafrost can contain up to this many gigatons of carbon—far more than humans have emitted.
What is about 1700 GtC?
These two major types of atmospheric motion—horizontal and vertical—are calculated in climate models to simulate wind and convection.
What are horizontal air movement (wind) and vertical air movement (convection)?
This feedback occurs because snow and ice reflect more sunlight than darker surfaces.
What is the surface albedo feedback?
This set of orbital cycles explains long-term variations in Earth’s insolation.
What are the Milankovitch cycles (eccentricity, obliquity, precession)?
About 45% of sea-level rise comes from the melting of these two major types of ice sources.
What are glaciers and ice sheets?
Thawing permafrost releases carbon that is often thousands of years old; one experiment found carbon this old.
What is 30,000 years old?
Increasing this property of a climate model allows features like mountains, coastlines, and vegetation zones to be represented more accurately.
What is spatial resolution?
These low-altitude clouds cool the surface because they reflect sunlight but trap little infrared heat.
What are low cumulus clouds?
This “snowball” climate state 720–660 million years ago saw ice reach the tropics.
What is the Sturtian Snowball Earth?
This satellite mission measures changes in the mass of major ice sheets like Greenland.
What is GRACE (Gravity Recovery and Climate Experiment)?
This process increases with higher temperature as soil microbes respire faster, emitting more CO₂.
What is soil respiration?
Climate models only reproduce the observed warming trend of the 20th century when these human-caused factors are included.
What are anthropogenic forcings, especially greenhouse gases?
Shrinking low-cloud cover with warming is considered this type of feedback.
What is positive feedback (because less solar reflection increases warming)?
This evidence—still occurring today—shows Earth’s crust rising where ice sheets once sat.
What is post-glacial rebound (isostatic rebound)?
This feedback occurs when declining Arctic sea ice causes more solar absorption by open water.
What is the surface albedo positive feedback?
This land-based process both reduces carbon uptake and releases previously stored carbon, causing some Amazon regions to shift from carbon sinks to carbon sources.
What is deforestation?
These scenarios combine socioeconomic pathways with assumed radiative forcing values to project future climate—examples include 2.6, 4.5, and 8.5.
What are the Representative Concentration Pathways (RCPs)?