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Where Do Greenhouse Gas Emissions Come From?

What are greenhouse gases? What activities cause the most emissions? And why are scientists and policymakers concerned? This comic breaks it down.


What Is the Future of Solar Energy?

Though solar energy provides a sliver of the world's electricity now, it is on a trajectory to expand rapidly.

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What Is the Future of Wind Energy?

Humans have used windmills to capture the force of the wind as mechanical energy for more than 1,300 years. Today, wind energy is a small but fast-growing fraction of electricity production.

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­­­How Do We Remove CO2 and Where Does it Go?

Carbon dioxide is a greenhouse gas that traps heat and warms the planet. Learn about science and engineering solutions to mitigate CO2 by removing it from the atmosphere and using or storing it safely.

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What Role Do Batteries Play in Sustainability Solutions?

Innovations in energy storage are critical to the transition from fossil fuels to alternative sustainable energy sources.

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Can Our Electricity Grid Run on Alternative Energies?

Connecting renewable, or alternative, energy sources with the grid presents both opportunities and challenges.


How Do We Predict Climate Change?

To explore and predict how the climate will change, researchers create computer models of the real world.


What Causes Smog?

The main components of photochemical smog, the hazy air pollution that can blanket Los Angeles and other urban areas, are ground-level ozone and particulate matter.


How Can We Reduce Plastic Pollution?

Plastic is incredibly useful in modern life, but the production and disposal of plastic generates greenhouse gases and hazardous waste.

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How Can We Ensure Sustainable Access to Water?

The global supply of fresh water is dwindling. Natural and human causes can impact water availability, and scientific, technological, and policy solutions can protect access to water for all.

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What Is the Evidence for Human-Caused Climate Change?

The warming we've seen over the past few decades is too rapid to be linked to changes in Earth's orbit and too large to be caused by solar activity.

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What Are the Effects of Climate Change?

Global climate change has already had observable effects on the environment.

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Ask a Caltech Expert

Caltech researchers answer questions about sustainability science and solutions.

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Terms to Know

Sources of energy that are not readily depleted when used and generally do not pollute the environment. Examples of renewable energies include solar, wind, hydroelectric, and geothermal.

An underground layer of rock and sediment that holds and transmits groundwater. Humans can extract this water for drinking, as it is cleaned by natural processes. Groundwater can be contaminated by human and natural activities.

Materials are considered biodegradable if they can be broken down by natural processes, ideally without leaving pollutants behind.

The regions of the earth occupied by living organisms. This can be anywhere on the planet, including on the surface, underground, and in the ocean.

The most abundant greenhouse gas. While carbon dioxide is emitted naturally, for example through volcanic eruptions or the decomposition of plants and microbes, human activities, such as burning fossil fuels, are responsible for an unprecedented increase in the amount of carbon dioxide in the atmosphere.

A measurement of the amount of greenhouse gases emitted by a process or entity, and therefore, its impact on Earth's climate.

A reservoir for carbon-containing material. Examples include forests, which absorb large amounts of atmospheric carbon dioxide for photosynthesis, and oceans, which absorb atmospheric carbon dioxide through natural processes.

The average weather in a region over a long period of time (generally, 30 years or more). The average temperature in a given season or the amount of precipitation in a year are properties of the climate.

The change over time in Earth's processes and cycles, including shifts in temperature, sea level, and the intensity of storms. While Earth's climate has changed throughout history due to its position in space relative to the sun and natural occurrences like volcanic eruptions, the planet's current warming trend is extremely likely to be the result of human activity since the mid-19th century.

A computer simulation that combines scientific theory and data collected from the physical, chemical, and biological process on Earth and in Earth's atmosphere to predict climate in the past, present, and future.

Non-renewable energy resources, such as oil, coal, and natural gas, that were formed by decomposed prehistoric plants and animals in the earth's crust. Over the past 20 years, nearly three-fourths of human-caused emissions came from the burning of fossil fuels.

Interventions that modify the atmosphere and alter climate and weather. Geoengineering is being explored as a way to combat global warming. For example, solar geoengineering proposes reflecting sunlight away from the earth.

A gas that traps thermal radiation from the earth, heating the planet (a process known as the greenhouse effect). Greenhouse gases include carbon dioxide, methane, and nitrous oxide. While greenhouse gases are naturally occurring, human activities, including burning fossil fuels, produce them in large and harmful quantities.

A network of systems that generate, transmit, and distribute electricity across long and short distances. Grids can distribute energy from renewable and nonrenewable sources.

A greenhouse gas that is more potent but less abundant and shorter lived in the atmosphere than carbon dioxide. Methane is emitted naturally (e.g. from microbial activity in wetlands) and by humans (e.g. from landfills, coal mines, agriculture, and oil and natural gas operations).

Meeting the needs of the present without compromising the needs of future generations. (From "Our Common Future," also known as the Brundtland Commission Report of 1987).

Dive Deeper

A collage of images including a container ship, a plastic bottle on soil, a cow near wheat, and a picture of the planet Earth
A Quantitative Snapshot of the Human Impact on the Planet
An image of a chalkboard and wall inside the Resnick Sustainability Institute building
Ten Years of Research Through the Resnick Sustainability Institute
A glacier reflected in a lake
International Alliance of Universities Urges G20 Leaders to Create a Zero-Emission World