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Global warming and greenhouse gases

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Part of this lesson is original; much was adapted from: Climate Kids. Earth Science Communications Team at NASA’s Jet Propulsion Laboratory / California Institute of Technology, climatekids.nasa.gov/greenhouse-effect, and other parts came from Overview of Greenhouse Gases, EPA.gov

What is a greenhouse?

greenhouse 1

from climatekids.nasa.gov/greenhouse-effect

A building made of glass. We grow plants, flowers, crops, inside. They stay warm inside, even during winter.

Sunlight shines in and warms the plants and air inside.

Some of that light/heat bounces off surfaces, and goes out of the greenhouse.

But some is reflected back in by the glass, keeping it warm.

How is Earth like a greenhouse?

Greenhouse gases in the atmosphere do what a greenhouse does.

During the day, the Sun shines through the atmosphere, warming the air, land, and ocean.

At night, Earth cools, releasing heat back into the air. Much of that heat escapes out into space. But some is reflected back to the earth by the greenhouse gases in the atmosphere.

That’s what keeps Earth warm – 59 degrees Fahrenheit, on average.

(That’s an average. The equator would be hotter while the Arctic would be colder.)

greenhouse2

from climatekids.nasa.gov/greenhouse-effect

What causes global warming?

Having some greenhouse gases in the atmosphere in perfectly natural, and essential for life as we know it.  But human industrial activity has released vast amounts of additional greenhouse gases, at an accelerating rate, for the past three centuries. This has been increasing the greenhouse effect, leading to a marked warming of the earth – both our atmosphere and ocean.

This diagram offers a simplified view:

greenhouse 3

If the greenhouse effect is too strong, then Earth gets warmer and warmer.

This is what is happening now. Too much CO2 and other greenhouse gases in the air are making the greenhouse significantly effect stronger.

And this graph only shows rising surface temperatures.

Some of this heat also goes into the oceans. This next figure is based on data from a 2011 paper by Church et al.

Global 6th pic

Why not just plant more trees?

That would help, somewhat. Plants take in carbon dioxide and give off oxygen. But, instead of planting more forests, some people are cutting them down and burning them to make more farm land to feed the growing human population. And even planting more trees would not be enough to offset the vast amount of gases created by human industry.

greenhouse 5

A forest burns. (Photograph copyright Woods Hole Research Center).

Let’s put this all together into one graph

Greenhouse-effect US NPS

from US National Park Service

How does the ocean affect CO2 in the air

The ocean absorbs some excess CO2 – but unfortunately, that causes a chemical reaction which makes ocean water slightly more acidic.

Ocean creatures don’t like acidic water.

The bleached, unhealthy coral in this picture is just one example of what acidic water does.

greenhouse 6

Coral Bleaching – Great Barrier Reef

The Great Barrier Reef has experienced many coral bleaching events in recent years.

The coral bleaching was severe in 2002, when surveys showed almost 60% of the reefs experienced bleaching of some degree throughout the bleaching.

{ http://greatbarrierreefconsequences.weebly.com/coral-bleaching.html }

Coral Bleaching - Great Barrier Reef

Don’t clouds keep Earth cooler?

Water in the atmosphere also acts as a greenhouse gas.

The atmosphere contains a lot of water. It can be in the form of a gas—water vapor—or in the form of a liquid—clouds.

Clouds are water vapor that has cooled and condensed back into tiny droplets of liquid water.

The-Blue-Marble-from-Apollo-17
“The Blue Marble from Apollo 17, NASA”

Water in the clouds holds in some of the heat from Earth’s surface.

But the bright white tops of clouds also reflect some of the sunlight back to space.

So with clouds, some energy from the Sun never even reaches Earth’s surface.

How much the clouds affect the warming or cooling of Earth’s surface is one of those tricky questions that several NASA missions are aiming to answer.

greenhouse 7 cloudeffect2

Or do clouds make Earth warmer? As the ocean warms up, more water evaporates into the air. So does more water vapor then mean more warming? And does more warming mean more water vapor?

