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The evidence of climate change is incredibly convincing and thorough. Scientists have worked for decades to gather it, employing advanced technology to ensure that we have a complete understanding of climate change works.

How Scientists Determine Evidence

Scientists have been measuring indicators of climate change since the late 1880s, starting with global air and sea temperatures. While originally measurements consisted of thermometers across the world, technology has progressed rapidly so that scientists can study the climate efficiently and accurately. Generally, scientists use satellites to measure key data points. Satellites are so important because they take measurements evenly across the world, even remote locations that are difficult or even impossible to get to. In addition, satellites virtually eliminate the risk of human error. After the data is collected by satellites, scientists now use advanced computer technology to map their data, allowing for faster climate knowledge. 

The Evidence of Climate Change

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Rising Global Temperatures

What We Know: Global temperatures have risen by a stunning 2.1ºF (1.2ºC) since 1880. While this number may not seem like a lot, small temperature changes can have significant impacts on the climate. Scientists estimate that the average temperatures during the Ice Age were only 9ºF (5ºC) cooler than today's average temperatures. Most importantly, this warming is the direct result of greenhouse gas emissions from industrial processes.

How We Know: Scientists have been taking exact readings of the surface and air temperatures since 1880. Since then, technology has progressed so that we now have precise ways to determine temperature with advanced instruments, including satellite technology. Scientists have also developed techniques to identify any error and produce an accurate result. Scientists have also studied the warming effect of greenhouse gases since the 1820s. Basic principles of physics and chemistry have told researchers that greenhouse gases warm the planet.

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Carbon Dioxide Levels

What We Know: Carbon dioxide levels have been increasing rapidly since the Industrial Revolution, when humans began burning fossil fuels. Carbon dioxide levels have reached a high over at least the last 800,000 years, which includes multiple ice age cycles. These levels are important because carbon dioxide is a greenhouse gas, meaning that it traps heat in the earth to keep it warm. While it is an important part of the earth's climate, too much carbon dioxide is leading to too-warm temperatures.

How We Know: When burning fossil fuels (which are carbon-based), the carbon mixes with oxygen in the air to form carbon dioxide. Indeed, through extensive climate modeling, scientists have concluded that carbon dioxide emissions in modern times overwhelmingly come from human sources. To determine carbon dioxide levels in ancient history, scientists use ice cores, which store information from particles trapped hundreds of thousands of years ago. These ice cores form the foundation of historical climate analysis.

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It's Not the Sun

What We Know: Solar radiation levels have not increased significantly over the last two hundred years. Scientists first measure the amount of solar radiation hitting the upper atmosphere, which directly indicates pure solar energy. In addition, since climate change only affects the lower atmosphere, where greenhouse gases are, there is only warming in the lower atmosphere. This is consistent with scientists' data.

How We Know: Scientists use satellites to measure incoming sunlight levels at the top of the atmosphere. These measurements ensure a complete understanding of how the sun's energy has changed. Scientists have used their research and knowledge of historical conditions to estimate solar levels since the 1600s.

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Sea Level

What We Know: Sea levels have risen by about eight inches since 1880. The rate of sea level rise is rapidly increasing: half of these eight inches occurred in the last thirty years, and sea level rise is 30% faster than in 1992. While the majority of sea level rise comes from glacial melt, warming oceans also play a role, as water expands when it warms, contributing to sea level rise. 

How We Know: Scientists use satellite radar technology to determine how sea levels have risen. This data determines the rate of sea level rise and its contributing factors (like glacial melt).

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Ice Loss and Glacial Retreat

What We Know: Glaciers have been melting at an increasingly alarming rate. Between 2000 and 2019, glaciers have lost 70.5 trillion gallons of water annually, not including ice sheets. Glaciers melt from a combination of warmer air and water temperatures, melting glaciers and ice sheets from above and below.

How We Know: Scientists use glacier inventories to track glacial change across the world. These inventories are managed by the world's top scientists and are carefully measured and double-checked to ensure accuracy. These inventories form the basis of our knowledge of glaciers and their melting.

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Warming Oceans

What We Know: 90% of the global temperature rise occurs in the ocean. As a result, overall ocean heat levels and surface temperatures have been increasing for decades. Since 1880, the average sea surface temperature has increased by 1.24ºC.

How We Know: Scientists use a combination of satellite technology and remote buoys and sensors to determine the heat content and sea surface temperatures. They then combine these measurements to verify their results are accurate, eliminating any bias in the data. These scientific methods combine to form a complete picture of ocean warming.

Why is the Evidence Important?

Understanding the evidence of climate change is important for two main reasons. First, it helps solidify your knowledge of climate change. The evidence forms the basis of our understanding of mitigating and adapting to climate change. Second, a full understanding of the evidence is essential for speaking to people about climate change. If someone disagrees about an aspect of climate change, it is essential to have all the facts and to understand how scientists got those facts. There is no point to learning about something if you do not also understand why it works.

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