Climate Change: How do we know?

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.)

What is Climate Change?

Climate change is the term used to describe changes in average weather over time periods ranging from decades to millions of years. These changes may be driven by external forces (i.e. predictable orbital variations or solar variation), result from processes internal to the Earth (i.e. plate tectonics or volcanic activity) or be caused by human activities (anthropogenic) such as global warming.

A volcano erupts in Iceland, spewing Greenhouse Gases into the atmosphere.

The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.

To see how much the global temperature has risen since 1880, read here:

An increase in greenhouse gas levels (global warming) is one of the major impacts that humans have on climate.  These include carbon dioxide, water vapour, nitrous oxide, methane, ozone and halocarbons. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.

Ice core samples drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming.

Every year trees grow a new layer of bark. When you cut through a tree you can see these different layers as rings. The thicker the ring the better the growing conditions were that year. That allows scientists to work out what the temperature, precipitation and carbon dioxide levels are likely to have been for each year.

To understand the greenhouse effect better, go here:

The evidence for rapid climate change is compelling

The Republic of Maldives: Vulnerable to sea level rise
Sea level rise
  • Global sea level rose about 17 centimetres (6.7 inches) in the last century. The rate in the last decade, however, is nearly double that of the last century.

Texas State Park police officer Thomas Bigham walks across the cracked lake bed of O.C. Fisher Lake Wednesday, Aug. 3, 2011, in San Angelo, Texas. A bacteria called Chromatiaceae has turned the 1-to-2 acres of lake water remaining the colour red. A combination of the long periods of 100 plus degree days and the lack of rain in the drought -stricken region has dried up the lake that once spanned over 5400 acres. (AP Photo/Tony Gutierrez)
Global temperature rise
  •  All studies show that Earth has warmed since 1880. Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. The year 2015 was the first time the global average temperatures were 1 degree Celsius or more above the 1880-1899 average. Even though the 2000s witnessed a solar output decline, surface temperatures continue to increase.

Globally Warming Oceans Are Killing Coral Reefs, like here in Samoa.

Warming oceans
  •  The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of 0.302 degrees celsius since 1969.

This July 4, 2012, file photo provided by Ian Joughin shows surface melt water rushing along the surface of the Greenland Ice Sheet through a supra-glacial stream channel, south-west of Ilulissat, Greenland. Polar ice sheets are now melting three times faster than in the 1990s and the acceleration of the melting, especially in Greenland, has ice scientists worried. Michel Jarraud, secretary-general for the World Meteorological Organization, says the most troubling climate development in 2012 was the melting at the top of the world. (AP Photo/Ian Joughin)
Shrinking ice sheets
  • The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA  shows Greenland lost 150 to 250 cubic kilometres of ice per year between 2002 and 2006, while Antarctica lost about 152 cubic kilometres of ice between 2002 and 2005.


Warm temperatures and winds drove record declines in sea ice at both polar regions
Declining Arctic sea ice
  • Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.

Carroll Glacier, Alaska. August 1906 and June 21, 2004
Glacial retreat
  • Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.

Global warming is linked to extreme weather events.
Extreme events
  •  The number of record high-temperature events in the United States has been increasing, while the number of record low-temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events.

Coral reefs are a major concern in a world of increasing ocean acidification and nutrients.
Ocean acidification
  • Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tonnes per year.

These two natural-color satellite images of the reduction of snow cover in the Sierra Nevada
Decreased snow cover
  • Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.

Did you know?

Understanding global warming and climate change begins young:

How do volcanic eruptions affect the climate? Understand global dimming here:

What do volcanic eruptions mean for the climate?

Calbuco volcano eruption. Credit: Philip Oyarzo Calisto
See how Sunspots and Solar Cycles affect the climate:

Leave a reply!

1. Describe and explain two natural causes of climate change.
2. How has the earth’s climate changed since 1880 and why?
3. Describe how three of the pieces of evidence of climate change will affect you personally.

3 thoughts on “Climate Change: How do we know?”

  1. 1.two natural causes of climate change are volcanic eruptions and variations in solar output.volcanic eruptions is when a volcano erupts carbon dioxide , water vapour , sulfur dioxide,dusts and ash are released into the atmosphere. Dust and ash reflect the solar energy in space resulting in increase of temperature. Variations in solar output is the sunspots at cooler region of the sun that appear as dark spots as it is dark, it radiates heat thus compensates for the lower temperature of solar output.

    All studies show that Earth has warmed since 1880. Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. The year 2015 was the first time the global average temperatures were 1 degree Celsius or more above the 1880-1899 average. Even though the 2000s witnessed a solar output decline, surface temperatures continue to increase.Global temperature incerase due to gases trapping the earth and when heat from the sun energy reaches the atmosphere the gas traps heat that tries to escape thus making the earth temperature increase these gases are from factories burning of fossil fuels and agriculture. has affected me personally by teaching me the importance of helping to reduce global warming so as to save the earth .


    1. Hi Ryan, thanks for attempting this piece of homework. However, please do it on foolscap paper for your teacher to mark when school reopens. Also, please put more thought into question three: teaching you the importance of something is not an impact.

      Think instead of: how has higher temperature affected my life? How has higher rainfall affected my life? Have you experienced more extreme weather yourself or do you know anyone who has?

      Please go beyond cutting and pasting from the text. I have purposely put in questions that require personal thought. In this aspect, you need to put more deliberate thought into this: there are no textbook answers in real life.


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