Global Climate Change

Global average temperatures have warmed by 0.85° C since 1880. The years between 2000 and 2015 experienced nine out of the ten warmest years ever recorded. Greenland and Antarctic ice sheets, as well as glaciers around the world, have been shrinking at ever-faster rates. The increased temperatures and melting ice has caused average sea level to rise 19 cm since 1901. Do these changes represent a trend toward global warming, or is it simply part of a natural cyclic variation in climate? The answer from climate scientists around the world is unanimous that Earth's climate is warming, and that those rates are increasing.

Identify a Problem: Concentrations of Greenhouse Gases

If you have ever felt the Sun warm the inside of a car even while the air outside was cold, then you have experienced the greenhouse effect. Visible light from the sun travels through the clear walls of a greenhouse. The light is absorbed within and is transformed into thermal energy, which causes the air temperature to rise. Thermal energy is trapped, resulting in the warm interior. Earth's thick atmosphere acts as a greenhouse. The water vapor, carbon dioxide (CO2) methane, and nitrous oxides that are a natural part of Earth's atmosphere allow sunlight to pass through. The greenhouse gases, as they are called, trap thermal energy and prevent it from radiating back into space. Without the greenhouse effect, Earth's average temperature would be an unlivable -18°C.

The levels of atmospheric carbon dioxide and methane have increased rapidly during the last 150 years. This increase has been determined by analyzing air trapped in the ice layers of Greenland. Deeper sections of the ice contain air from earlier times. Since the beginning of human civilization, our atmosphere contained about 275 ppm (parts per million) of carbon dioxide, CO2. In the last 150 years, human activity has increased the concentrations of greenhouse gases. In 2015, the levels of CO2 were 402 ppm. Most of this increase is from burning fossil fuels such as coal, petroleum, and natural gas. Increases in greenhouse gas concentrations have already changed our climate. Thermal energy in the atmosphere drives weather patterns. It determines the rate of evaporation of water, and fuels the intensity of storms and other weather events. Global warming has already affected many natural systems through changes in patterns of rain and snowfall. Many regions have become more arid, and some now experience more intense rainfall. As a result, many plants and animals have been impacted, shifting the regions where they can inhabit, changing migration patterns. Humans depend on climate for our food supply. Changes in weather patterns have already had a negative impact on crop yields around the world. Increasingly intense weather has led to more frequent heat waves, droughts, floods, cyclones, and wildfires. The rise in sea level due to global warming has also increased the risks of floods along coastal areas.

Scientists around the world agree that without a change in greenhouse gas emissions, global climate will continue changing at ever-faster rates, causing the extinction of many species, and severe food and water shortages.

Brainstorm Solutions

What are some solutions for reducing greenhouse gases? One way is to decrease the output of greenhouse gases. This can be done by replacing electricity generated from burning coal with sources of renewable energy such as wind, solar, and hydroelectricity Another way to reduce greenhouse gas emissions is by using vehicles that are more efficient, and riding bicycles or walking when possible. Other alternatives include reducing energy used on heating and cooling, buying products that last longer, and by choices in the food that people eat. Another solution for reducing greenhouse gases is through land use. By planting trees and reducing deforestation, carbon dioxide can be captured and stored.

Agriculture, forestry and other forms of land use add about 25 percent of total greenhouse gases to the atmosphere. Scientists agree that changes in land-use can reduce emissions, and even capture CO2 from the atmosphere, making it a "sink" for CO2 over time.

Select a Solution

Greenhouse gases are as much a local as they are a global challenge. Solutions are likewise found at many levels. The daily habits and choices that people make have an effect across international borders. Lasting solutions can be based on international agreements to limit emissions on a global scale. There are many questions to consider. Which solutions are most effective? What are the costs associated with each technology? How easy is it to apply each? Many practical solutions also have several other benefits, such as being "cleaner," more cost-effective or healthier in the long run.

Communicate

The costs of global warming on natural and human systems are too great to ignore. Sometimes a change in habits and behaviors only happens when people understand the long-term effects of their choices. Lasting changes can happen when people understand that many of the changes that reduce greenhouse gas emissions have other lasting benefits. Additionally, some new technologies require an extra cost to adopt compared to the cost of keeping old technologies. Companies and people are sometimes encouraged to use emission-reducing technologies through financial incentives, education, and outreach programs.

For updated information on climate change indicators, see the UN News Story from May 2025, World Likely to breach 1.5 °C limit in next five years.