Climate science part 3 - climate models and predicted climate change

Climate Science:Part 3. Climate Models and Predicted Climate Change

Pam Knox, Agricultural Climatologist, University of Georgia

Topics you will learn about

• Review: Causes of changes in climate

• Carbon dioxide and other gases

• Methods for predicting climate

• Predicted changes in climate

Climate and Energy Balance

Climate of the Last 100 Years

Changes in Atmospheric Composition

Changes in Atmospheric Composition

Review of Climate Trends

What kinds of trends are there?

• Linear• Exponential• Changing variability• Change in slope• Step function

Atmospheric Window

The “atmospheric window” refers to the wavelengths at which light can enter the Earth’s atmosphere as solar radiation (rainbow at left) or leave it as terrestrial radiation (red bar).

As the amount of carbon dioxide, methane, water vapor and other greenhouse gases increases, the part of the window that lets light energy back to space gets pinched and energy stays in the climate system, which causes the climate to get warmer.

How to Predict Climate

You can predict climate by predicting trends, but that depends on things continuing the same way they have in the past. Not always a good assumption!

Instead, climatologists use climate models to simulate the future climate based on physics and predictions of future CO2 and other emissions.

Climate Models

Increasing Model Complexity

Global Climate Models

Global Climate Models

Problems with Models

• Coarse resolution leaves out mountains, Great Lakes, alters local conditions like coastlines

• Simplification processes make rainfall less believable since most of it happens in sub-gridscale processes like thunderstorms

• They are not very good at predicting current climate, making them less believable

• No El Niño, hurricanes

Weather vs. Climate Models

Weather models are designed to predict detailed hourly weather information for up to 7 days across a continent.

Emphasis: short term, individual storm evolution

Climate models are designed to predict multi-year climate conditions across the entire globe.

Emphasis: long-term, seasonal to multi-year average climate conditions

Models can separate out C02 effects

Models can be used to separate out the effects of individual factors to see what effect each factor has on the temperature trend.

Scenario ModelingModelers use scenarios of various projections of changing CO2, changing energy efficiency, etc. to produce a series of graphs giving a range of expected outcomes.

Observations don’t always agree with predictions. So which is right?

Sea Ice

For sea ice, the observed decline in sea ice cover in the Arctic is faster than any of the models predicted.

Predictions of Future Temperature

• Temperatures will increase, day and night• Amount of warming is not certain (5-10 F in

next 100 years)• Longer growing season• Increased evaporationhttp://www.globalchange.gov/nca3-downloads-materials (new site with similar material has replaced original site)

Predictions for Future Precipitation

• Predictions of future rainfall are not well modeled• Trends indicate increased rainfall intensity (more

thunderstorms) with longer dry spells in between• Precipitation changes by season cannot be

predicted• Effects on El Niño and hurricane frequency not

known

Secondary Impacts-Sea Level

Secondary Impacts-Other

Things that are Harder to Predict

Summary of Part 3

In this section we have covered:

• Changes in atmospheric composition• Climate models• Trends in climate

For a full list of references cited in this presentation, please visit:

www.animalagclimatechange.org

This project was supported by Agricultural and Food Research Initiative Competitive Grant No. 2011-67003-

30206 from the USDA National Institute of Food and Agriculture.