Climate Variability/ENSO
What is climate internal variability?
Natural changes in the climate system around its long-term average, occurring over months, years, or decades.
What is a climate model?
A numerical representation of Earth’s climate system based on physical, chemical, and biological processes.
What is the main role of the IPCC?
To assess and synthesize published climate research for governments and the public.
Several simulations use the same model and emissions scenario but begin with slightly different initial conditions. What source of uncertainty do they represent?
Internal variability.
Which ENSO phase is associated with weaker trade winds and unusually warm surface water in the central and eastern tropical Pacific?
El Niño.
Why do climate models divide Earth into three-dimensional grid cells?
To solve equations for energy, mass, momentum, water, and other properties across space and through time.
What is CMIP, and why is it useful?
The Coupled Model Intercomparison Project coordinates experiments across many climate models, allowing scientists to compare their results.
Two climate models use the same emissions scenario but project different amounts of warming. What source of uncertainty does this represent?
Model uncertainty.
During El Niño, why does rainfall generally shift eastward across the tropical Pacific?
Weaker trade winds allow warm water and rising air to shift eastward. The main region of convection and rainfall moves with the warm water.
What is a parameterization, and why do climate models need one?
A simplified representation of a process that occurs at scales too small or complex for the model to resolve directly, such as clouds.
Why is a climate projection described as an “if–then” statement rather than an exact prediction?
It estimates what is likely to happen if greenhouse-gas emissions and other forcings follow a particular pathway.
Projections following a low-emissions and a high-emissions scenario separate strongly late in the century. What source of uncertainty causes this separation?
Scenario uncertainty.
Explain how the Bjerknes feedback strengthens an El Niño event.
Weaker trade winds reduce the westward movement of warm surface water and weaken eastern-Pacific upwelling. The eastern Pacific warms, reducing the east–west temperature difference and weakening the trade winds further.
Name the three major sources of uncertainty in future climate projections and explain when each is most important.
Internal variability is especially important over shorter periods; model uncertainty results from differences among models; scenario uncertainty becomes increasingly important later in the century as emissions pathways separate.
How are the IPCC, CMIP, and SSPs connected?
SSPs describe possible future societal and emissions pathways. CMIP coordinates model simulations under those pathways. The IPCC assesses and synthesizes the resulting research.
An unusually warm El Niño year occurs during a long-term warming trend. Why can that single year not tell us how much climate change has occurred?
Why can an El Niño year be much warmer than expected from the gradual, long-term warming trend?
El Niño is a temporary expression of internal variability. Climate change is identified from long-term changes in averages, distributions, and extremes—not from one unusual year.
El Niño adds short-term internal climate variability on top of the long-term warming trend.