CLIMATE CHANGE BASICS: From the Environmental Protection Agency
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.
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.