Greenhouse 8 cloud_greenhouse_effect-1

At night, clouds trap some of the heat from Earth’s surface. Thus, it does not escape back into space.

Or, since more water vapor means more clouds, will the clouds reflect enough sunlight back into space to make up for the warming?

greenhouse 9 cloud_greenhouse_effect-2

[ During the day, clouds reflect the Sun’s energy back to space, before it has a chance to heat Earth’s surface. ]

NASA is studying this question with satellites like Aqua and CloudSat, which study the Earth’s water cycle and clouds in 3-D.

greenhouse 10 CLOUDSAT_3dPrapiroon_eye

The top image is a hurricane, as seen by a satellite.

Below is a cross-section of the storm clouds, made with data from the CloudSat satellite.

It shows with different colors how much water is contained in the clouds at different heights.

 

Misconceptions: Ozone and global warming

Let’s differentiate between global warming and damage to the ozone layer.

Too much CFCs in the air leads to damage of the ozone layer.

Too many greenhouses gases in the air leads to global warming.

These are distinct phenomenon. 

Yes, CFCs are a greenhouse gas, so they contribute to both problems. However, most of the greenhouse effect comes from other greenhouse gases. CFCs aren’t affecting that issue very much.

What are the greenhouse gases?

Taken from EPA: Overview of Greenhouse Gases

  • Carbon dioxide (CO2): Carbon dioxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and wood products, and also as a result of certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.
  • Methane (CH4): Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the decay of organic waste in municipal solid waste landfills.
  • Nitrous oxide (N2O): Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of fossil fuels and solid waste.
  • Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes.Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).

Each gas’s effect on climate change depends on three main factors:

How much of these gases are in the atmosphere?

Concentration, or abundance, is the amount of a particular gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Greenhouse gas concentrations are measured in parts per million, parts per billion, and even parts per trillion. One part per million is equivalent to one drop of water diluted into about 13 gallons of liquid (roughly the fuel tank of a compact car). To learn more about the increasing concentrations of greenhouse gases in the atmosphere, visit the Causes of Climate Change and the Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases pages.

How long do they stay in the atmosphere?

Each of these gases can remain in the atmosphere for different amounts of time, ranging from a few years to thousands of years. All of these gases remain in the atmosphere long enough to become well mixed, meaning that the amount that is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.

How strongly do they impact the atmosphere?

Some gases are more effective than others at making the planet warmer and “thickening the Earth’s blanket.”

For each greenhouse gas, a Global Warming Potential (GWP) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per pound, than gases with a lower GWP, and thus contribute more to warming Earth.

Note: All emission estimates are from the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015.

Suggested viewing and reading

Dimming the SUN PBS
http://www.pbs.org/wgbh/nova/sun/

“Dimming the Sun” investigates the discovery that the sunlight reaching Earth has been growing dimmer, which may seem surprising given all the international concern over global warming. At first glance, less sunlight might hardly seem to matter when our planet is stewing in greenhouse gases. But the discovery of global dimming has led several scientists to revise their models of the climate and how fast it’s changing. According to one recent and highly controversial model, the worst-case warming scenario could be worse than anyone has predicted. “Dimming the Sun” unravels this baffling climate conundrum and the implications for Earth’s future.

To find out what global dimming means for the fate of the planet, NOVA reports on the findings of the world’s top climate detectives, including an American scientist who found a grim but crucial opportunity immediately following September 11, 2001, when the entire U.S. airline fleet was grounded for three days. This presented a unique opportunity to study the effects of airplane vapor trails on the atmosphere (see The Contrail Effect). Comparing changes in the daily temperature range showed that the absence of dimming from aircraft pollution alone made a marked difference to the temperature. This result hints at how much the effects of atmospheric pollution had been underestimated.

