The Basics

C2ES is a source of reliable information about the causes and potential consequences of climate change. The basics page provides an overview of fundamental facts and data and answers to frequently asked questions.
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Tipping points and climate change: Revisiting The Day After Tomorrow

It has been 10 years since the movie The Day After Tomorrow offered a highly embellished vision of a climate “tipping point” in which polar ice sheets melt, shut down the Gulf Stream, and plunge Europe and much of the U.S. into a deep freeze.

While most of The Day After Tomorrow is safely in the realm of science fiction, there is real science to back up concerns that tipping points in the climate system could cause potentially irreversible, and in some cases drastic, changes in our climate.

Figure 1: Potential tipping elements in the Earth’s climate system overlaid with population density. Question marks indicate systems whose status as tipping elements is particularly uncertain. Source: National Climate Assessment 2014.


Kids Corner

Welcome Kids!

Weather vs. Climate

Weather refers to the state of the atmosphere over several minutes up to several days. It includes lots of things that should be familiar - temperature, humidity, rain, snow, wind speeds, or wind direction. Climate refers to the long-term average (and other statistics) of weather measured over long periods of time (at least several decades). 

Here’s a simple way to think about it: Climate is what you expect, but weather is what you get.  Say you were going to visit Southern California for a few days in April. You would expect it to be sunny and pleasant, because that’s what the climate of Southern California is usually like in April.  It might turn out to be sunny during your trip, or it could rain, be cloudy, chilly or hot.  All of those are examples of the weather during those few days.

The C2ES Kids Corner is designed to help you understand how and why our climate is changing, how climate change affects us, and what people can do to slow climate change and prepare for it.

We’ll explain the science behind climate change, the impacts of climate change, and how you can help.

The Science

The Greenhouse Effect and Climate Change

The picture below shows the greenhouse effect. It is a natural process that warms the planet. Light from the sun passes through the atmosphere and is absorbed by the Earth's surface, warming it. Greenhouse gases, like carbon dioxide, act like a blanket, trapping heat near the surface and raising the temperature.

Human activities are increasing the amount of greenhouse gases in the atmosphere.  This traps more heat. In other words, as we add more greenhouse gases, we thicken the blanket that traps heat near the surface.  This process is referred to as the human-induced greenhouse effect.

Greenhouse gases stay in the atmosphere for a long time. Although plants and the ocean absorb carbon dioxide, they can’t keep up with all the extra carbon dioxide that people have been putting into the atmosphere. So the amount of carbon dioxide in the atmosphere has been increasing over time.


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Source: National Park Service

Where do greenhouse gases come from?

Up until about 150 years ago, human activity did not produce many greenhouse gases. That changed as many important inventions and industrial innovations, like the widespread use of electricity and cars, transformed the way we live.

These inventions and innovations demand energy. Burning fossil fuels — coal, oil, and natural gas — became an important source of that energy. Burning fossil fuels releases carbon dioxide and other greenhouse gases into the atmosphere.

Although there are a lot of different greenhouse gases, carbon dioxide is the most important one that is produced by human activities. It is responsible for most of the “thickening of the blanket” that has trapped heat near the surface in recent decades.

Today in the United States, transportation -- emissions from cars, trucks, trains, boats and airplanes the largest source of carbon dioxide. Electricity generation is the second largest source. Together these two account for about two-third of energy-related emissions.  The rest come from industry, such as factories that make products we use, and from energy we use in our homes and businesses.

The Impacts

The Earth is warming. Thirteen of the 14 warmest years on record have all occurred since 2000. If we keep releasing greenhouse gases into the atmosphere, it will continue to warm. This warming brings an increased risk of climate impacts that include:

Heat waves. Heat waves are long periods of time with above-normal temperatures. As the Earth warms, more areas will be at risk for extreme heat waves. Learn more about the link between climate change and extreme heat.

Heavy Precipitation. Heavy downpours are becoming more common in many locations. Learn more about the link between heavy precipitation and climate change.

