An Introduction to Climate Change - Grand Junction

An Introduction to Climate Change

Gerald C. Nelson

Professor Emeritus, University of Illinois, Urbana-Champaign

Presentation at Mesa County Library, August 4, 2014

What is climate change?

• Climate – average weather over an extended period, say 30 years

• Climate change – changes in those averages

• What weather variables? Some examples• Temperature – daily average, minimum, maximum

• Rainfall

• Heating degree days

• Etc.

Recent Climate Change in Grand Junction (1899 – 2013)

Summary of Climate Change in Grand Junction since 1899• It’s been getting hotter in the summer

• Maximum August temp increasing from 88°F to 90°F on average

• More days in August over 90°F (17°F in 1899 to 21°F in 2013)

• It’s been getting less cold at night in the winter• December minimums have been increasing

• Summer rains have been declining • August rainfall down (1.16 inches in 1899 to 0.8 inches in 2013)

• Note: All values are averages with lots of variation

Global Average Temperature Change, 1850-2012

Source: IPCC. http://www.climatechange2013.org/images/figures/WGI_AR5_FigSPM-1.jpg

Temperature Change Has Not Been Uniform

What causes warming/cooling?

• Start with sunlight falling on the earth

• Add greenhouse gasses to the atmosphere to get warming

• Add clouds that reflect sunlight to get cooling

• Add dust particles that can either reflect or absorb sunlight to get warming or cooling

What are the most important greenhouse gasses?

Gas Sources Global warming potential relative to carbon dioxide

Water vapor Evaporation from water bodies GWP of water vapor is not calculated because thereis no way to directly influence its concentration (see Scheevelpresentation)

Carbon dioxide Volcanoes, burning of organic material and fossil fuels

1

Methane Rice paddies, ruminant digestion, natural gas leaks

34 (over 100 years)

Nitrous oxide Fertilizer use, decomposition of manure, industrial processes, transportation

298 (over 100 years)

CO2 at Mauna Loa Observatory has been rising steadily …

http://www.esrl.noaa.gov/gmd/ccgg/trends/

The first time in at least 1 million years.

Other greenhouse gas emissions have also been rising

Page 11

From ‘agri-culture’

Scenarios of Annual CO2 Emissions to 2100 and modeled effects on temperature

Note: range of temperature increases by 2100

How well do the climate models do?