Science: Climate Modeling: Running Simulations Worksheet

Question 1

A simple climate model is run twice. In Run A, atmospheric carbon dioxide is set to 420 ppm. In Run B, carbon dioxide is set to 560 ppm, while all other settings remain the same. The model predicts a higher average global temperature in Run B. Identify the independent variable, the dependent variable, and one controlled variable in this simulation.

Accepted Answer

The independent variable is the atmospheric carbon dioxide concentration. The dependent variable is the predicted average global temperature. One controlled variable is any setting kept the same in both runs, such as solar input, land area, ocean coverage, or initial temperature.

Question 2

A climate simulation shows that global average temperature rises by 2.8 degrees Celsius after carbon dioxide is doubled from preindustrial levels. Explain what this result means and why it should not be treated as an exact prediction for a specific future year.

Accepted Answer

The result means that in this model, doubling carbon dioxide produces a 2.8 degrees Celsius increase in global average temperature after the climate system adjusts. It should not be treated as an exact prediction for a specific future year because real future temperatures depend on emissions, natural variability, feedbacks, land use, aerosols, and model assumptions.

Question 3

A student runs a climate model with three different surface albedo values: 0.20, 0.30, and 0.40. The predicted average temperatures are 18 degrees Celsius, 15 degrees Celsius, and 12 degrees Celsius. Describe the relationship shown by the simulation and explain the physical reason for it.

Accepted Answer

The simulation shows that higher albedo leads to lower average temperature. This happens because surfaces with higher albedo reflect more incoming sunlight back to space, so less solar energy is absorbed by Earth and the surface warms less.

Question 4

In a simulation, the model grid divides Earth into large boxes that are 100 kilometers wide. Explain one advantage and one limitation of using a grid in a climate model.

Accepted Answer

One advantage of using a grid is that it allows the model to calculate climate processes over the whole planet in an organized way. One limitation is that small-scale features, such as local storms, mountain effects, or city heat islands, may be simplified or missed because they are smaller than the grid boxes.

Question 5

A model run includes a positive ice-albedo feedback. The simulation begins with warming that melts some sea ice. Explain how this feedback can amplify warming.

Accepted Answer

When warming melts sea ice, darker ocean water is exposed. The darker surface has a lower albedo and absorbs more solar energy than ice. This extra absorption causes more warming, which can melt even more ice, so the original warming is amplified.

Question 6

A researcher runs an ensemble of 30 climate simulations using slightly different starting conditions. The runs produce a range of possible temperatures for the year 2100 rather than one value. Explain why scientists use ensembles and what the range of results tells them.

Accepted Answer

Scientists use ensembles because the climate system has natural variability and small differences in starting conditions can affect the path of a simulation. The range of results helps scientists estimate uncertainty and identify outcomes that are more or less likely under the same general scenario.

Question 7

A climate model produces the following projected global temperature changes for 2100 under three emissions scenarios: low emissions, 1.4 degrees Celsius; medium emissions, 2.6 degrees Celsius; high emissions, 4.3 degrees Celsius. Explain what this comparison shows about the role of human choices in climate projections.

Accepted Answer

The comparison shows that future warming depends strongly on emissions choices. Lower emissions lead to less projected warming, while higher emissions lead to much greater warming. This means climate projections are conditional results based on the scenario used, not fixed outcomes.

Question 8

A student changes both carbon dioxide concentration and solar input at the same time in a climate model. The model temperature increases, but the student concludes that carbon dioxide caused all of the warming. Explain why this conclusion is not well supported and how the experiment should be improved.

Accepted Answer

The conclusion is not well supported because two variables were changed at the same time, so the student cannot tell which variable caused the temperature increase or how much each contributed. The experiment should be improved by changing only one variable at a time while keeping the other variables constant, or by running separate controlled simulations.

Question 9

A model estimates Earth's energy balance. Incoming solar energy absorbed by Earth is 240 watts per square meter, and outgoing infrared radiation is 236 watts per square meter. Calculate the net energy imbalance and explain what it suggests about temperature change.

Accepted Answer

The net energy imbalance is 240 minus 236, which equals 4 watts per square meter. Because Earth is absorbing more energy than it emits, the model suggests that the climate system will continue warming until energy balance is restored.

Question 10

A climate simulation matches observed global temperature trends from 1980 to 2020 only when both greenhouse gases and aerosols are included. Explain what this suggests about model validation and the importance of including multiple climate forcings.

Accepted Answer

This suggests that the model is more realistic when it includes multiple climate forcings that affect temperature. Greenhouse gases tend to warm the planet, while some aerosols can reflect sunlight and cause cooling. Comparing model output with observations is part of validation, and a better match indicates that important processes are being represented more accurately.

Question 11

In one simulation, precipitation increases in high latitudes but decreases in some subtropical regions. Explain why a global climate model can predict different regional changes even when the global average temperature increases.

Accepted Answer

A global average temperature increase does not affect every region in the same way. Regional precipitation depends on atmospheric circulation, ocean temperatures, wind patterns, evaporation, topography, and storm tracks. A climate model can show different regional outcomes because it calculates how these processes interact across the planet.

Question 12

A policy group asks whether a climate model can prove exactly what the climate will be like in 2100. Write a short response explaining what climate models can and cannot do.

Accepted Answer

Climate models cannot prove exactly what the climate will be like in 2100 because future emissions, natural variability, and some feedbacks are uncertain. However, models can test scenarios, estimate likely trends, compare possible outcomes, and help scientists understand how changes in greenhouse gases, land use, aerosols, and other factors may affect the climate system.

Science: Climate Modeling: Running Simulations

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