Sea Level Rise. Sea level has risen about 8 inches in the last century, making coastal storms more damaging. Scientists believe sea levels in the United States could rise 1 to 4 feet in the 21st century, and could be even higher if glaciers in Greenland or Antarctica melt especially quickly.

Threats to habitats and animals.  As temperatures warm, many plants and animals have been migrating to higher elevations or toward higher latitudes.  Some animals may have difficulty moving to or adapting to new habitats.

Ocean acidification. Extra carbon dioxide in the atmosphere is absorbed by the oceans, making them more acidic.  This can make it difficult for corals and microorganisms that form shells to survive.

Arctic melting. Arctic temperatures are increasing at about twice the rate of the rest of the world. Because of this, the amount of ice that covers the Arctic Ocean during the summer has been shrinking.

Wildfires. These are large fires that burn vast amounts of forests and brush. When they are not controlled, wildfires can destroy homes and be deadly. The number of large wildfires and the length of the wildfire season have been increasing in recent decades. Find out how climate change will worsen wildfire conditions.

Drought. Global warming will increase the risk of drought in some regions. Also, warmer temperatures can increase water demand and evaporation, stressing water supplies. Learn about the links between climate change and drought.


These impacts are already happening in many places around the world and will likely grow worse over time as warming continues.  

How can people slow warming and prepare for climate change?

There are two things we need to do:

The first is to reduce the greenhouse gas emissions responsible for climate change. We need to find ways to make energy that produce fewer greenhouse gas emissions. We also need to make those energy sources as inexpensive and easy to use as fossil fuels.

One way to reduce emissions is by using less energy, or using energy more efficiently. We can drive cars that use less gasoline or run on electricity or other alternative fuels. We can also use less energy in our homes, offices, and schools. Everyone can play a part in becoming more efficient, including government, businesses, and people like you. We'll talk about some things you can do to use less energy in the next section.

The second is to prepare for life in a changing climate. We need to make sure our buildings, roads, businesses and all the services they use can withstand the climate changes that we can’t avoid.

What can you do to help?

There are lot of things you can do to save energy and help stop global warming, like turning off the lights when you leave a room, taking shorter showers, and recycling. Now that you have some examples, you might be able think of your own ideas! Our Make an Impact program has a list of more things kids can do.

Want to learn more?

C2ES Basics

Koshland Science Museum: EarthLab

EPA Climate Change Website

EPA Kids Climate Change Website

National Climate Assessment

Basic global warming information facts for kids to learn how to stop the process.

The interdependence of water and energy

Have you ever thought that by leaving a light on, you’re wasting water, or that a leaky faucet wastes energy? It’s odd, but accurate.

That’s because water and energy are interrelated. Water is used in all phases of energy production, and energy is required to extract, pump, and move water for human consumption. Energy is also needed to treat wastewater so it can be safely returned to the environment.

C2ES recently hosted a series of webinars (video and slides here) on the intersection between water and energy (sometimes referred to as the “nexus”). The series was co-sponsored by the Association of Metropolitan Water Agencies and the Water Information Sharing and Analysis Center. Participants discussed how the water and energy sectors depend on each other and how they can work together to conserve resources.

Webinar - Water for Energy and Energy for Water: Innovation and Effective Stakeholder Engagement

Promoted in Energy Efficiency section: 
2 p.m. – 3 p.m. EDTView slides here.Watch video of the webinar.


Webinar 3: Innovation and effective stakeholder engagement on water and energy issues

July 24, 2014
2 p.m. – 3 p.m. EDT

Involving other stakeholders or partners for a water-energy project often leads to insights, innovations, and/or greater efficiency. In this third and final webinar, speakers from American Water and East Bay Municipal Utility District (EBMUD; California) discuss how they leveraged stakeholder involvement to address water-energy challenges and implement innovations. 

Suzanne Chiavari, Engineering Practice Leader from American Water, will describe some of her organization’s recent work in using renewable energy technologies, and how they’ve engaged community partners to establish greater integration across their resource management activities. Clifford Chan, Manager of Water Treatment and Distribution at EBMUD, will talk about two projects with multiple stakeholders that have helped the utility to implement its energy management strategy.

