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It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years.cite

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In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming. cite

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Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the Industrial Revolution. Changes that have historically taken thousands of years are now happening over the course of decades.

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Glaciers are melting, sea levels are rising, cloud forests are dying, and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years.

Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts. All of those changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere, changing the rhythms of climate that all living things have come to rely on.

What will we do-what can we do-to slow this human-caused warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the fate of the Earth as we know it-coasts, forests, farms, and snow-capped mountains-hangs in the balance.

Understanding the greenhouse effect

The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.

Sunlight shines onto the Earth's surface, where the energy is absorbed and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.

Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.

Aren't temperature changes natural?

Human activity isn't the only factor that affects Earth's climate. Volcanic eruptions and variations in solar radiation from sunspots, solar wind, and the Earth's position relative to the sun also play a role. So do large-scale weather patterns such as El Niño.

For thousands of years now, emissions of greenhouse gases to the atmosphere have been balanced out by greenhouse gases that are naturally absorbed. As a result, greenhouse gas concentrations and temperatures have been fairly stable, which has allowed human civilization to flourish within a consistent climate.

Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the Industrial Revolution. Changes that have historically taken thousands of years are now happening over the course of decades.

The rapid rise in greenhouse gases is a problem because it's changing the climate faster than some living things can adapt to. Also, a new and more unpredictable climate poses unique challenges to all life.

Historically, Earth's climate has regularly shifted between temperatures like those we see today and temperatures cold enough to cover much of North America and Europe with ice. The difference between average global temperatures today and during those ice ages is only about 9 degrees Fahrenheit (5 degrees Celsius), and the swings have tended to happen slowly, over hundreds of thousands of years.

As the mercury rises, the climate can change in unexpected ways. In addition to sea levels rising, weather can become more extreme. This means more intense major storms, more rain followed by longer and drier droughts-a challenge for growing crops-changes in the ranges in which plants and animals can live, and loss of water supplies that have historically come from glaciers.

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Glaciers are melting, sea levels are rising, cloud forests are dying, and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives.

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MITIGATION
RENEWABLE ENERGY

CARBON DIOXIDE (CO2)

GREENHOUSE GAS

EMISSIONS

CLIMATE CHANGE

GLOBAL WARMING

FOSSIL FUELS

SEA-LEVEL RISE

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We're at a historic moment with the UNFCCC COP 21, United Nations Framework Convention on Climate Change, 21st Conference of the Parties, in Paris set to begin next month. With world leaders from 195 countries negotiating to reach a global agreement to reduce carbon emissions, expansive news and media coverage is guaranteed. What's also guaranteed in this coverage is a host of scientific jargon and acronyms that can be overwhelming to follow, let alone understand.

So this week we're breaking down climate science to its most basic key terms and phrases to help you better grasp what's going on in the world with climate change, both at the UN climate talks and beyond.

We've got a lot of ground to cover, so let's jump right in. Below is our list of the top terms you need to know to understand the basic science and political sphere of climate change.

1. Carbon dioxide (CO2)

The chemical compound carbon dioxide (also known by its shorthand CO2) is the primary greenhouse gas and driver of climate change. It's an integral part of life cycles on earth, produced through animal respiration (including human respiration) and absorbed by plants to fuel their growth, to name just two ways. Human activities are drastically altering the carbon cycle in many ways. Two of the most impactful are: one, by burning fossil fuels and adding more carbon dioxide into the atmosphere; and two, by affecting the ability of natural sinks (like forests) to remove carbon dioxide from the atmosphere.

2. Greenhouse Gas

A greenhouse gas is a chemical compound found in the Earth's atmosphere, such as carbon dioxide, methane, water vapor, and other human-made gases. These gases allow much of the solar radiation to enter the atmosphere, where the energy strikes the Earth and warms the surface. Some of this energy is reflected back towards space as infrared radiation. A portion of this outgoing radiation bounces off the greenhouse gases, trapping the radiation in the atmosphere in the form of heat. The more greenhouse gas molecules there are in the atmosphere, the more heat is trapped, and the warmer it will become.

3. Emissions

In the climate change space, emissions refer to greenhouse gases released into the air that are produced by numerous activities, including burning fossil fuels, industrial agriculture, and melting permafrost, to name a few. These gases cause heat to be trapped in the atmosphere, slowly increasing the Earth's temperature over time.

It's all about timing when it comes to differentiating weather and climate. Weather refers to atmospheric conditions in the short term, including changes in temperature, humidity, precipitation, cloudiness, brightness, wind, and visibility.

While the weather is always changing, especially over the short term, climate is the average of weather patterns over a longer period of time (usually 30 or more years). So the next time you hear someone question climate change by saying, "You know it's freezing outside, right?", you can gladly explain the difference between weather and climate.

5. Global warming vs climate change

Many people use these two terms interchangeably, but we think it's important to acknowledge their differences. Global warming is an increase in the Earth's average surface temperature from human-made greenhouse gas emissions.

On the other hand, climate change refers to the long-term changes in the Earth's climate, or a region on Earth, and includes more than just the average surface temperature. For example, variations in the amount of snow, sea levels, and sea ice can all be consequences of climate change.

6. Fossil Fuels

Fossil fuels are sources of non-renewable energy, formed from the remains of living organisms that were buried millions of years ago. Burning fossil fuels like coal and oil to produce energy is where the majority of greenhouse gases originate. As the world has developed and demand for energy has grown, we've burned more fossil fuels, causing more greenhouse gases to be trapped in the atmosphere and air temperatures to rise.

