The year 2013 tied with 1980 as the 34th warmest in 120 years of data for the 48 states in the contiguous U.S., according to the National Climatic Data Center (NCDC). This comes two years after the record warmth of 2012, which was substantially warmer – a full degree Fahrenheit – than any other year since records began in 1895.
Average temperature for the contiguous 48 U.S. states from 1895 through 2013. The red line is the 12-month average for each year. The green line is a calculation of the trend during each decade. The blue line shows the trend over the last century of records. The gray line is flat because it is a simple average for the entire period. (Image courtesy NOAA’s National Climatic Data Center.)
Don’t changes in natural systems such solar variations and volcanoes explain global warming? (UCAR/NCAR)
Warming by the Sun and other variations in natural systems cannot explain global warming. Experiments using computer models confirm the importance of human-produced emissions in the temperature trends of recent decades. The graph below shows global average temperature since 1890 as reproduced by the NCAR/DOE Parallel Climate Model. The simulations that include only natural variability (blue line), including changes in the Sun and eruptions of volcanoes, show that we should have seen a decrease in the global average temperature in the last several decades. The simulations that most closely resemble the observed record (red line) are the ones that take both human-induced changes and natural variations into account.
Global average temperature since 1890. The black line plots human observations of Earth’s temperature. The blue line summarizes simulations performed using only natural influences on climate (volcanoes and solar variations). The red line, from a set of simulations that includes sulfate aerosol pollution and greenhouse gases. Shading in pale blue and pale pink shows the range of results (model uncertainty) for each group of simulations. (Image courtesy Gerald Meehl, NCAR.)
Earth's Climate History
Hasn't the Earth's climate changed before? What's different about climate change today? (EPA Student)
Yes. The Earth's climate changed many times in the distant past as a result of natural causes, but today's climate change is different because people's activities are the main cause. This is also the first time modern society has had to deal with such large, widespread changes in climate. Rising sea level, stronger storms, droughts, and other effects of climate change will pose major challenges for people around the world.
How do we know what greenhouse gas and temperature levels were in the distant past? (NASA)
Ice cores are scientists’ best source for historical climate data. Every winter, some snow coating Arctic and Antarctic ice sheets is left behind and compressed into a layer of ice. By extracting cylinders of ice from sheets thousands of meters thick, scientists can analyze dust, ash, pollen and bubbles of atmospheric gas trapped inside. The deepest discovered ice cores are an estimated 800,000 years old. The particles trapped inside give scientists clues about volcanic eruptions, desert extent and forest fires. The presence of certain ions indicates past ocean activity, levels of sea ice and even the intensity of the sun. The bubbles can be released to reveal the make-up of the ancient atmosphere, including greenhouse gas levels.
Other tools for learning about Earth’s ancient atmosphere include growth rings in trees, which keep a rough record of each growing season’s temperature, moisture and cloudiness going back about 2,000 years. Corals also form growth rings that provide information about temperature and nutrients in the tropical ocean.
Why is it a problem if the Earth's average temperature gets a little warmer? (EPA Student)
Temperature plays an important role in how nature works, and even a small change in average temperature can have a noticeable impact on plants, animals, and other natural processes. For example, just a one- to two-degree increase in global temperature can lead to a much greater risk of wildfires. Some parts of the world are warming a lot more than average, which means the effects are much more dramatic.
In the past, has Earth been warmer than it is today? If so, does that mean we shouldn’t worry about global warming? (US Environmental Protection Agency [EPA])
There were times in the distant past when Earth was warmer than it is now. However, human societies have developed and thrived during the relatively stable climate that has existed since the last ice age. Due to excess carbon dioxide pollution, the climate is no longer stable and is instead projected to change faster than at any other time in human history. This rapid climate change will expose people to serious risks. Sea-level rise, increasing droughts and wildfires in some regions and increasing flooding in others, more heat waves, and other effects of climate change all pose risks to human health, infrastructure critical to homes, roads and cities, and the ecosystems that support us.
Greenhouse Gases and Carbon Dioxide
What is the greenhouse effect? (EPA Student and UCAR/NCAR)
The greenhouse effect is a natural process that helps make the Earth warm enough for us to live. Without the so-called greenhouse gases, including carbon dioxide, methane, nitrous oxide, and water vapor, Earth would be too cold to inhabit. These gases in Earth’s atmosphere absorb and emit heat energy, creating the greenhouse effect that keeps our planet’s temperature livable.
It works like this: The Earth gets energy from the sun, heats up, and then gives off energy in a different form, called infrared radiation. Greenhouse gases in the atmosphere trap some of this energy before it escapes to outer space, warming the atmosphere. But people's activities are adding extra greenhouse gases to the atmosphere, so the greenhouse effect is becoming stronger and the Earth is getting warmer.
