Signs of climate change

The Earth's climate is getting warmer, and the signs are everywhere. Rain patterns are changing, sea level is rising, and snow and ice are melting sooner in the spring. As global temperatures continue to rise, we'll see more changes in our climate and our environment. These changes will affect people, animals, and ecosystems in many ways.

Less rain can mean less water for some places, while too much rain can cause terrible flooding. More hot days can dry up crops and make people and animals sick. In some places, people will struggle to cope with a changing environment. In other places, people may be able to successfully prepare for these changes. The negative impacts of global climate change will be less severe overall if people reduce the amount of greenhouse gases we're putting into the atmosphere and worse if we continue producing these gases at current or faster rates.

The choices we make now and in the next few decades will determine how much the planet's temperature will rise. While we are not exactly sure how fast or how much the Earth's average temperature will rise, we know that:

• If people keep adding greenhouse gases into the atmosphere at the current rate, the average temperature around the world could increase by about 4 to 12°F by the year 2100.
• If we make big changes, like using more renewable resources instead of fossil fuels, the increase will be less—about 2 to 5°F.

•  

Higher temperatures mean that heat waves are likely to happen more often and last longer, too. Heat waves can be dangerous, causing illnesses such as heat cramps and heat stroke, or even death.

Warmer temperatures can also lead to a chain reaction of other changes around the world. That's because increasing air temperature also affects the oceans, weather patterns, snow and ice, and plants and animals. The warmer it gets, the more severe the impacts on people and the environment will be.

On average, the world is already getting more precipitation now than it did 100 years ago: 6 percent more in the United States and nearly 2 percent more worldwide.

The effects vary by region, though. For example, states in the Northeast are getting more precipitation than they used to get, but Hawaii is getting less.

What will happen in the future?

Precipitation is expected to increase in higher latitudes and decrease in areas closer to the Equator. The northern United States will become wetter while the South, particularly the Southwest, will become drier

Why does it matter?

Too little or too much water can be a problem. In many places, people depend on rain and snowmelt to fill lakes and streams and provide a source of water for drinking, watering crops, and other uses. However, heavy rain can cause flooding.

More droughts

A drought is an extended period of dry weather caused by a lack of rain or snow. As temperatures rise due to global climate change, more moisture evaporates from land and water, leaving less water behind. Some places are getting more rain or snow to make up for it, but other places are getting less.

What is happening now?

What will happen in the future?

Droughts are expected to keep getting longer and more severe. The U.S. Southwest is at particular risk for increasing droughts.

This map shows the results of computer models that have projected the risk of drought for the years 2090 to 2099. Source: Adapted from Dai (2011).

Why does it matter?

A drought means there's less water available for drinking, watering crops, making electricity at hydroelectric dams, and other uses. For example, an ongoing drought in the U.S. Southwest is straining water supplies in states like Nevada and Arizona, where water is already scarce.

Why does sea level change by different amounts in differnt places

Sea level is rising faster in some places than others because of wind patterns, ocean currents, and other factors. In addition, sea level may seem like it's 

changing more in certain places than others because the land itself may be rising or sinking.

In some places, the land is rising or sinking because of plate tectonics—the same forces that cause earthquakes, create volcanoes, and build mountain 

ranges. In addition to plate tectonics, land can also sink because people have pumped lots of oil, natural gas, or water out of the ground. When the land 

is also rising, sea level rise might not seem so bad. But in coastal areas where the land is sinking, the effects of sea level rise will be even worse

What will happen in the future?

The world's oceans are absorbing more carbon dioxide, as shown by the three sets of measurements in this graph. More carbon dioxide means more acidity (lower pH). Source: EPA's Climate Change Indicators (2010).

Acidity is measured using the pH scale. The lower the pH, the more acidic the substance. For more information about pH, visit:www.epa.gov/acidrain/measure/ph.html. Source: Adapted fromEnvironment Canada (2010).

Increasing acidity will make it harder for corals to build skeletons and for shellfish to build the shells they need for protection. Corals are particularly important because they provide homes for many other sea creatures.

Shrinking sea ice
 

The Arctic Ocean around the North Pole is so cold that it is usually covered with ice. In the winter, the area covered by ice gets bigger, and in the summer it gets smaller. If the air and water are warmer than usual, Arctic sea ice will melt more than usual during the summer.

What is happening now?

The amount of summer ice in the Arctic Ocean in recent years was the smallest it's been since scientists started using satellites to measure the area covered by ice back in the 1970s. The ice is also getting thinner.

What will happen in the future?

Overall, Arctic sea ice will continue to shrink in the coming decades. However, the amount of sea ice may vary from year to year depending on factors such as local temperatures, wind patterns, and ocean currents.

Why does it matter?

Many animals depend on sea ice for their homes and hunting grounds, and native people in the Arctic need these animals as a source of food. In addition, ice and snow reflect a lot of sunlight back out to space and help keep the planet from getting too warm. If there's less ice, the Earth will absorb more energy from the sun and get even warmer. This is an example of a positive feedback loop, which happens when warming causes changes that lead to even more warming.

Melting Glaciers

Glaciers are large sheets of snow and ice that are found on land all year long. They're found in the western United States, Alaska, the mountains of Europe and Asia, and many other parts of the world. Warmer temperatures cause glaciers to melt faster than they can accumulate new snow.

What is happening now?

Glaciers all over the world have been melting for at least the last 50 years, and the rate of melting is speeding up. Many glaciers in Alaska and other parts of the United States have shrunk dramatically.

What will happen in the future?

If temperatures keep rising, glaciers will continue melting, and some could disappear completely.

Source: Post (1958) and Nolan (2003), National Snow and Ice Data Center

Why does it matter?

Less snowpack

Snowpack refers to the total amount of snow and ice on the ground. In high mountain ranges and other cold places, snowpack builds up in the winter and melts in the spring and summer. As the world gets warmer, some places will get more rain instead of snow, so the snowpack won't be as deep. Plus, when the air is warmer, snow melts faster.

What is happening now?

Many places have less snowpack than they used to, and this snowpack is melting earlier. For example, the map on the right shows that in many parts of North America, Europe, and Asia, snow doesn't stay on the ground in the spring as long as it used to.

What will happen in the future?

When snowpack melts in spring and summer, it provides fresh water for rivers and streams, and it fills reservoirs that supply drinking water to cities and towns. Snowpack is also important for winter sports like skiing and snowboarding.

Thawing permafrost 

Permafrost refers to a layer of soil or rock that is frozen all year round. Permafrost is found throughout much of Alaska, parts of Canada, and other countries in the far north. You might think a place with permafrost would be barren, but plants can still grow in the soil at the surface, which is not frozen during warmer parts of the year. However, there may be a thick layer of permafrost underneath. As air temperature rises, so does the temperature of the ground, which can cause permafrost to thaw (or melt).

What is happening now?

As temperatures keep getting warmer, permafrost will continue to thaw. For example, the map on the right shows how permafrost in northwestern Alaska could change by the year 2100.

Next month we will look into the effects climate change has on people and the environment.