Climate Change and Greenhouse Gases: An Introduction

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In order to understand climate change we have to talk about “greenhouse gases,” what they are, where they come from, and how they contribute to what is known as “global warming.”

Definition of Greenhouse Gas: a gas that absorbs infrared radiation produced by solar warming of the Earth’s surface.

Definition of Global Warming: a gradual increase in the overall temperature of the earth's atmosphere generally attributed to the greenhouse effect caused by increased levels of carbon dioxide, CFCs, and other pollutants

First, what is Earth’s atmosphere composed of? More than 99.95% of it is made up of nitrogen and oxygen, water vapor, and argon. The largest part of the remaining 0.05% is carbon dioxide, which makes up about 0.039% of the atmosphere. Carbon dioxide absorbs infrared photons and is therefore a greenhouse gas.

Scientists express the concentration of trace gases like carbon dioxide in “parts per million,” indicating how many molecules out of every million are the gas in question. In this case, carbon dioxide corresponds to 390 parts per million (ppm), meaning that there are 390 molecules of carbon dioxide in every million molecules of air.

The next most important greenhouse gas in our atmosphere is nitrous oxide, which is present in today’s atmosphere at concentrations of about 0.3 ppm. You might know this molecule as “laughing gas.” It’s emitted into the atmosphere from nitrogen-based fertilizer and industrial processes as well as several natural sources.

Halocarbons (chlorofluorocarbons and hydrochlorofluorocarbons), which are synthetic industrial chemicals used as refrigerants, are present in today’s atmosphere at a concentration of a few parts per billion.

The final greenhouse gas in our atmosphere is ozone, and its abundance is about 10 ppb (parts per billion) in unpolluted air near the surface; but can reach 10 ppm (parts per million) in the stratosphere. Ozone is necessary for life on Earth because it absorbs high-energy ultraviolet photons emitted by the Sun before they reach the Earth’s surface. It’s also one of the primary components of smog, and breathing it can lead to health problems. You want ozone between you and the Sun, but you don’t want to breath it.

Greenhouse gases are not equal in their ability to warm the planet. The most powerful greenhouse gases on a per molecule bases are the halocarbons. It takes several thousand carbon dioxide molecules to equal the warming from one halocarbon molecule.

The main source of the increase in carbon dioxide has been through the burning of fossil fuels for energy, which are primarily carbon. Evidence shows that atmospheric carbon dioxide began rapidly increasing right at the beginning of the industrial revolution, when the widespread burning of fossil fuels began. Prior to 250 years ago atmospheric carbon dioxide remained in a narrow range of 260-280 ppm, but has increased by 100 ppm in the last 250 years; with half of that over the past 30 years.

Fundamental physics lead us to conclude that humans are now changing the climate, and that the continuing addition of greenhouse gases to the atmosphere will bring potentially significant changes to our climate over the next century and beyond. If the annual average warming of 5 degrees Celsius or more by the end of this century, experts consider the impact will be catastrophic.

It’s going to be very expensive to reduce emissions, to rebuild our energy infrastructure to switch from fossil fuels to renewables and other climate-safe energy sources; but fossil fuels will be exhausted in the next century or so anyway, so switching away from fossil fuels is inevitable. If we continue emitting carbon dioxide there is no practical way to remove it from the atmosphere.

The possible scenarios of doing nothing include catastrophic outcomes like abrupt climate changes that result in mass starvation or even human extinction. Reductions in emissions require collective, coordinated action by society as a whole. The single most important thing you can do is vote for politicians who support action on climate. Even better would be to become politically active. Write letters to your representatives, participate in rallies, talk to your friends and neighbors.

The above is from Introduction to Modern Climate Change, by Andrew E. Dessler (PhD Harvard), professor of atmospheric sciences at Texas A&M University. Prof. Dessler has also written The Science and Politics of Global Climate Change: A Guide to the Debate.

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CLIMATE CHANGE BASICS: From the Environmental Protection Agency

http://www.epa.gov/climatechange/basics/

Our Earth is Warming

Earth's average temperature has risen by 1.4°F over the past century, and is projected to rise another 2 to 11.5°F over the next hundred years. Small changes in the average temperature of the planet can translate to large and potentially dangerous shifts in climate and weather.

The Evidence is Clear

Rising global temperatures have been accompanied by changes in weather and climate. Many places have seen changes in rainfall, resulting in more floods, droughts, or intense rain, as well as more frequent and severe heat waves. The planet's oceans and glaciers have also experienced some big changes - oceans are warming and becoming more acidic, ice caps are melting, and sea levels are rising. As these and other changes become more pronounced in the coming decades, they will likely present challenges to our society and our environment.

Humans are Largely Responsible for Recent Climate Change

Over the past century, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere. The majority of greenhouse gases come from burning fossil fuels to produce energy, although deforestation, industrial processes, and some agricultural practices also emit gases into the atmosphere.

Greenhouse gases act like a blanket around Earth, trapping energy in the atmosphere and causing it to warm. This phenomenon is called the greenhouse effect and is natural and necessary to support life on Earth. However, the buildup of greenhouse gases can change Earth's climate and result in dangerous effects to human health and welfare and to ecosystems.

The choices we make today will affect the amount of greenhouse gases we put in the atmosphere in the near future and for years to come.

Climate Change Indicators in the United Stages

Over the last several decades, evidence of people's influences on climate change has become increasingly clear and compelling. Warming of the climate system is well-documented--evident from increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising sea levels.

EPA is working with many other organizations to better understand the causes and effects of climate change. With help from these partners, EPA produced a report, Climate Change Indicators in the United States, that presents 24 indicators that show trends related to the causes and effects of climate change. Most of the indicators focus on the United States, but some include global trends to provide context or a basis for comparison. These indicators represent a selected set of key climate change measurements, and are not an exhaustive group of all climate change indicators.

EPA's indicators are based on peer-reviewed data from various government agencies, academic institutions, and other organizations. EPA selected these indicators based on the quality of the data and other criteria. Each indicator features easy-to-understand graphs or maps, along with a description of key points, data sources, and any factors that might contribute to the overall confidence of the indicator and the underlying trends. Ultimately, these indicators will help EPA and its constituents evaluate the progress of their efforts to respond to climate change and effectively communicate observed climate change impacts.

Indicators are important because they help scientists, analysts, decision-makers, educators, and others assess trends in environmental quality, factors that influence the environment, and effects on ecosystems and evaluating existing and future programs. They also provide sound science to inform decision-making and facilitate meaningful communication.

Scientific Consensus on Climate Change

The major scientific agencies of the United States — including the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) — agree that climate change is occurring and that humans are contributing to it. In 2010, the National Research Council concluded that "Climate change is occurring, is very likely caused by human activities, and poses significant risks for a broad range of human and natural systems". Many independent scientific organizations have released similar statements, both in the United States and abroad. This doesn't necessarily mean that every scientist sees eye to eye on each component of the climate change problem, but broad agreement exists that climate change is happening and is primarily caused by excess greenhouse gases from human activities.

Scientists are still researching a number of important questions, including exactly how much Earth will warm, how quickly it will warm, and what the consequences of the warming will be in specific regions of the world. Scientists continue to research these questions so society can be better informed about how to plan for a changing climate. However, enough certainty exists about basic causes and effects of climate change to justify taking actions that reduce future risks.

http://nas-sites.org/americasclimate...-final-report/

How A Change of One or Two Degrees in Global Average Temperatures Can Have an Impact on Our Lives

Changing the average global temperature by even a degree or two can lead to serious consequences around the globe. For about every 2°F of warming, we can expect to see:

1. 5—15% reductions in the yields of crops as currently grown.

2. 3—10% increases in the amount of rain falling during the heaviest precipitation events, which can increase flooding risks.

3. 5—10% decreases in stream flow in some river basins, including the Arkansas and the Rio Grande.

4. 200%—400% increases in the area burned by wildfire in parts of the western United States.

Global average temperatures have increased more than 1.4 degrees Fahrenheit over the last 100 years. Many of the extreme precipitation and heat events that we have seen in recent years are consistent with what we would expect given this amount of warming. Scientists project that Earth's average temperatures will rise between 2 and 12 degrees Fahrenheit by 2100.

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Now, for an educational film. From The National Academies, “What is Climate? Climate Change, Lines of Evidence: Chapter 1