Since the industrial revolution, people have burned vast amounts of coal, petroleum, and other fossil fuels to create heat and power. This releases carbon dioxide, the most plentiful human-produced greenhouse gas, into the atmosphere. The result: more heat is trapped in the Earth’s atmosphere instead of radiating out into space.
How much carbon dioxide (and other kinds of greenhouse gas) is already in the atmosphere? (UCAR/NCAR)
One of the strongest pieces of evidence for human-induced climate change is the consistent rise in carbon dioxide (CO2) in modern times, as measured at NOAA’s Mauna Loa Observatory in Hawaii, where CO2 has been observed since 1958. In early 2015, the seasonally adjusted concentration of CO2 in the Earth’s atmosphere was close to 400 parts per million (ppm). The last time the Earth’s atmosphere held this much carbon dioxide was at least 3 million years ago.
Monthly carbon dioxide concentrations at NOAA’s Mauna Loa Observatory. This graph shows an annual seasonal cycle and a steady upward trend since CO2 measurements began atop Mauna Loa, Hawaii, in 1958. (Image courtesy Scripps CO2 Program.)
Does the amount of carbon dioxide in the atmosphere go up every year? (UCAR/NCAR)
People don’t always produce more CO2 from one year to the next. When the global economy weakens, emissions from human activities can actually drop slightly for a year or two, as they did in 2009. When the economy rebounds, so can emissions. Yet in either case, the accumulation of CO2 in the atmosphere continues to rise over time.
Impacts of Climate Change
What are the impacts of climate change on weather?
Many of the most costly impacts of climate change – in terms of both life and property – will result from more frequent, longer-lasting, or more intense extreme weather events and associated natural disasters such as heavy precipitation events, floods, heat waves, droughts, and wildfires. A warmer atmosphere will hold more moisture, which means that when it does rain or snow, more water will be available to fall. Precipitation is therefore projected to be concentrated into more intense events.
How can a change of one or two degrees in global average temperatures have an impact on our lives? (EPA)
Changing the average global temperature by even a degree or two can lead to serious consequences around the globe. For about every 2 degrees Fahrenheit of warming, we can expect to see:
- 5-15% reductions in the yields of crops as currently grown.
- 3-10% increases in the amount of rain falling during the heaviest precipitation events, which can increase flood risks.
- 5-10% decreases in stream flow in some river basins, including the Arkansas and Rio Grande.
- 200-400% increases in the area burned by wildfire in parts of the western United States.
Could global warming be beneficial? (NCAR/UCAR)
There can be both positive and negative impacts. A modest increase in global temperatures could increase agricultural productivity in some areas by, for instance, lengthening the growing season. But in high latitude regions, where the warming is expected to be greatest, there is already strong evidence to suggest the current warming is having strong negative impacts, such as severe coastal erosion due to retreating sea ice, increasing sea level, and thawing of coastal permafrost. The thawing of tundra is having negative impacts on buildings, roads, and industry.
What are the most visible signs of climate change? (EPA Student)
You can't see the signs of climate change from one day to the next, but if you compare from year to year, the clues are everywhere! For example, as the Earth has become warmer, the average sea level around the world has risen by nearly 7 inches in the last 100 years, glaciers all over the world are shrinking, and many bird species are shifting northward. Some of the most obvious changes are happening in the Arctic, where the amount of ice in the ocean has decreased dramatically.
Can climate change harm plants and animals? (EPA Student)
Yes. Any change in the climate of an area can affect the plants and animals that live there. Some animals might adapt or move elsewhere, but others could have trouble surviving. For example, if the ice in the Arctic Ocean disappears, the animals that depend on this ice won't have anywhere else to go. Climate change also alters plants' and animals' life cycles. For example, some flowers are blooming earlier in the spring, while some animals are migrating at different times.
Is it too late to do anything about climate change? (EPA)
It is not too late to have a significant impact on future climate change and its effects on us. With appropriate actions by governments, communities, individuals, and businesses, we can reduce the amount of greenhouse gas pollution we release and lower the risk of much greater warming and severe consequences. Many of the actions that we can take to address climate change will have other benefits, such as cleaner, healthier air. In addition, communities can take action to prepare for the changes we know are coming.
What can we do to stop climate change? (EPA Student)
There are lots of things you, your friends, and your family can do each day to reduce greenhouse gas emissions. A major way that greenhouse gases get into the atmosphere is when people burn coal, oil, and natural gas for energy. Here are some simple steps you can take to use less energy:
- Turn off the lights when you leave a room.
- Turn off your computer and other electronic devices when you're not using them.
- Drive less. Instead, walk, ride your bike, or use public transportation if you can.
- Use less water.
- Create less waste.
- Recycle used paper, cans, bottles, and other materials
These frequently asked questions were selected from the following sources: