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Climate Change: How Do We Know?

For thousands of years, C02 was never above 300 parts per million. Since 1950, it has climbed to 400 parts per million

"Atmospheric CO2 Graph" is a derivative of "Untitled Image" by NASA under Public Domain / U.S. Government Works. This derivative is licensed CC BY 4.0 by FHI 360 for the Online Professional English Network (OPEN), sponsored by the U.S. Department of State.

Earth's climate has changed throughout history. In the last 650,000 years, there have been seven cycles of glacial advance and retreat. The last ice age ended about 12,000 years ago. This marked the beginning of the modern climate era — and of human civilization. Most of these climate changes are caused by very small variations in Earth’s orbit. These variations change the amount of solar energy our planet receives.

The current warming trend is significant. Most of it is extremely likely (greater than 95% probability) to be the result of human activity since the mid-20th century. The warming trend is progressing at an unprecedented rate.

Recent technological advances have allowed scientists to see the big picture. Scientists have been able to use new equipment, such as Earth-orbiting satellites.

With new technology, scientists have collected many different types of information about our planet. They have studied Earth's climate on a global scale. They have collected data from many different locations around the globe. They have collected data over many years. The data shows that the climate is changing.

We know that carbon dioxide and other gases are able to trap heat. In fact, we have known this since the mid-1800s. These gases affect the transfer of energy through the atmosphere. This fact is the basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases cause the Earth to warm.

Scientists have studied ice samples from Greenland, Antarctica, and tropical mountain glaciers. These ice samples show that Earth’s climate responds to changes in greenhouse gas levels.

Tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks also hold evidence. This evidence reveals that current warming is occurring at a very fast rate.

After the last Ice Age, there was a warming period. The earth recovered from a cold climate and grew warmer. Scientists have calculated the average rate of warming after an Ice Age. Global warming today is happening roughly ten times faster than the average rate of Ice-Age-recovery warming. Carbon dioxide from human activity is increasing more than 250 times faster than it did from natural sources after the last Ice Age.

The evidence for rapid climate change is clear:

Global Temperature Rise

Desert sun Photo by Ashim D’Silva on Unsplash under Unsplash license.

The planet's average surface temperature has risen about 2.05 degrees Fahrenheit (1.14 degrees Celsius) since the late 19th century. Increased carbon dioxide and other human-made emissions are driving this change. Most of the warming occurred in the past 40 years. The last six years have been the warmest years on record. 2016 was the warmest year and eight months out of that year were the warmest months on record.

Warming Oceans

Ocean sun setting Photo by Johannes Plenio on Unsplash under Unsplash license.

The ocean has absorbed much of the increased heat. The top 100 meters of the ocean have warmed more than 0.6 degrees Fahrenheit (0.33 degrees Celsius) since 1969. Earth stores 90% of its extra energy in the ocean.

Shrinking Ice Sheets

Melting ice in the mountains Photo by Max Kukurudziak on Unsplash under Unsplash license.

Ice sheets in Greenland and Antarctica have decreased in mass. Between 1993 and 2019, Greenland lost an average of 279 billion tons of ice per year. Antarctica lost about 148 billion tons of ice per year.

Glacial Retreat

Snow in the mountains Photo by Daniel Adler on Unsplash under Unsplash license.

Glaciers are retreating almost everywhere around the world. The glaciers are getting smaller and smaller. This has been observed in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa.

Decreased Snow Cover

Snow in the moun Photo by Aleks Dahlberg on Unsplash under Unsplash license.

Snow is melting earlier in the year in the Northern Hemisphere. We can see this in satellite images. Spring snow cover in the Northern Hemisphere has decreased over the past five decades.

Sea Level Rise

Flood in venice italy Photo by Egor Gordeev on Unsplash under Unsplash license.

Global sea levels rose about 8 inches (20 centimeters) in the last century. The oceans are becoming higher. In the last 20 years, the rate has been nearly double that of the last century. That rate is increasing slightly every year.

Declining Arctic Sea Ice

Ice floating in sea Photo by William Bossen on Unsplash under Unsplash license.

The amount and thickness of Arctic sea ice has declined rapidly over the last several decades. There is less Arctic sea ice than before and it is thinner.

Extreme Events

A strong storm Image by David Mark from Pixabay under Pixabay license.

The number of record high-temperature events in the United States has been increasing. The number of record low-temperature events has been decreasing, since 1950. The U.S. has also seen increasing numbers of intense rainfall events.

Ocean Acidification

Coral reef Photo by Francesco Ungaro on Unsplash under Unsplash license.

The ocean is becoming more acidic. The acidity of surface ocean waters has increased by about 30% since the beginning of the Industrial Revolution. This is the result of humans emitting more carbon dioxide into the atmosphere. More carbon dioxide has been absorbed into the ocean. The ocean has absorbed between 20% and 30% of total carbon dioxide emissions in recent decades.

© 2021 by FHI360. "Intermediate Reading Practice: Climate Change: How Do We Know?" for the Online Professional English Network (OPEN), sponsored by the U.S. Department of State with funding provided by the U.S. government and administered by FHI 360. This work is an adaptation of Climate Change How Do We Know? by NASA licensed under U.S. Government Works / Public Domain , and can be found here. . Adapted content is licensed under the Creative Commons Attribution 4.0 License, except where noted. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/