Working in Israel, Dr. Gerald Stanhill was one of the first to discover the surprising fact that less solar energy is reaching the Earth’s surface. While his measurements were met with skepticism, a review of worldwide data by Stanhill and a German researcher demonstrated that during the 1980s and early ’90s, sunlight reaching Earth’s surface had dropped just about everywhere. Halfway around the world, independent studies by Australian scientists confirmed this disturbing diagnosis. (For more, see Discoveries in Global Dimming.)

Scientists have long known that increasing air pollution—the smog that clouds urban skies—endangers our respiratory health. But they had underestimated the impact of pollution on the amount of sunlight reaching Earth. Some scientists now believe that global dimming may also disturb rainfall patterns such as the Asian monsoon. If they are right, global dimming may be one of many factors that contributed to severe droughts and famines in Africa during the 1980s.

The good news is that pollution controls have slowed and possibly even halted global dimming during the last decade. The bad news—and the ironic twist in NOVA’s story—is that without pollution, more sunlight is reaching Earth, revealing the full impact of global warming. Although all climate models have important uncertainties, the unsettling implication is that, with dimming fading away in many regions, global temperatures may rise even faster than most models have predicted.

Also see

What is Climate Change? U.S. NPS (National Park Service)

Climate Basics for Kids. C2ES. Center for Climate and Energy Solutions.
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XKCD Global Warming because what used to be nomal now feels too cold

Learning Standards

Massachusetts Curriculum FrameworksMassachusetts Curriculum Frameworks

Grades 6–8: Overview of Science and Engineering Practices

Examine and interpret data to describe the role human activities have played in the rise of global temperatures over time; construct, analyze, and/or interpret graphical displays of data and/or large data sets to identify linear and nonlinear relationships; distinguish between causal and correlational relationships in data; consider limitations of data analysis.

8.MS-ESS3-5. Examine and interpret data to describe the role that human activities have played in causing the rise in global temperatures over the past century.

High School. HS-ESS3-5. Analyze results from global climate models to describe how forecasts are made of the current rate of global or regional climate change and associated future impacts to Earth systems.
Clarification: Climate model outputs include both climate changes (such as precipitation and temperature) and associated impacts (such as on sea level, glacial ice volumes, and atmosphere and ocean composition).

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas

Disciplinary Core Ideas

LS2.C: Ecosystem Dynamics, Functioning, and Resilience
A complex set of interactions within an ecosystem can keep its numbers and types of organisms relatively constant over long periods of time under stable conditions. If a modest biological or physical disturbance to an ecosystem occurs, it may return to its more or less original status (i.e., the ecosystem is resilient), as opposed to becoming a very different ecosystem. Extreme fluctuations in conditions or the size of any population, however, can challenge the functioning of ecosystems in terms of resources and habitat availability. (HS-LS2-2),(HS-LS2-6)

Moreover, anthropogenic changes (induced by human activity) in the environment—including habitat destruction, pollution, introduction of invasive species, overexploitation, and climate change—can disrupt an ecosystem and threaten the survival of some species. (HS-LS2-7)

Cross Cutting Concepts

Cause and Effect:  Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects. (HS-LS2-8),(HS-LS4-6)

Scale, Proportion, and Quantity: The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs. (HS-LS2-1)

Using the concept of orders of magnitude allows one to understand how a model at one scale relates to a model at another scale. (HS-LS2-2)

Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable. (HS-LS2-6),(HS-LS2-7)

Next Generation Science Standards

HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

HS-ESS3-5. Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth’s systems.
[Clarification: Examples of evidence, for both data and climate model outputs, are for climate changes (such as precipitation and temperature) and their associated impacts (such as on sea level, glacial ice volumes, or atmosphere and ocean composition).]

[Assessment Boundary: Assessment is limited to one example of a climate change and its associated impacts.]

HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.

Earth and Human Activity Next Gen Science Standards

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