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April 20, 2014  |  Login
ecomii guides guide to global warming
In partnership with:  Union of Concerned Scientists

How much are humans contributing to global warming?

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While there are natural sources of the primary greenhouse gases, human activities have without a doubt overloaded and changed the atmosphere. Ever since the Industrial Revolution, we’ve been steadily producing and releasing carbon dioxide and other heat-trapping gases into the atmosphere. In 2005, global atmospheric concentrations of carbon dioxide were 35% higher than they were before the Industrial Revolution.1

Today, climate scientists, meteorologists and oceanographers are using high-tech tools and models to figure out just how much human activities have contributed to global warming. Using sophisticated computer programs and models, scientists can get a picture of how the Earth’s atmosphere and oceans respond to natural and human factors. Then they compare past climate patterns with these models to see which factors have contributed the most to global warming.

You can learn more about how scientists measure climate from the Natural Resources Defense Council.

Measuring the human fingerprint

The science proves that humans have left their mark all over global warming. The signs are showing up in the oceans, in the atmosphere and on land.

According to the Union of Concerned Scientists:

“The fingerprints that humans have left on Earth's climate are turning up in a diverse range of records and can be seen in the ocean, in the atmosphere, and at the surface.

"In its 2001 report, the Intergovernmental Panel on Climate Change stated, 'There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.' Carbon dioxide from fossil fuel burning and land clearing has been accumulating in the atmosphere, where it acts like a blanket keeping Earth warm and heating up the surface, ocean, and atmosphere. As a result, current levels of carbon dioxide in the atmosphere are higher than at any time during the last 650,000 years."

Fingerprint 1: The Ocean Layers Warm

The world’s oceans have absorbed about 20 times as much heat as the atmosphere over the past half-century, leading to higher temperatures not only in surface waters but also in water 1,500 feet below the surface. The measured increases in water temperature lie well outside the bounds of natural climate variation.

Fingerprint 2: The Atmosphere Shifts

Recent research shows that human activities have lifted the boundary of Earth's lower atmosphere. Known as the troposphere (from the Greek tropos, which means "turning"), this lowest layer of the atmosphere contains Earth's weather. The stable layer above is called the stratosphere. The boundary that separates the two layers, the tropopause, is as high as nine miles above the equator and as low as five miles above the poles. In an astounding development, a 2003 study showed that this tropopause has shifted upward over the last two decades by more than 900 feet. The rising tropopause marks another human fingerprint on Earth's climate.

Fingerprint 3: The Surface Heats Up

Measurements show that global average temperature has risen by 1.4 degrees Fahrenheit in the last 100 years, with most of that happening in the last three decades. By comparing Earth's temperature over that last century with models comparing climate drivers, a study showed that, from 1950 to the present, most of the warming was caused by heat-trapping emissions from human activities. In fact, heat-trapping emissions are driving the climate about three times more strongly now than they were in 1950.  ....read more

1. US EPA [26 July 2007]. [online] Available from: http://www.epa.gov/climatechange/emissions/co2.html. [27 November 2007]

2. Union of Concerned Scientists [28 June 2006]. [online] Excerpted from: http://www.ucsusa.org/global_warming/science/Fingerprints.html. [27 November 2007]

3. The Marshall Institute [undated]. Available from: http://www.marshall.org/subcategory.php?id=9. [13 December 2007]

 
 
 
 
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