View slides here.
Watch video of the webinar.

Risky Business report shows need to act on climate change

You expect a business leader to keep a close eye on the bottom line and to act when a threat is clear. As C2ES and others have noted, it is increasingly clear to many business leaders that climate change is a here-and-now threat that we all -- businesses, government and individuals -- must address.

Today’s “Risky Business” report lays out in stark numerical terms the likely economic impact of climate change on U.S. businesses and the U.S. economy. The initiative – co-chaired by former New York City Mayor Michael Bloomberg, former Treasury Secretary Henry Paulson, and former hedge fund manager Tom Steyer – brings high-profile attention to this issue in the hopes that highlighting the risks and potential costs will help spur action to manage the impacts and curb climate-altering emissions.

The report’s outline of the many costs of climate impacts is likely an underestimate. For example, the impacts of diminishing groundwater are difficult to calculate and are not included.

IPCC AR5 Working Group III Highlights

On April 13, 2014, the Intergovernmental Panel on Climate Change (IPCC) released Working Group III’s report on the Mitigation of Climate Change.

The report notes that total greenhouse gas (GHG) emissions from 2000 to 2010 were the highest in human history, reaching 49 Gt CO2eq in 2010. Annual GHG emissions grew on average by 1 Gigatonne of carbon dioxide equivalent (Gt CO2eq) or 2.2 percent per year from 2000 to 2010, a higher rate than at any other period between 1970 to 2010.

Economic and population growth continue to be the most important drivers of emissions growth. Growth in GHG emissions since 1970, including the period of rapid emissions growth since 2000, have been driven by carbon dioxide emissions from fossil fuel combustion, land use changes, and industrial processes: carbon dioxide from these sources account for about 78 percent of the total GHG emission increase from 1970 to 2010.

Carbon dioxide is the major anthropogenic GHG, constituting 76 percent of total 2010 emissions. Methane accounts for 16 percent of emissions (on a CO2eq basis, assuming a 100-year time frame); nitrous oxide accounts for  6.2 percent; and fluorinated gases account for 2 percent.

The report lays out a number of “baseline” scenarios (those without additional mitigation actions or policies).  These scenarios lead to substantial warming by the end of the 21st century, with global mean surface temperature increases in 2100 from 3.7 to 4.8 degrees C (6.7 to 8.6 degrees F) relative to pre-industrial time.

In addition, a number of potential mitigation scenarios are also described.  These scenarios explore ways that some of this warming can be avoided, and how decisions in the near-term affect our ability to avoid longer-term warming.

  • To avoid 2 degrees C (3.6 degrees F) of warming relative to pre-industrial time, the report indicates that atmospheric concentrations of GHGs need to be stabilized around 450 ppm CO2-eq or lower. Given that we are currently around 430 CO2-eq, this is a tall order, requiring large-scale changes in energy systems and land use. For example, achieving this level of stabilization will require more rapid improvements in energy efficiency, and a tripling to nearly a quadrupling of the share of zero- and low-carbon energy supply from renewables, nuclear energy and fossil energy with carbon capture and storage, or bioenergy with carbon capture and storage, by the year 2050.
  • As one might expect, the aggregate economic cost of mitigation varies widely, but generally increases based on the stringency of the level of mitigation. In general, the costs of mitigation only offset a relatively small fraction of global projected economic growth for the 21st century.
  • The 2020 individual country-pledged goals (under the Cancún Agreements) are unlikely to put us on a path to avoid 2 degrees C (3.6 degrees F) of warming ; further substantial reductions beyond 2020 would need to be made. Continuing on the pathways consistent with the Cancún pledges is more consistent with scenarios likely to keep temperature change below 3 degrees C relative to pre-industrial levels.
  • If we do not strengthen mitigation efforts between now and 2030, it will be more difficult and more expensive to achieve warming targets, such as avoiding 2 degrees of warming relative to pre-industrial levels.