7. Sea-Level Rise

Sea-level rise as it relates to climate change is caused by two major factors. First, more water is released into the ocean as glaciers and land ice melts. Second, the ocean expands as ocean temperatures increase. Both of these consequences of climate change are accelerating sea-level rise around the world, putting millions of people who live in coastal communities at risk.

8. Global average temperature

Global average temperature is a long-term look at the Earth's temperature, usually over the course of 30 years, on land and sea. Because weather patterns vary, causing temperatures to be higher or lower than average from time to time due to factors like ocean processes, cloud variability, volcanic activity, and other natural cycles, scientists take a longer-term view in order to consider all of the year-to-year changes.
RELATED: Ten Clear Indicators Our Climate Is Changing
9. Renewable energy

Renewable energy is energy that comes from naturally replenished resources, such as sunlight, wind, waves, and geothermal heat. By the end of 2014, renewables were estimated to make up almost 28% of the world's power generating capacity, enough to supply almost 23% of global electricity. Because renewables don't produce the greenhouse gases driving climate change, shifting away from fossil fuels to renewables to power our lives will put us on the path to a safe, sustainable planet for future generations.

10. COP and UNFCCC

These two abbreviations are best described together as they work hand-in-hand. The United Nations Framework Convention on Climate Change (UNFCCC) is an environmental treaty that nations joined in 1992, with the goal of stabilizing greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous human interference with the climate system.

Meanwhile, the Conference of the Parties (COP) to the UNFCCC is a yearly international climate conference where nations assess progress and determine next steps for action through the UNFCCC treaty. This year marks the 21st Conference of the Parties (COP 21), which will be held in Paris beginning November 30. Here, a historic global agreement to reduce greenhouse gas emissions is on the table and, if passed, will mark a landmark achievement in the fight against climate change.

11. INDC

INDC stands for "Intended Nationally Determined Contribution." In preparation for the UN climate talks later this year, countries have outlined what actions they intend to take beginning in 2020 under a proposed global climate agreement. These plans are known as INDCs, which will play a big part in moving us forward on the path toward a low-carbon, clean energy future.

12. IPCC

IPCC is the acronym for the Intergovernmental Panel on Climate Change. First set up in 1988 under two UN organizations, the IPCC surveys the research on climate change happening all around the world and reports to the public about the current state of our scientific knowledge.

13. PPM

PPM stands for "parts per million," which is a way of expressing the concentration of one component in the larger sample. Climate scientists and activists use the term to describe the concentration of pollutants, like carbon dioxide or methane, in the atmosphere. Many scientists agree that carbon dioxide levels should be at 350 PPM to be considered safe; we're at about 400 PPM right now and this number is growing by approximately 2 PPM each year.

14. Pre-Industrial Levels of Carbon Dioxide

Pre-industrial levels of carbon dioxide refers to carbon dioxide concentration in the atmosphere prior to the start of the Industrial Revolution. Scientists estimate these pre-industrial levels were about 280 PPM, well below where we are today.

Methane is a chemical compound that's the main component of natural gas, a common fossil fuel source. Just like carbon dioxide, methane is a greenhouse gas that traps heat in the atmosphere. Methane accounts for about 10 percent of all US greenhouse gas emissions (using 2013 figures), second only to carbon dioxide.

Many people don't understand the negative effects of methane as an alternative to other fossil fuels. While methane doesn't stay in the atmosphere as long as carbon dioxide, it absorbs 84 times more heat, making it very harmful to the climate.

Mitigation refers to an action that will reduce or prevent greenhouse gas emissions, such as planting trees in order to absorb more CO2. It can also include developing and deploying new technologies, using renewable energies like wind and solar, or making older equipment more energy efficient.
Photo: © 2012 martinak15/Flickr cc by 2.0
Stay tuned for more climate science coming up in future blog posts. In the meantime, sign up for our email activist list and we'll keep you up to date on what's happening and how you can get involved in the movement for climate solutions.

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Key Terms You Need to Understand Climate Change

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We're bringing back the basics in this post with our top climate change terms.

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https://www.nationalgeographic.com/environment/global-warming/global-warming-overview/     https://www.nationalgeographic.com/environment/global-warming/global-warming-overview/

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Global warming isn't just affecting weather. It's affecting animals, making them adapt to warmer climates. This could break down the food chain if one animal is gone from global warming and then other animals will either die off or populate too much.

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Carbon dioxide is the main contributor to climate change, especially through the burning of fossil fuels. https://davidsuzuki.org/what-you-can-do/greenhouse-gases/

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The amount of greenhouse gases deteriorate the ozone layer that protects us from harmful rays of sunlight.

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Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century and is accelerating slightly every year. https://climate.nasa.gov/evidence/

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The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of more than 0.4 degrees Fahrenheit since 1969. https://climate.nasa.gov/evidence/

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Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year — from January through September, with the exception of June — were the warmest on record for those respective months. https://climate.nasa.gov/evidence/

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The planet's average surface temperature has risen about 1.62 degrees Fahrenheit (0.9 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. https://climate.nasa.gov/evidence/

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Global Warming has increased more in seventy years than in thousands. https://climate.nasa.gov/evidence/

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Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 11,700 years ago marking the beginning of the modern climate era. https://climate.nasa.gov/evidence/