Figure SPM.1 from WG III report shows the global anthropogenic GHG emissions from 1970-2010, with the contribution from different gases shown by the colors.  To the right, the 2010 emissions are broken out, showing the relative uncertainties associated with each gas.  Note: “FOLU” is the acronym for “Forestry and Other Land Use.”


This portion of Figure SPM.4 from the WG III report shows the share of global energy that would need to come from low-carbon sources for four different mitigation scenarios.  For all the scenarios, the share of low-carbon energy is relatively large (>70% or higher) at the end of the 21st century.  Only the most aggressive scenarios (shown at the right side of the diagram, in dark and light blue) are likely to keep warming below 2 degrees Celsius – these scenarios include rapid growth of low-carbon energy, in which its share exceeds 50% of global energy by 2050.



Climate change poses national security risks at home and abroad

More than a dozen military leaders say the impacts of climate change threaten military readiness and response and will increase instability and conflict around the globe.

Their assessments are included in a recent report, National Security and the Accelerating Risks of Climate Change, by the CNA Corporation’s Military Advisory Board. The report’s authors – including 16 retired generals and admirals from the Army, Navy, Air Force, and Marine Corps – conclude that climate change impacts will act as threat multipliers and catalysts. Projected warming, changes in precipitation, sea level rise, and extreme weather events will pose risks to security within the U.S. and abroad.

At home, some of the threats are here and now. Many of the nation’s military installations are in coastal areas vulnerable to rising sea levels and storm surges. For example, the low-lying Hampton Roads area of Virginia is home to 29 military facilities. Sea level in the area is projected to rise 1.5 feet over the next 20-50 years and as much as 7.5 feet by the end of the century. One advisory board member, Brig. Gen. Gerald Galloway, stressed that “unless these threats are identified and addressed, they have the potential to disrupt day-to-day military operations, limit our ability to use our training areas and ranges, and put our installations at risk in the face of extreme weather events.”

Figure 1: Sea level rise projections for the Hampton Roads region, which is home to 29 different military facilities. Source: CNA, 2014

California's drought breaks records

In California, it’s almost impossible to avoid hearing about the drought. Restaurants serve water only upon request, “Save Our Water” radio ads run daily, and the issue headlines news broadcasts.

The persistent drought threatens to increase the risk of wildfires, damage crops, and harm wildlife. For example, UC Davis researchers estimate the state’s farm industry could lose $1.7 billion and nearly 15,000 jobs in 2014 due to the drought.

While Californians are no strangers to drought, this one in particular is cause for alarm. For the first time in the 15-year history of the National Drought Monitor, the entire state faces ‘severe’ (in yellow in Figure 1 below), ‘extreme’ (in red), or ‘exceptional’ (in dark red) levels of drought. In fact, October 2013-September 2014 could wind up being one of the driest periods in nearly 500 years.

Relief is unlikely to come soon. The Climate Prediction Center at the National Oceanic and Atmospheric Administration (NOAA) suggests the drought will persist and intensify in California through the summer.

Figure 1. The entire state of California is experiencing severe, extreme, or exceptional drought. This is the first time this has happened since the Drought Monitor began such classifications 15 years ago. Source: US Drought Monitor: California, (National Drought Mitigation Center, 2014),


National Climate Assessment

National Climate Assessment

People across the United States are dealing with the impacts of climate change: Farmers and ranchers across the Great Plains battle drought, transportation planners consider how floods might affect roads and bridges, and utility managers try to keep the electricity flowing during heat waves.

The Third National Climate Assessment (NCA), released May 6, 2014, is a compendium of the ways climate change affects our lives, livelihoods, and the economy in general. It describes how the climate has changed over the past century and provides a glimpse of future climate change and its impacts. The report also looks at how society is responding to a changing climate, and identifies actions we can take to prepare.

Read C2ES President Eileen Claussen's statement on the Third National Climate Assessment

What is the NCA?

The NCA is a congressionally mandated report to the president and Congress that “analyzes the effects of global change on the natural environment, agriculture, energy production and use, land and water resources, transportation, human health and welfare, human social systems, and biological diversity.”

It’s a comprehensive synthesis describing how the climate has changed in different regions of the country, and the impacts to these regions and various sectors that scientists expect in the 21st century.

The report advances the concept of climate change as a “risk management” challenge, laying out the critical services, like access to water and energy, and natural resources likely to be disrupted or harmed by climate impacts.

The NCA can be a useful tool for public and private sector decision-makers trying to address climate challenges.

What are the key findings?

The report tells us that:

  • Climate change is not just a problem for the future; it is happening here and now and is occurring faster than previously expected.
  • Changes in some U.S. weather extremes, like heat waves and heavy rainfall events, are related to human-induced climate change.
  • Climate impacts are threatening Americans’ health, infrastructure, water supplies, agriculture, ecosystems, and oceans.
  • The costs of climate change are high and will increase if emissions are not controlled.
  • Americans have tools at their disposal and are already beginning to take steps to reduce emissions, develop clean energy, and build resilient cities and industries that can withstand the effects of extreme weather.

The report identifies opportunities for adaptation, advocating that actions taken now are likely to return greater benefits than actions taken in the future. In addition, the NCA notes that efforts to reduce greenhouse gas emissions are critical for limiting the amount and rate of future climate change, giving adaptation investments a better chance of success.

How can I learn more?

The report is divided into several large sections. We provide links to these portions of the report and a short description of each.

Overview and Report Findings: Summarizes the assessment and the 12 top-line messages of the report.

Our Changing Climate: Explores observed and projected climate change at the global and national scale. Discussion focuses on physical changes, such as temperature, precipitation, and sea level. Observations tend to cover the last 50 to 100 years, while projections extend through the 21st century. Many maps and graphs in this section are referenced throughout the report.

Regions: Discusses in depth the observed and projected impacts for specific U.S. regions.


  • Northeast
  • Southeast and Caribbean
  • Midwest
  • Great Plains
  • Northwest
  • Southwest
  • Alaska
  • Hawaii and U.S. Pacific Islands
  • Oceans
  • Coasts

Sectors: Explores how climate affects economic, social, or ecological resources, typically cutting across geographic boundaries.

  • Water
  • Energy
  • Transportation
  • Agriculture
  • Forests
  • Ecosystems
  • Human Health

Cross-cutting sectors: Investigates how some types of communities are affected by climate impacts, the interrelationships among many resource decisions, and the large-scale changes in biogeochemistry that accompany climate change. Many of these chapters were not in previous assessments.

  • Urban infrastructure and vulnerability
  • Indigenous peoples, lands, and resources
  • Rural communities
  • Energy, water, and land use
  • Land use and land cover
  • Biogeochemical cycles

Responses: Looks at solutions, as well as the research, data, and tools that will facilitate the implementation of solutions.

  • Decision Support
  • Mitigation
  • Adaptation
  • Research Needs
  • Sustained Assessment

How is the report assembled?

The NCA was written by 240 authors with diverse expertise and experience. They include academic researchers; local, state, and federal government officials; private sector leaders; and non-profit experts. Their efforts are coordinated by the U.S. Global Change Research Program (USGCRP), a collaboration of 13 federal science agencies. A 60-member federal advisory committee, the National Climate Assessment Development Advisory Committee (NCADAC), oversees the development of the NCA report and makes recommendations about the ongoing assessment process.

Previous assessments were released in 2000 and 2009. The latest update is expected to be the start of an ongoing process in collecting and disseminating data and information through various digital media and user networks.

What is the difference between the NCA and IPCC reports?

The NCA is independent of reports issued by the Intergovernmental Panel on Climate Change (IPCC). Although both are based on the latest science, and reach similar conclusions, they differ significantly their scope and focus. Here are some key differences:

  • The NCA discusses observed and projected climate impacts in the United States, focusing on eight sub-regions, while the IPCC discusses observed and projected climate impacts at the continental scale.
  • The NCA is subject to review by the National Academy of Sciences, government agencies, and the public. The IPCC is subject to scientific and governmental review.
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